ML14260A043
Text
Page 1 of 8 GEO.DCPP.TR.14.04 R0 Appendix A APPENDIX A Sensitivity Study for Optimum OBS Station Locations
Page 2 of 8 GEO.DCPP.TR.14.04 R0 Appendix A Dr. Felix Waldhauser performed various sensitivity tests using synthetic earthquake locations to find the optimal OBS locations that also fit the permitting requirements. Waldhausers analysis method and selected results are shown at the end of his email train.
He felt that synthetic tests Syn04.2 and Syn05.2 were considered good array designs that would meet our objectives. The Syn04 design would probably record and locate very small events on the shoreline fault right off-shore DC (Figure 1). The Syn05 design would be optimized to best constrain events towards the fault intersection, and produce better network criteria for events on the Hosgri fault (Figure 2). However, due to the constraints set by the permitting agencies, designs Syn04.2 and Syn05.2 had to be modified. The results labeled syn07.2_20km and syn07.2_55km are the preferred OBS locations (Figure 3). Figure 4 shows the final locations and corresponding errors from HYPOINVERSE for synthetic events recorded at stations within 20 km (top) and 55 km (bottom). These final results were used to write the request for proposal.
Details of these tests are described in the emails below.
From:
felixw@ldeo.columbia.edu
Subject:
Re: synthetics setup Date: September 15, 2010 5:56:42 PM EDT To:
MKM2@pge.com Cc:
felixw@ldeo.columbia.edu Write-up:
Synthetic travel times (P and S) were computed using a grid of synthetic sources (open circles) and the McLaren and Savage model (M&S,2001) in order to get the network parameters for each source. Criteria are essentially thresholds of the parameters I determine, e.g. the number of stations within 10 km is a parameters, and the criteria as shown in the figures are 3 recording stations or more within 10 km..
Red sources indicate all sources that have the following network criteria:
- 1) At least one station within 5 km (to constrain shallow events)
- 2) At least 3 stations within 10 km (to best constrain events down to seismogenic depth)
- 3) Max azimuthal gap < 180 deg (to constrain epicenter)
(See Email date September 22, 2010 for the definition of yellow sources.)
Network parameters are based on the four OBS and the permanent land stations.
Maps are created for two sets of OBS configurations (syn01 and syn02), and for max station distances of 20 km and 55 km to simulate small and larger earthquakes.
These maps indicate the area that is reliably covered by the given OBS configuration.
Also shown are the respective hypoinverse solutions and associated standard errors, derived after adding noise with a standard deviation of 0.05 s for P-and 0.1 s for S-
Page 3 of 8 GEO.DCPP.TR.14.04 R0 Appendix A waves to the perfect travel times at all stations.
I posted new figures w/ slightly different filenames:
station set up syn01 (the old one) showing network criteria and location error (z color coded) information:
http://www.ldeo.columbia.edu/~felixw/PGE/2010/syn01_20km_netwcrit.eps http://www.ldeo.columbia.edu/~felixw/PGE/2010/syn01_20km_locerr.eps http://www.ldeo.columbia.edu/~felixw/PGE/2010/syn01_55km_netwcrit.eps http://www.ldeo.columbia.edu/~felixw/PGE/2010/syn01_55km_locerr.eps station set up syn02 (per our phone conversation) showing network criteria and location error (z color coded) information:
http://www.ldeo.columbia.edu/~felixw/PGE/2010/syn02_20km_netwcrit.eps http://www.ldeo.columbia.edu/~felixw/PGE/2010/syn02_20km_locerr.eps http://www.ldeo.columbia.edu/~felixw/PGE/2010/syn02_55km_netwcrit.eps http://www.ldeo.columbia.edu/~felixw/PGE/2010/syn02_55km_locerr.eps From:
felixw@ldeo.columbia.edu
Subject:
Re: Best spots?
Date: September 22, 2010 6:09:05 PM EDT To:
MKM2@pge.com Cc:
felixw@ldeo.columbia.edu I posted two new sets of OBS locations, syn04 and syn05, that I find give the best monitoring capabilities:
http://www.ldeo.columbia.edu/~felixw/PGE/2010/syn04.1_55km_netwcrit.eps http://www.ldeo.columbia.edu/~felixw/PGE/2010/syn04.2_55km_netwcrit.eps http://www.ldeo.columbia.edu/~felixw/PGE/2010/syn04.1_20km_netwcrit.eps http://www.ldeo.columbia.edu/~felixw/PGE/2010/syn04.2_20km_netwcrit.eps http://www.ldeo.columbia.edu/~felixw/PGE/2010/syn05.1_55km_netwcrit.eps http://www.ldeo.columbia.edu/~felixw/PGE/2010/syn05.2_55km_netwcrit.eps http://www.ldeo.columbia.edu/~felixw/PGE/2010/syn05.1_20km_netwcrit.eps http://www.ldeo.columbia.edu/~felixw/PGE/2010/syn05.2_20km_netwcrit.eps I computed the network criteria for both the original line sources along the Shoreline and Hosgri faults, and the 'carpet' sources that I used in the most recent figures. I also added, in yellow, a more stringent network criteria:
red (original):
at least 3 stations within 10 km at least one station within 5 km max azimuthal station gap < 180 yellow (new):
Page 4 of 8 GEO.DCPP.TR.14.04 R0 Appendix A at least 3 stations within 10 km at least one station within 3 km max azimuthal station gap < 110 Both station configurations monitor the area you indicated well (red dots). In the case of syn04 I optimized them to get the best network criteria for sources off-shore Diablo Canyon (yellow dots). With syn04 you are probably able to record and locate very small events on the shoreline fault right off-shore DC. Syn05 is optimized to best constrain events a bit more to the north towards the fault intersection, and produces better network criterias for events on the Hosgri fault.
Note that I increased the source density so the covered area is a bit easier to see. I avoided placing the OBSs on faults. Note that syn05 requires longer cables.
From:
felixw@ldeo.columbia.edu
Subject:
Re: Best spots? + need final SFZ analysisreport Date: September 24, 2010 12:11:35 PM EDT To:
MKM2@pge.com Cc:
felixw@ldeo.columbia.edu I uploaded syn06 and syn07.
http://www.ldeo.columbia.edu/~felixw/PGE/2010/syn06.1_20km_netwcrit.eps http://www.ldeo.columbia.edu/~felixw/PGE/2010/syn06.2_20km_netwcrit.eps http://www.ldeo.columbia.edu/~felixw/PGE/2010/syn06.1_55km_netwcrit.eps http://www.ldeo.columbia.edu/~felixw/PGE/2010/syn06.2_55km_netwcrit.eps http://www.ldeo.columbia.edu/~felixw/PGE/2010/syn07.1_20km_netwcrit.eps http://www.ldeo.columbia.edu/~felixw/PGE/2010/syn07.2_20km_netwcrit.eps http://www.ldeo.columbia.edu/~felixw/PGE/2010/syn07.1_55km_netwcrit.eps http://www.ldeo.columbia.edu/~felixw/PGE/2010/syn07.2_55km_netwcrit.eps syn06: moved O2 NE as you suggested, and O3 a bit south to improve coverage.
syn07: move O2 N. Builds a tight array near the fault intersection.
In both configuration control of events along the Hosgri fault in the SW corner is lost for small events.
Page 5 of 8 GEO.DCPP.TR.14.04 R0 Appendix A Figure 1. Synthetic test 04.2 showing network criteria needed for this design (red and yellow criteria described in emails above) for maximum stations distances of 20 km (top) and 55 km (bottom). Onshore OBS and onshore stations are represented by blue squares.
Page 6 of 8 GEO.DCPP.TR.14.04 R0 Appendix A Figure 2. Synthetic test 05.2 showing network criteria needed for this design (red and yellow criteria described in emails above) for maximum stations distances of 20 km (top) and 55 km (bottom). Onshore OBS and onshore stations are represented by blue squares.
Page 7 of 8 GEO.DCPP.TR.14.04 R0 Appendix A Figure 3. Preferred results. Synthetic test 07.2 showing network criteria needed for this design (red and yellow criteria described in emails above) for maximum stations distances of 20 km (top) and 55 km (bottom). Onshore OBS and onshore stations are represented by blue squares.
Page 8 of 8 GEO.DCPP.TR.14.04 R0 Appendix A Figure 4. Locations and corresponding errors from HYPOINVERSE for synthetic events recorded at stations within 20 km (top) and 55 km (bottom). Size of '+' represents lateral errors; vertical errors are color coded. Onshore OBS and onshore stations are represented by blue squares.
APPENDIX B Calibrations, Hydrostatic Test Report, and Technical Manual Page 1 of 81 GEO.DCPP.TR.14.04 R0 Appendix B
Page 2 of 81 GEO.DCPP.TR.14.04 R0 Appendix B
Page 3 of 81 GEO.DCPP.TR.14.04 R0 Appendix B
Page 4 of 81 GEO.DCPP.TR.14.04 R0 Appendix B
Page 5 of 81 GEO.DCPP.TR.14.04 R0 Appendix B
Page 6 of 81 GEO.DCPP.TR.14.04 R0 Appendix B
Page 7 of 81 GEO.DCPP.TR.14.04 R0 Appendix B
Page 8 of 81 GEO.DCPP.TR.14.04 R0 Appendix B
Page 9 of 81 GEO.DCPP.TR.14.04 R0 Appendix B
Page 10 of 81 GEO.DCPP.TR.14.04 R0 Appendix B
Page 11 of 81 GEO.DCPP.TR.14.04 R0 Appendix B
Page 12 of 81 GEO.DCPP.TR.14.04 R0 Appendix B
Page 13 of 81 GEO.DCPP.TR.14.04 R0 Appendix B
Page 14 of 81 GEO.DCPP.TR.14.04 R0 Appendix B
Page 15 of 81 GEO.DCPP.TR.14.04 R0 Appendix B
Page 16 of 81 GEO.DCPP.TR.14.04 R0 Appendix B
Page 17 of 81 GEO.DCPP.TR.14.04 R0 Appendix B
Page 18 of 81 GEO.DCPP.TR.14.04 R0 Appendix B
Page 19 of 81 GEO.DCPP.TR.14.04 R0 Appendix B
Page 20 of 81 GEO.DCPP.TR.14.04 R0 Appendix B
Page 21 of 81 GEO.DCPP.TR.14.04 R0 Appendix B
Page 22 of 81 GEO.DCPP.TR.14.04 R0 Appendix B
Page 23 of 81 GEO.DCPP.TR.14.04 R0 Appendix B
Page 24 of 81 GEO.DCPP.TR.14.04 R0 Appendix B
Page 25 of 81 GEO.DCPP.TR.14.04 R0 Appendix B
Page 26 of 81 GEO.DCPP.TR.14.04 R0 Appendix B
Page 27 of 81 GEO.DCPP.TR.14.04 R0 Appendix B
Page 28 of 81 GEO.DCPP.TR.14.04 R0 Appendix B
Page 29 of 81 GEO.DCPP.TR.14.04 R0 Appendix B
Page 30 of 81 GEO.DCPP.TR.14.04 R0 Appendix B
Page 31 of 81 GEO.DCPP.TR.14.04 R0 Appendix B
Page 32 of 81 GEO.DCPP.TR.14.04 R0 Appendix B
Page 33 of 81 GEO.DCPP.TR.14.04 R0 Appendix B
Page 34 of 81 GEO.DCPP.TR.14.04 R0 Appendix B
Page 35 of 81 GEO.DCPP.TR.14.04 R0 Appendix B
Page 36 of 81 GEO.DCPP.TR.14.04 R0 Appendix B
Page 37 of 81 GEO.DCPP.TR.14.04 R0 Appendix B
Page 38 of 81 GEO.DCPP.TR.14.04 R0 Appendix B
Page 39 of 81 GEO.DCPP.TR.14.04 R0 Appendix B
Page 40 of 81 GEO.DCPP.TR.14.04 R0 Appendix B
Page 41 of 81 GEO.DCPP.TR.14.04 R0 Appendix B
Page 42 of 81 GEO.DCPP.TR.14.04 R0 Appendix B
Page 43 of 81 GEO.DCPP.TR.14.04 R0 Appendix B
Page 44 of 81 GEO.DCPP.TR.14.04 R0 Appendix B
Page 45 of 81 GEO.DCPP.TR.14.04 R0 Appendix B
Page 46 of 81 GEO.DCPP.TR.14.04 R0 Appendix B
Page 47 of 81 GEO.DCPP.TR.14.04 R0 Appendix B
Page 48 of 81 GEO.DCPP.TR.14.04 R0 Appendix B
Page 49 of 81 GEO.DCPP.TR.14.04 R0 Appendix B
Page 50 of 81 GEO.DCPP.TR.14.04 R0 Appendix B
Page 51 of 81 GEO.DCPP.TR.14.04 R0 Appendix B
Page 52 of 81 GEO.DCPP.TR.14.04 R0 Appendix B
Page 53 of 81 GEO.DCPP.TR.14.04 R0 Appendix B
Page 54 of 81 GEO.DCPP.TR.14.04 R0 Appendix B
Page 55 of 81 GEO.DCPP.TR.14.04 R0 Appendix B
Page 56 of 81 GEO.DCPP.TR.14.04 R0 Appendix B
Page 57 of 81 GEO.DCPP.TR.14.04 R0 Appendix B
Page 58 of 81 GEO.DCPP.TR.14.04 R0 Appendix B
Page 59 of 81 GEO.DCPP.TR.14.04 R0 Appendix B
Page 60 of 81 GEO.DCPP.TR.14.04 R0 Appendix B
Page 61 of 81 GEO.DCPP.TR.14.04 R0 Appendix B
Page 62 of 81 GEO.DCPP.TR.14.04 R0 Appendix B
Page 63 of 81 GEO.DCPP.TR.14.04 R0 Appendix B
Page 64 of 81 GEO.DCPP.TR.14.04 R0 Appendix B
Page 65 of 81 GEO.DCPP.TR.14.04 R0 Appendix B
Page 66 of 81 GEO.DCPP.TR.14.04 R0 Appendix B
Page 67 of 81 GEO.DCPP.TR.14.04 R0 Appendix B
Page 68 of 81 GEO.DCPP.TR.14.04 R0 Appendix B
Page 69 of 81 GEO.DCPP.TR.14.04 R0 Appendix B
Page 70 of 81 GEO.DCPP.TR.14.04 R0 Appendix B
Page 71 of 81 GEO.DCPP.TR.14.04 R0 Appendix B
Page 72 of 81 GEO.DCPP.TR.14.04 R0 Appendix B
Page 73 of 81 GEO.DCPP.TR.14.04 R0 Appendix B
Page 74 of 81 GEO.DCPP.TR.14.04 R0 Appendix B
Page 75 of 81 GEO.DCPP.TR.14.04 R0 Appendix B
Page 76 of 81 GEO.DCPP.TR.14.04 R0 Appendix B
Page 77 of 81 GEO.DCPP.TR.14.04 R0 Appendix B
Page 78 of 81 GEO.DCPP.TR.14.04 R0 Appendix B
Page 79 of 81 GEO.DCPP.TR.14.04 R0 Appendix B
Page 80 of 81 GEO.DCPP.TR.14.04 R0 Appendix B
Page 81 of 81 GEO.DCPP.TR.14.04 R0 Appendix B
APPENDIX C Acceptance Test Plans and Sign-offs Page 1 of 16 GEO.DCPP.TR.14.04R0 Appendix C
Page 2 of 16 GEO.DCPP.TR.14.04R0 Appendix C
Page 3 of 16 GEO.DCPP.TR.14.04R0 Appendix C
Page 4 of 16 GEO.DCPP.TR.14.04R0 Appendix C
Page 5 of 16 GEO.DCPP.TR.14.04R0 Appendix C
Page 6 of 16 GEO.DCPP.TR.14.04R0 Appendix C
Page 7 of 16 GEO.DCPP.TR.14.04R0 Appendix C
Page 8 of 16 GEO.DCPP.TR.14.04R0 Appendix C
Page 9 of 16 GEO.DCPP.TR.14.04R0 Appendix C
Page 10 of 16 GEO.DCPP.TR.14.04R0 Appendix C
Page 11 of 16 GEO.DCPP.TR.14.04R0 Appendix C
Page 12 of 16 GEO.DCPP.TR.14.04R0 Appendix C
Page 13 of 16 GEO.DCPP.TR.14.04R0 Appendix C
Page 14 of 16 GEO.DCPP.TR.14.04R0 Appendix C
Page 15 of 16 GEO.DCPP.TR.14.04R0 Appendix C
Page 16 of 16 GEO.DCPP.TR.14.04R0 Appendix C
APPENDIX D Site Acceptance Test Results Page 1 of 10 GEO.DCPP.TR.14.04 R0 Appendix D
PG&E Site acceptance test. (SAT) 11/24/13 Present: Jim Cullen, Chris Pearcey FAT complete OK PDT complete OK Guralp performance test.
Time series evaluation.
Time series period 1 hour1.157407e-5 days <br />2.777778e-4 hours <br />1.653439e-6 weeks <br />3.805e-7 months <br /> for velocity sensors.
Page 2 of 10 GEO.DCPP.TR.14.04 R0 Appendix D
Time series period of 10 seconds for velocity sensors.
1 second section of data from velocity sensors.
Page 3 of 10 GEO.DCPP.TR.14.04 R0 Appendix D
PSD for vertical velocity channels.
PSD for North South velocity channels.
Page 4 of 10 GEO.DCPP.TR.14.04 R0 Appendix D
PSD for East West velocity channels 60 Hz signal observed. Physical coupling of AC/DC PSU to sensor system is the likely cause. The observed 60Hz signal is a result of the relocation of the junction box on to the sensor dome, which was a request made to allow permitting requirements to be met. This should not effect the primary objectives of this network.
Time series period 1 hour1.157407e-5 days <br />2.777778e-4 hours <br />1.653439e-6 weeks <br />3.805e-7 months <br /> for acceleration sensors.
Page 5 of 10 GEO.DCPP.TR.14.04 R0 Appendix D
Time series period 10 seconds for acceleration sensors.
Time series period 1 second for acceleration sensors.
Page 6 of 10 GEO.DCPP.TR.14.04 R0 Appendix D
PSD of Vertical acceleration channels PSD of North South acceleration channels Page 7 of 10 GEO.DCPP.TR.14.04 R0 Appendix D
PSD of East West acceleration channels.
Page 8 of 10 GEO.DCPP.TR.14.04 R0 Appendix D
Status data of each sensor system.
OBS-1 OBS-2 OBS-3 Page 9 of 10 GEO.DCPP.TR.14.04 R0 Appendix D
OBS-4 Page 10 of 10 GEO.DCPP.TR.14.04 R0 Appendix D
APPENDIX E As-Laid ROV Survey Page 1 of 15 GEO.DCPP.TR.14.04 R0 Appendix E
369 Pacific Street San Luis Obispo, California 93401 805-786-2650 Fax 805-786-2651 January 31, 2014 Project No. 1102-0621 PG&E Geosciences Department 245 Market Street San Francisco, California 94105 Attention: Ms. Marcia McLaren Senior Seismologist
Subject:
PG&E Point Buchon Ocean Bottom Seismometer Project, As-Laid ROV Survey Report
Dear Ms. McLaren:
In accordance with the California State Lands Commission (CSLC) issued lease, Padre Associates, Inc. (Padre) is pleased to submit this report for the subject Project for your submittal to CSLC. This report summarizes the results of the as-laid survey of the ocean bottom seismometer (OBS) system. Included in this report is Attachment A which contains figures of the OBS locations and cable route, and photographs from the ROV survey.
INTRODUCTION As part of Pacific Gas & Electric Companys (PG&E) seismic safety assessment at the Diablo Canyon Power Plant (DCPP), an OBS system was installed in the nearshore waters off Pt. Buchon, San Luis Obispo County (Attachment A - Figures 1, 2 and 3). The system is comprised of four long-term OBS units, approximately 11.5 miles (mi) (18.5 kilometer [km]) of 2-inch (in) (5-centimeter [cm]) diameter cable that provides power to the OBSs and transmitted data to and from the shorebased facility within DCPP, and two temporary OBS units. The temporary OBS units were installed for seventeen weeks and removed in November 2013. The cable for the long-term OBS units enters the DCPP facility through a PVC conduit, which extends into the marine waters of the DCPP intake embayment adjacent to the power plant.
Initial installation of those units and cable was completed from July 20 through July 27, 2013.
Final adjustments to the system were made between November 6 and November 24, 2013.
PG&E accepted the fully-adjusted system on November 24, 2013.
Regulatory requirements specified that following installation (including completion of all adjustments) of the OBS system, a post-installation (as-laid) visual survey of the entire cable route and OBS locations was to be completed by a qualified contractor. Tenera Environmental (Tenera) was retained by PG&E to complete a diver survey of the nearshore segment from the PVC conduit to the 80 foot (ft) (24 meter [m]) isobath. Padre was retained to complete the deeper water segments of the cable corridor, seaward of the 80 ft [24 m] isobath.
Lease conditions also specified that the results of the as-laid survey were to be presented in a technical report and on a series of maps (Figures 1, 2 and 3). The final alignment of the cable, final locations of the long-term OBS units, and an assessment of impacts to the seafloor habitat and associated biota were to be provided to various regulatory and resource agencies within the periods specified in the lease. The following discusses the results of Teneras and Padres surveys and provides the aforementioned assessment of impacts.
Page 2 of 15 GEO.DCPP.TR.14.04 R0 Appendix E
PG&E Geosciences Department January 31, 2014 (1102-0621)
C:\\USERS\\JKLAIB.PADRE-JENNKLAIB\\DOCUMENTS\\PG&E OBS\\FINAL PGE ROV SURVEY LTR 11-0621 013114.DOC METHODS AND EQUIPMENT The nearshore segment (between the offshore end of the conduit within the DCPP intake embayment and the 80 ft [24 m]) isobath was surveyed by Tenera divers using SCUBA.
The dive survey was completed on October 16, 2013. Divers collected latitude/longitude coordinates of the as-laid nearshore cable alignment, and completed underwater videography to document habitats and species along the cable. The submerged cable was videotaped using a Sony Handycam Model HDR-CX550V digital video camera inside a Light and Motion Bluefin 550 waterproof housing. At the same time, divers towed a Garmin ETrex Legend GPS unit.
The unit was attached to a surface float with the tether line held taught to keep the GPS unit directly above the divers. This provided a trackline of latitude/longitude coordinates for the nearshore cable segment. A technical report, a GIS shapefile with the coordinates of the cable alignment, and a video were provided to PG&E as separate deliverables.
The ROV survey was completed over a three-day period (December 6, 8, and 9, 2013).
Offshore segments and locations of the two temporary OBS units were surveyed with a Phantom 2+2 ROV, owned and operated by Aqueos Corporation under subcontract to Padre.
The ROV was equipped with a scanning sonar and video cameras. The 77 ft (24 m) workboat, MV Danny C., owned and operated by Castagnola Tug Services, Santa Barbara, was the ROV support vessel, and ROV and vessel positioning was provided by Fugro Pelagos, Inc. The ROV survey was initiated at OBS-4 and progressed inshore to near the termination point of the Tenera dive survey. The deeper-water segments were surveyed sequentially from OBS-4 to OBS-1.
Video images from the Tenera and Padre surveys were reviewed by Mr. Ray de Wit, Padre Senior Marine Scientist and the discussion and impact assessment provided below are based upon that review.
NEARSHORE OBSERVATIONS On October 16, 2013, the nearshore segment was surveyed by Tenera divers. The nearshore surveyed was approximately 1,800 ft- (560 m-) long, from the 80 ft (24 m) isobath to where the cable entered the PVC conduit along the shoreline of the DCPP intake embayment.
Diver observations, as documented in video collected by Tenera divers, indicate that the seafloor habitat comprises both sedimentary and rocky substrates.
The sedimentary habitat consists of medium to coarse-grain sand, with more coarse material found immediately offshore of the DCPP embayment entrance, in water depths ranging from 59 to 78 ft (18 to 24 m). Finer-grain sediments are prevalent within the embayment.
Substantial drift algae also covered the seafloor inside the embayment breakwaters. A tube-building worm (Diopatra sp.) is common within the sedimentary seafloor habitat along this segment; also present is the bat star (Patiria miniata). Sand waves within this segment range from 1 to approximately 3 in (3 to 8 cm) high. Cable tension was light to moderate within the sedimentary habitat areas, and approximately 50% of the 1,083 ft (330 m) of cable within the sedimentary habitat was buried; depth of natural burial ranged from 1 to 3 in (2.5 to 8 cm). No sediment-associated biota were buried or damaged by the installed cable; however, thick drift algae covered much of the inshore portion of the survey area, precluding direct observations of the cable on the sedimentary seafloor there.
Page 3 of 15 GEO.DCPP.TR.14.04 R0 Appendix E
PG&E Geosciences Department January 31, 2014 (1102-0621)
C:\\USERS\\JKLAIB.PADRE-JENNKLAIB\\DOCUMENTS\\PG&E OBS\\FINAL PGE ROV SURVEY LTR 11-0621 013114.DOC Rock habitat, comprised of boulder/cobble beds and isolated reefs, supported several algae species, including the sea palm (Pterogophora californica), a brown strap kelp (Laminaria setchellii), and occasional giant kelp (Macrocystis pyrifera). Epifauna attached to rocky substrate included bat stars, unidentified solitary corals, at least two species of sea stars (Pisaster giganteus and P. ochraceas), and the strawberry anemone (Corynactis californica),
which were most common on the rocky substrate offshore of the embayment entrance. Rocky substrata within the embayment had sediment cover and supported a less diverse epibiota community. Rockfish (Sebastes spp.) and the convict fish (Oxylebius pictus) were present to common around rock features.
The cable crossed over approximately 755 ft (230 m) of rock habitat, but due to the irregular topography of the substrate, actually contacted rock along approximately 131 ft (40 m).
The cable was laid adjacent to several sea palm plants, but did not appear to have damaged any stipes or holdfasts. No other epibiota were observed to have been crushed or covered by the cable where it touched the rocky substrate.
OFFSHORE OBSERVATIONS
-80 FT ISOBATH TO OBS-4. Observations within this 1.3 mi (2.1m) -long segment were completed on December 6, 2013. The ROV initiated the survey at OBS-4 and followed the cable inshore to approximately the 80 ft (24 m) isobath, where Tenera had terminated the inshore diver observation survey in October 2013. Approximately 4.5 hours5.787037e-5 days <br />0.00139 hours <br />8.267196e-6 weeks <br />1.9025e-6 months <br /> of video were recorded within this segment at a water depth range between 80 and 176 ft (24 and 54 m).
Based on navigational post-plots, approximately 72 ft (22 m) of the cable was not observed by diver or ROV surveys. The 72 ft (22 m) segment was between the inshoremost point of the ROV survey and the offshore terminus of the Tenera diver survey. The segment was within sedimentary habitat, and no rock or other high-relief objects were observed on the scanning sonar image screen.
Seafloor habitats within this segment comprised both sedimentary (silty clay to sand) and rocky (boulder fields and isolated low to moderate relief reefs [1 to 8 ft- [0.3 to 2.4 m-] ), with 1 to 6 in-(2.5 to 15 cm-) high north-south oriented sand waves present where sediment was coarse. Sand waves inshore of the 120 ft (37 m) isobath were smaller and less organized (no linear orientation) than those observed in deeper water. Sedimentary habitat was present along approximately 5,837 ft (1,779 m; 86%) of the segment and rock habitat was observed along 955 ft (291 m; 14 %). OBS-4 was located on a coarse sediment seafloor habitat with sand waves up to 6 in (15 cm) high present (Figure 4).
Within the 955 ft (291 m) of rock habitat crossed within this segment, the cable actually contacted rock substrate for only 92 ft (28 m). The cable was suspended over rock habitat along the remaining distance. While the suspension of the cable was generally less than 1 ft (0.3 m), in two locations the cable was suspended up to 5 ft (1.5 m) between rock features. The lower-relief rock habitat within this segment was covered with a thin veneer of sediment and was relatively depauperate of epibiota, though higher features did support the plumose anemone Metridium giganteus. Other rock-associated epibiota included solitary corals, gorgonian coral (i.e., Muricea sp.), and unidentified hydroids (Figure 5).
Page 4 of 15 GEO.DCPP.TR.14.04 R0 Appendix E
PG&E Geosciences Department January 31, 2014 (1102-0621)
C:\\USERS\\JKLAIB.PADRE-JENNKLAIB\\DOCUMENTS\\PG&E OBS\\FINAL PGE ROV SURVEY LTR 11-0621 013114.DOC No attached macrophytic algae was observed on the rock features within this segment, and juvenile and adult rockfish were present, but not common, around rock features. Observed impacts to epibiota were limited to two Muricea, both of which were under the cable. Common biota observed within the sedimentary habitats included the bat star (Patiria miniata) and two species of seapen (Stylatula elongata and Acanthoptilum sp.). An unidentified burrowing anemone was also present within the sedimentary habitat, and a tube worm (Diopatra ornata) was present to common inshore of the 100 ft. (30 m) isobath. Unidentified octopi, the lingcod (Ophiodon elongatus), and Dungeness crabs (Metacarcinus=Cancer magister) were present within this habitat. No sediment-associated biota was observed to have been directly impacted by the cable, and crabs and lingcod were hiding under the cable where it was suspended between sand waves.
Cable tension within this segment varied from none to moderate; the cable was relatively taut where it was suspended between rock features. Burial depth of the cable within the sedimentary habitat varied from 0 (between the peaks of the higher sand waves) to an estimated 3 in (7.6 cm) (within the silty clay sediment areas). OBS-4 (Figure 4) was located on sedimentary seafloor habitat and appeared to have settled less than 1 ft (0.3 m) into the sandy sediments.
OBS-4 TO OBS-3. Observations within this 4.9 mi- (7.9 km) long segment were completed on December 8, 2013 (poor sea conditions precluded operations on December 7),
with the ROV initiating the survey at OBS-4 and following the cable offshore to OBS-3. A portion of this cable within this segment was loosely laid in a loop with a circumference of approximately 1,290 ft. (393 m). Approximately 2.5 hours5.787037e-5 days <br />0.00139 hours <br />8.267196e-6 weeks <br />1.9025e-6 months <br /> of video were recorded within this segment and the water depth range was from approximately 176 to 340 ft (54 m to 104 m).
Seafloor habitats within this segment were both sedimentary (silty clay) and rocky (low to moderate relief reefs with boulders, 1 to 8 ft [0.3 to 2.4 m] high,). Sedimentary habitat was present along approximately 24,074 ft (7,274 m) (97%) of the cable length within this segment and rock habitat was observed along 742 ft (226 m) (3%). No coarse sedimentary habitat or sand waves were observed within this segment. OBS-3 was located on silty/clay sedimentary seafloor habitat (Figure 6). In addition to the OBS unit, a junction box (also referred to as a splitter box), approximately 11.9 in length and 6.6 in diameter (302 millimeters [mm] by 168 mm), that connects the cable between OBS-4 and OBS-3 was observed within this segment (Figure 7).
Fifty-three ft. (17 m) of rock habitat is contacted by the cable between these two OBS units. Approximately 2.5 mi (4.0 km) northwest of OBS-4, the cable loop described above extends to the northeast and then to the southwest. Within this 1,290 ft-(393 m-) long loop, the cable crosses 551 ft (168 m) of rock habitat and actually contacts the rock for approximately 32 ft (10 m). The seafloor habitat within the remaining cable alignment between the two units is sedimentary with coarse grain material and sand waves present in water depths of 154 ft (47 m) or less and silty/clayey sediment throughout the remainder of the cable corridor.
Rock habitat supported an epibiota similar to that described above; however, rock substrata in water depths of 250 ft (76 m) or more supported the crinioid Florometra sp.
Rockfish, including blue rockfish (Sebastes mystinus), were more abundant within this segment Page 5 of 15 GEO.DCPP.TR.14.04 R0 Appendix E
PG&E Geosciences Department January 31, 2014 (1102-0621)
C:\\USERS\\JKLAIB.PADRE-JENNKLAIB\\DOCUMENTS\\PG&E OBS\\FINAL PGE ROV SURVEY LTR 11-0621 013114.DOC that inshore of OBS-4, but were not common. An aggregation of approximately 100 ratfish (Hydrolagus colliei) was observed near a rock feature at 244 ft (74 m) depth within this segment.
Based on observations, four Metridium were impacted (cut or crossed) by the cable laid across rock habitat within this segment; no other impacts to the rock habitat or associated biota were recorded.
Characteristic sediment-associated macroepibiota included the two aforementioned sea pen species and the plumose sea pen (Ptilosarcus gurneyi). The multi-armed sunstar (Solaster sp.) and the grey tectrabranch (Pleurobranchus sp.) were present but not abundant. One sea pen (Acanthoptilum sp) was buried under the cable within this segment. No other impacts to the sediment-associated biota were observed within this segment.
The cable was approximately 20% buried within the sedimentary substrate. Depth of burial ranged from approximately 1 in (2.5 cm) through the peaks of sand waves to approximately 3 in (7.5 cm) in finer-grained sediments. In fine-sediment habitat, the cable was approximately 50% buried. Within coarse-grain habitat, burial was approximately 10% due to the topography of the sand waves within that habitat. With time, the cable is expected to be completely buried within the silty sediments, but is likely to remain exposed in the coarse-grain habitat where the sediment is subjected to stronger currents.
Tension on the cable ranged from zero (within finer grain sediment habitat) to moderate within the sand wave habitat and where it crossed higher elevation rock features.
OBS-3 TO OBS-2 AND TEMPORARY OBS-2. The cable route from OBS-3 to OBS-2 was also completed on December 8, 2013. Fine sediments characterize the seafloor habitat at the OBS-2 location (Figure 8) and along the 3.0 mi - (4.5 km-) long cable route between OBS-3 and OBS-2; no rock habitat was observed within this area. Similarly, the location where the Temporary OBS-2 was placed comprises fine sediments. Macroepibiota observed within this cable segment was similar to that discussed above, with sea pens (particularly Acanthoptilum sp. and Stylatula elongata) and unidentified octopi being most common. Fish observed on and around the sedimentary seafloor included both long and short-spine combfish (Zaniolepis latipinnis and Z. frenata, respectively), and unidentified flatfish.
Approximately halfway between OBS-3 and OBS-2, in approximately 346 ft (105 m) of water, the former location of Temporary OBS-2 was observed. An approximately 1 ft. (0.3 m) deep and 3 ft (1 m) long depression was recorded; no obvious loss of biota associated with the placement or removal of Temporary OBS-2 was observed.
The cable between the two long-term OBS units within this segment was approximately 15% buried and the cable was under no tension along this entire segment. No biota was observed to have been impacted by the cable within this segment.
OBS-2 TO OBS-1 AND TEMPORARY OBS-1. The cable route from OBS-2 to OBS-1 was completed on December 9, 2013. The seafloor at OBS-1 (Figure 9) and along 2.1 mi- (3.4 km-) long corridor between OBS-2 and OBS-1 is predominantly sedimentary, comprising fine-grain sediments; no coarse-grain sediments were observed within this segment. The epibiota associated with the sedimentary habitat was similar to that discussed above; however, Dungeness crab were more common here than in deeper water areas. No impacts on the Page 6 of 15 GEO.DCPP.TR.14.04 R0 Appendix E
PG&E Geosciences Department January 31, 2014 (1102-0621)
C:\\USERS\\JKLAIB.PADRE-JENNKLAIB\\DOCUMENTS\\PG&E OBS\\FINAL PGE ROV SURVEY LTR 11-0621 013114.DOC sediment-associated biota related to the placement of the cable or the temporary and permanent OBS units within this segment were observed.
A single, low-relief (approximately 1 ft. [0.3 m] high) 39 ft.- (12 m-) long rock reef was observed approximately half-way between the two OBS units, at approximately 255 ft. (78 m) depth. Most of the rock was sediment-covered, but two Metridium were observed attached to the substrate. The cable contacted rock substrate for 5 ft. (2 m) of the rock feature, however no cable-associated impacts to the rock-associated epibiota were observed.
The former location of Temporary OBS-1 was observed, however no obvious depression or other seafloor scarring at or around that location was recorded. The seafloor habitat at the location of Temporary OBS-1 was fine-grain sediment, and no impacts to the sediment-associated biota at the site were observed.
Approximately 10% of the cable within this segment was buried in the silty sediment and no cable tension, including where it crossed the low-relief rock feature discussed above, was apparent.
ASSESSMENT OF IMPACTS This project-specific environmental document indicates that an estimated 1.3 mi. (2.1 km) of cable was expected to cross rocky substrate, and that some undetermined number of organisms could be affected. Based on the review of video footage from the as-laid diver and ROV surveys, approximately 0.47 mi (0.76 km) of rocky substrate was crossed, and approximately 313 ft. (95 m) of cable was observed to be in contact with rocky substrate. As a result of that contact, two sea fans (Muricea sp.) and four anemones (Metridium giganteum) were impacted. No physical damage to the rocky substrate (i.e., breaking of rock) was recorded in the video from the two surveys. Although the cable is moderately taut across some of the rock features, the size and relative flexibility of the cable is not expected to result in future damage to the rocky substrate.
Within the sedimentary habitat areas, one sea pen (Acanthoptilum sp.) was crossed by the cable in the sedimentary habitat. It is likely that some additional macroepibiota were under the long-term OBS units when they were placed and have, therefore, been crushed. Based on the density of those organisms and the size of the OBS units, it is expected that between 10 and 20 seapens and/or anemones were affected. The cable did create a narrow, 2 in. (5 cm) depression in the finer, clayey sediments; that depression is expected to fill within one to two years. In the coarse-grained sediments, characteristic of areas where near-bottom currents are stronger, no habitat alteration was observed.
All long-term OBS units are on sedimentary habitat and the current cable alignment appears to have avoided rocky substrate to the greatest extent possible. Impacts to the seafloor appear to be minimal and less than was originally estimated in the environmental document.
If you should have any questions regarding the above information and/or require additional information, please contact me at (805) 683-1233, ext. 4, or spoulter@padreinc.com.
Page 7 of 15 GEO.DCPP.TR.14.04 R0 Appendix E
PG&E Geosciences Department January 31, 2014 (1102-0621)
C:\\USERS\\JKLAIB.PADRE-JENNKLAIB\\DOCUMENTS\\PG&E OBS\\FINAL PGE ROV SURVEY LTR 11-0621 013114.DOC Sincerely, PADRE ASSOCIATES, INC.
Simon A. Poulter Manager, Environmental Sciences Group Attachments: Attachment A - Figures c: Kris Vardas (PG&E)
Page 8 of 15 GEO.DCPP.TR.14.04 R0 Appendix E
C:\\USERS\\JKLAIB.PADRE-JENNKLAIB\\DOCUMENTS\\PG&E OBS\\FINAL PGE ROV SURVEY LTR 11-0621 013114.DOCC:\\USERS\\JKLAIB.PADRE-JENNKLAIB\\DOCUMENTS\\PG&E OBS\\DRAFT PG&E ROV SURVEY LTR 11-0621 013014.DOCX ATTACHMENT A FIGURES Page 9 of 15 GEO.DCPP.TR.14.04 R0 Appendix E
PG&E Geosciences Department January 31, 2014 (1102-0621)
C:\\USERS\\JKLAIB.PADRE-JENNKLAIB\\DOCUMENTS\\PG&E OBS\\FINAL PGE ROV SURVEY LTR 11-0621 013114.DOC
- A1 -
Figure 1. Region and Site Seafloor Habitats with Installed OBS and Cable Locations Page 10 of 15 GEO.DCPP.TR.14.04 R0 Appendix E
PG&E Geosciences Department January 31, 2014 (1102-0621)
C:\\USERS\\JKLAIB.PADRE-JENNKLAIB\\DOCUMENTS\\PG&E OBS\\FINAL PGE ROV SURVEY LTR 11-0621 013114.DOC
- A2 -
Figure 2. Installed OBS and Cable Locations with Marine Protected Area Page 11 of 15 GEO.DCPP.TR.14.04 R0 Appendix E
PG&E Geosciences Department January 31, 2014 (1102-0621)
C:\\USERS\\JKLAIB.PADRE-JENNKLAIB\\DOCUMENTS\\PG&E OBS\\FINAL PGE ROV SURVEY LTR 11-0621 013114.DOC
- A3 -
Figure 3. OBS and Cable As Laid Location with NOAA Nautical Chart Page 12 of 15 GEO.DCPP.TR.14.04 R0 Appendix E
PG&E Geosciences Department January 31, 2014 (1102-0621)
C:\\USERS\\JKLAIB.PADRE-JENNKLAIB\\DOCUMENTS\\PG&E OBS\\FINAL PGE ROV SURVEY LTR 11-0621 013114.DOC
- A4 -
Figure 4. Video-Still of OBS-4 with Deployment Bridle (Water Depth 174 ft. [53 m])
Figure 5. Video-Still of Cable Crossing Rock Feature and Suspended Between Rock Features (Water Depth 175 ft. [53 m])
Page 13 of 15 GEO.DCPP.TR.14.04 R0 Appendix E
PG&E Geosciences Department January 31, 2014 (1102-0621)
C:\\USERS\\JKLAIB.PADRE-JENNKLAIB\\DOCUMENTS\\PG&E OBS\\FINAL PGE ROV SURVEY LTR 11-0621 013114.DOC
- A5 -
Figure 6. Video-Still of OBS-3 and Installation Bridle (Water Depth 340 ft. [104 m])
Figure 7. Video-Still of Junction Box Between OBS Units 4 and 3 (Water Depth 252 ft. [77m])
Page 14 of 15 GEO.DCPP.TR.14.04 R0 Appendix E
PG&E Geosciences Department January 31, 2014 (1102-0621)
C:\\USERS\\JKLAIB.PADRE-JENNKLAIB\\DOCUMENTS\\PG&E OBS\\FINAL PGE ROV SURVEY LTR 11-0621 013114.DOC
- A6 -
Figure 8. Video-Still of OBS-2 and Installation Bridle (Water Depth 330 ft. [101 m])
Figure 9. Video-Still of OBS-1 and Installation Bridle (Water Depth 210 ft. [64 m])
Page 15 of 15 GEO.DCPP.TR.14.04 R0 Appendix E
APPENDIX F Post-Deployment Nearshore Diver Survey Page 1 of 7 GEO.DCPP.TR.14.04 R0 Appendix F
Diablo Canyon Power Plant OBS Cable Post-Deployment Diver Survey November 14, 2013 Prepared for:
Prepared by:
Ms. Marcia McLaren Tenera Environmental Pacific Gas & Electric Co.
San Francisco, CA 141 Suburban Rd., Ste. A2 San Luis Obispo, CA 93401 805.541.0310 Purpose This report describes the post-deployment survey findings for the nearshore section of the Diablo Canyon Power Plant (DCPP) Ocean Bottom Seismometer (OBS) cable. The nearshore section of the cable starts at the -80 ft (-24 m) MLLW depth contour outside the DCPP intake cove and passes through the intake cove to where it rises up the intertidal revetment through a conduit on the northeast shore of the intake cove (Figure 1). From there the cable passes under a road and terminates inside the data processing lab.
The nearshore section was surveyed by divers using SCUBA because the shallow area cannot be surveyed by remote operated vehicles (ROVs), due to the presence of kelp and rock pinnacles that can tangle the ROV tether and cable. The divers collected latitude/longitude coordinates of the as-built nearshore cable alignment, and completed underwater videography to document the habitats and species along the cable. A GIS shapefile with the coordinates of the cable alignment and the video are provided as additional deliverables.
Prior to the cable deployment, the habitats and predominant benthic species along the planned cable route of the nearshore section were documented in surveys completed by Tenera divers on May 17-20, 2011.1 The nearshore section of the OBS cable was subsequently deployed through the intake cove on July 26, 2013. Tenera divers assisted with deploying and positioning portions of the nearshore cable section to its final (as-built) alignment. The post-deployment survey of the nearshore cable section was then completed on October 16, 2013. The following sections of the present report describe the survey methods and findings.
1 Tenera Environmental. 2011. Ocean Bottom Seismometer Cable Landing, Habitat Characterization Study, Diablo Canyon Power Plant, May 27, 2011.
Page 2 of 7 GEO.DCPP.TR.14.04 R0 Appendix F
Methods The OBS cable post-deployment survey of the nearshore section was completed on October 16, 2013. Seas were calm with 1-2 ft (0.3-0.6 m) swell, and winds were light. Underwater horizontal visibility was approximately 20 ft (6 m).
The survey began at a starting depth of approximately -76 ft (-23 m) MLLW, which was approximately 230 ft (70 m) further offshore from the outermost location of the pre-deployment survey. From there the survey progressed inshore (Figure 1). The submerged cable was videotaped using a Sony Handycam Model HDR-CX550V digital video camera inside a Light and Motion Bluefin 550 waterproof housing. At the same time, the divers towed a Garmin ETrex Legend GPS unit attached to a surface float with the tether line held taught to keep the GPS unit directly above the divers. This provided a trackline of latitude/longitude coordinates for the Figure 1. OBS cable nearshore section through the DCPP intake cove showing the as-built alignment (green) and planned alignment (red) and divided into three segments based on substrate habitats crossed. Running times of the video camera are shown for every 4-minutes.
Page 3 of 7 GEO.DCPP.TR.14.04 R0 Appendix F
nearshore cable section (Figure 1). The GPS unit was set to record at 3-second intervals. The GPS and camera times were synchronized by correcting for the time offset between the two units (by videotaping the time display of the GPS unit). This allowed the video images to be synced with their locations along the cable route.
Results and Discussion The total cable distance surveyed from the -76 ft (23 m) MLLW depth outside the intake cove to the intertidal revetment at the shoreline was approximately 1,837 ft (560 m). The total run time of the underwater video was 39 minutes 46 seconds. The divers were able to survey this entire distance in a single dive, and thus the videotaping and position recordings ran continuously and were never interrupted.
The as-built OBS cable alignment of the nearshore section determined by towing a surface GPS unit over the cable appears in Figure 1. The actual alignment, however, is likely smoother than the line shown in Figure 1, due to the GPS unit not being able to be kept directly above the video divers at all times. It was difficult to keep the GPS unit directly above the video divers when they were in deep water, in the intake cove entrance area where currents were strong, and where surface canopy kelp and drift kelp became tangled with the GPS tether line.
Overall, the as-built cable alignment of the nearshore section closely matches the planned alignment (Figure 1); the cable passes through the same general zones described in the pre-deployment survey that were differentiated based on habitat and species characteristics. The underwater video reveals the as-built cable laying across three types of substrate habitats: an expansive sand flat mainly outside the intake cove; areas of mixed substrates (bedrock, boulder, cobble, gravel, sand) inside the intake cove; and areas of mainly bedrock and boulders where the cable approaches the intertidal revetment and comes to shore (Figure 1, Table 1).
Table 1. Approximate lengths (m) of the nearshore OBS cable crossing over three types of substrates.
Segment Video Run Time (minutes-seconds)
Depth Range (m MLLW)
Sand Flat (m)
Mixed Substrates (m)
Rocky (m)
Comments 1
00:00-08:30 21-23 90 Largely barren sand flat. Occasional low-relief rocks covered with bat stars (Patiria miniata).
2 08:30-34:30 6-21 385 Giant kelp (Macrocystis pyrifera),
subcanopy kelps (Pterygophora californica, Laminaria setchellii), sea stars (P. miniata, Pisaster spp.), and ornate tube worms (Diopatra ornate) prevalent in general area. Red and green algal understory prevalent in shallower water.
3 34:30-39:46 0-6 85 Larger proportion of bedrock and boulders, relative to sand.
Page 4 of 7 GEO.DCPP.TR.14.04 R0 Appendix F
The cable lengths associated with the substrate habitats in Table 1 are approximate, and would be expected to change seasonally due to sand accretion and attrition associated with natural sediment transport in the area.
There were no indications of habitats or biota having been impacted from the cable installation.
The cable was deployed very close to the planned route, and there were no observations of overturned rocks, damaged kelp, or injured or dislodged invertebrates, which would indicate potential impacts due to the deployment of the cable. Furthermore, the divers shifted the alignment of the cable in areas where movement may have resulted in impacts. The cable is small in diameter (approximately 0.5 in. [1.3 cm]), and was already settling and becoming buried under sand in many areas. It had been 73 days since the time the cable was deployed.
Representative video images of the nearshore cable section follow.
Page 5 of 7 GEO.DCPP.TR.14.04 R0 Appendix F
Segment 1 at 00:00 run time. Diver is holding the tether of the GPS unit that is directly above.
Segment 1 at 00:07 run time showing cable passing next to rock covered with bat stars.
Segment 1 at 00:40 run time with cable buried under sand with tie-wrap protruding.
Segment 1 at 07:20 run time with cable over sand.
Segment 2 at 16:27 run time with subcanopy kelps attached to rocks next to cable.
Segment 2 at 20:46 run time with cable settling between mats of ornate tube worms.
Page 6 of 7 GEO.DCPP.TR.14.04 R0 Appendix F
Segment 2 at 20:59 run time.
Segment 2 at 27:41 run time.
Segment 2 at 29:30 run time with cable crossing over a sand pocket area.
Segment 2 at 32:24 run time.
Segment 2 at 32:32 run time with cable on heavily silted boulder.
Segment 2 at 33:56 run time Segment 3 at 38:50 run time.
Segment 3 at 39:38 run time with cable in conduit running up shore revetment.
Page 7 of 7 GEO.DCPP.TR.14.04 R0 Appendix F
APPENDIX G Noise Survey Page 1 of 18 GEO.DCPP.TR.14.04 R0 Appendix G
GURALP SYSTEMS LIMITED, 3 MIDAS HOUSE, CALLEVA PARK, ALDERMASTON, READING, RG7 8EA, UK.
TELEPHONE: +44 118 9819056 FAX: +44 118 9819943 guralp@guralp.com Horst Rademacher Chris Pearcey Giorgio Mangano Deployment of two Portable OBS off Point Buchon, CA 10 Feb 14 Version 2.1 GURALP SYSTEMS LIMITED, REGISTERED OFFICE, 3 MIDAS HOUSE, CALLEVA PARK, ALDERMASTON, READING, RG7 8EA REGISTERED IN ENGLAND No. 2199239. VAT REGISTRATION No. 491 4657 20.
Page 2 of 18 GEO.DCPP.TR.14.04 R0 Appendix G
Portable OBS In the late summer and early fall of 2013 Guralp Systems Ltd. (GSL) deployed two autonomous portable Ocean Bottom Seismometers (P-OBS) near Point Buchon, CA. Their deployment was part of a wider OBS based system for monitoring two off-shore faults, the Hosgri-and the Shoreline-Fault in the waters off Central California. Initially we had planned to deploy each sensor for two weeks each at two different locations. However, for operational reasons, each sensor was left in its first location for more than three months and not deployed at a second location. In this report, we will give an initial description of the performance of the portable instruments and assess the data they collected. This report is meant as a survey and not as an exhaustive scientific analysis of the data gathered by the OBS.
1.
The instruments Fig. 1: The two instruments in their initial pre-deployment configuration.
The glass spheres are covered with orange plastic protectors Each instrument consists of a frame, two sealed glass spheres, the sensor package, the anchor weights and peripheral equipment (figure 1). The glass spheres contain the batteries, the digitizer and the data storage device. They also provide the buoyancy necessary for the recovery of the instruments. The peripheral equipment includes an acoustic transponder and various recovery aids, i.e. a strobe light, a GPS receiver and an FM transmitter.
The sensor package is mounted in the center underneath the frame (see figure 2). It contains a standard CMG-40T feedback seismometer with a flat frequency response between 60 sec and 80 Hz and a sensitivity of 2000 V/[m/sec]. The sensor is housed in a glass sphere which in turn is contained in a stainless steel frame.
Fig. 2: Sensor mounted in center underneath the frame Version 2.1 2/10/2014 Page 2/17 Page 3 of 18 GEO.DCPP.TR.14.04 R0 Appendix G
Portable OBS Figure 2 also shows two black cylinders at the bottom of the frame. These are the original anchor weights, which are made of ABS pipes filled with concrete. They can be released by an acoustic signal given to the transponder on top of the frame (black round canister in figure 1).
2.
Deployment and Recovery 2.1 The Procedures Because of restrictions set by the State of California during the permitting process for the wider OBS project, we were not able to deploy the two portable OBS in the usual manner. During a common type of deployment one heaves an instrument over board of the deployment vessel, unhooks it from the winch cable and lets it free fall to the sea floor under its own weight. The recovery is initiated by an acoustic signal given from the recovery vessel. Upon receiving this signal through its transponder, the instrument releases itself from the anchoring weights and floats to the sea surface under its own buoyancy. Once at the surface, it is recovered manually by the deck crew of the vessel. As a consequence, the anchor weight, usually an environmentally benign piece of heavy steel or concrete, is left on the sea floor. Because the State permit did not allow us to leave anything behind on the sea floor, we changed the deployment and recovery procedures for this project.
2.1.1 Deployment Instead of letting the instruments sink to the ocean floor under their own weight, we lowered each of them by winch and wire rope from the deck of the ship. In addition each instrument was connected by a line to a clump weight. The length of this line was about twice the water depth at the deployment site. We attached a second line to the clump weight which had buoys and floaters at the other end. The floaters were needed to mark the location of the portable OBS for the recovery operation. In order to prevent the instruments from being dragged over the sea floor by ocean currents or maritime operations, we added a heavy anchor chain to the frame (see figure 3). The chain increased the weight of the instruments considerably and actually made the deployment more stable.
Fig. 3: One of the portable OBS shortly before deployment. Note the chains added to increase stability of the OBS.
2.1.2 Recovery We recovered the instruments in early November 2013 after each had spent more than 100 days on the sea floor. One of the instruments (Temp-1) had the buoys and floaters still attached to the line connected to the clump weight. After recovering the floaters, we hooked this line to a winch and pulled the clump weight on deck. We then disconnected the line between the clump weight and the sensor frame from the clump weight, attached it to the winch and pulled the instrument up.
Version 2.1 2/10/2014 Page 3/17 Page 4 of 18 GEO.DCPP.TR.14.04 R0 Appendix G
Portable OBS The buoys and floaters orginally attached to Temp-2 had gotten lost during the deployment period. In order to recover this instrument, we used an ROV. With its help, we could attach a carabine hook and a line to the instrument's frame (see figure 4). The ROV brought the line to the sea surface and handed it over to the recovery vessel. Once this line was secured on the deck of the recovery vessel, we attached it to the winch and pulled up the instrument. In the last step, we recovered the clump weight, using the line between it and the sensor frame, thus satisfying the requirement to leave nothing behind on the sea floor.
Fig. 4: Instrument Temp-2 on the sea floor shortly before recovery in a photo taken by the ROV. The blue hook in the foreground is attached to the manipulator arm of the ROV.
It is used to hook into the shackle at the center of the frame.
Note the fish on the sea floor and sea anemone (Metridium farcimen), which had taken up residence at the bottom of the instrument during its 104 days on the sea floor.
2.2 Deployment Duration and Locations Table 1 gives the data for the deployment duration and the locations of the instruments.
Name GSL S/N Date Date Days Latitude Longitude Water depth deployed recovered deployed decimal ON decimal OW
[m]
2013 2013 (drop point)
(drop point)
Temp-1 GSL00-POBS 27 Jul 7 Nov 102 35.267477 120.945115 70 Temp-2 6217C-1616 25 Jul 7 Nov 104 35.236093 120.950308 106 Table 1 During the recovery process the ROV found each of the two instruments located on the ocean floor within a distance of less than 30 m from the drop points at the sea surface. The surface locations were measured upon deployment by GPS by the navigator on the deployment vessel. Because this difference is very small, we decided to use the drop point GPS coordinates as the actual locations of the instruments. The error introduced by this difference is minute compared to the other, larger uncertainties usually dealt with when interpreting seismic data.
Fig. 5: A Google Earth map of the locations of the two portable OBS Temp-1 and Temp-2 with respect to the shore station, labelled DCPP.
OBS-4 is the location of the only other instrument of the wider OBS network operating during the time of the deployment of the portable OBS units.
Version 2.1 2/10/2014 Page 4/17 Page 5 of 18 GEO.DCPP.TR.14.04 R0 Appendix G
Portable OBS 3.
The Data In this chapter I will give an evaluation of the data collected by the two instruments. I will focus on various types of noise in different frequency bands and will show the recordings of several earthquakes. This evaluation is not meant to be, and does not replace, an exhaustive scientific analysis of the recordings.
In the time series shown in the some of following figures, the green line always represents the vertical, red the first horizontal component and blue the horizontal component perpendicular to the first. What I call in this chapter the first horizontal component would normally be referred to as the N/S component, with the other being the E/W component. However, because we do not know the orientation of the sensors on the sea floor, we cannot refer to the horizontal components by their common nomenclature. Unless otherwise noted, the data shown are always the unfiltered original broadband recordings. The traces in each figure are scalled to the same common factor. The time marks in UTC are always along the top of the figure with the data shown in the upper right hand corner.
The color scheme for the spectrograms shown in other figures in this chapter goes from blue (least intense) to red and even deep purple (most intense). The colours represent relative and not absolute intensities. Unless otherwise noted all figures showing data are generated using the program "Scream" which stands for "Seismometer Configuration, REal time Acquisition and Monitoring". Scream is a Windows and Linux application developed by Guralp Systems Ltd.
and distributed with its digitizers. It allows to monitor, configure and record data from an entire seismic network, including both local and remote sites.
3.1 Data Availability and Timing Drift Because the duration of the actual deployment of the two senors was much longer than anticipated (see note in introductory paragraph), both systems filled up their respective memories towards the end of the deployment period and stopped recording afterwards. Table 2 shows the periods of data availability.
Name GSL S/N Recording Recording Start (UTC)
End (UTC)
Temp-1 GSL00-POBS 25 Jul 14, 23:25 29 Oct 14, 14:47 Temp-2 6217C-1616 27 Jul 14, 17:42 3 Nov 14, 06:30 Table 2 During the recording period as decribed in table 2, the collected data are complete without any gaps or component failures within the instruments. This corresponds to a data availability of 100 percent.The total amount of data collected during the deployment by these two instruments was more than 33 GByte in Guralp's own GCF Format. In addition both sensors, the digitizers and Version 2.1 2/10/2014 Page 5/17 Page 6 of 18 GEO.DCPP.TR.14.04 R0 Appendix G
Portable OBS data loggers to which they were connected performed nominally over the whole deployment period. This lead to an excellent data quality without any anomalies.
As is typical for the deployment of portable OBS, these two units were not connected to a timing source during their deployment on the sea floor. We synchronized each digitizer's internal clock to GPS shortly before deployment and then again immediately after recovery. We found that the drift of the internal clocks was less than 300 msec in both cases. This corresponds to less than 3 msec a day assuming a linear drift. Because the sampling rate was set at 200 samples per second (sps) - one sample every 5 msec -, this clock drift corresponds to less than one digitisation interval per day. As the data evaluation presented here is only initial, I chose to ignore this very small clock drift.
However, depending on the depth and thoroughness of a future seismic analysis of the data collected by the two protable OBS, the overall drift of 300 msec during the whole deployment duration may have to be compensated by a linear drift correction of 3 msec/day.
3.2 Noise Even during the discussion and planning phases for the deployment of the portable OBS, we expected to see a lot of noise in their recordings for several reasons, among others:
- The instruments were deployed in very shallow water of no more than 106 m water depth (see table 1). They were therefore under the strong influence of wave action at the sea surface.
Typically OBS are deployed in much deeper waters.
- In contrast to the cabled OBS deployed in the wider network, the portable OBS described here were not covered by heavy concrete domes, hence they were much more exposed to waves and currents.
- As seen in figure 4, during their deployment the portable OBS became a habitat for sea life in the otherwise barren sand plains of the ocean bottom in the deployment area. Because each instrument's seismometer housing is exposed in the OBS frame, such sea life can easily touch the sensors and thereby generate noisy disturbances.
In the following, I will show and discuss examples of several kinds of noise. This discussion is by no means exhaustive as it only allows a glimpse into the large amounts of data gathered here.
3.2.1 Short Period Noise The short period seismic noise during the deployment period was highly variable, both in time as well as in shape and amplitude. To show some typical features I have randomly chosen a three hour window on 15 Oct 13 between 00:00 and 03:00 UTC for analysis. In the following three figures (figure 6-8) I always show in the top section the same three hour long unfiltered time series of the vertical component of Temp-2 (green line). The bottom section of each of shows a spectrogram of this time series in various spectral bands. A spectrogram is a visual representation of the of frequencies contained in the time series. In contrast to a spectrum or a power spectgral density plot, the spectogram shows how the amplitudes of the various vary over time.
Version 2.1 2/10/2014 Page 6/17 Page 7 of 18 GEO.DCPP.TR.14.04 R0 Appendix G
Portable OBS Fig. 6: Overview of the noise recorded by the vertical component of Temp-2 (green line)over three hours on 15 Oct 13. The spectrogram scale on the right shows shows the amplitudes in the frequency band up to 100 Hz, the Nyquist frequency determined by the sampling rate of 200 samples per second.
Among the notable feature in the spectrogram are
- a continuous hum with a frequency above 80 Hz and the
- waxing and waning bands of noise between 10 and 30 Hz.
Fig. 7: The spectrogram of the high frequency hum in more detail. The time series on top is again the noise recorded by the vertical component of Temp-2 (green line)over three hours on 15 Oct 13. The spectrogram shows the frequency band between 80.5 and 85 Hz.
Version 2.1 2/10/2014 Page 7/17 Page 8 of 18 GEO.DCPP.TR.14.04 R0 Appendix G
Portable OBS As can be seen in figure 7, the hum has a frequency of about 82.6 Hz. It is rather intense until about 01:40 UTC and then becomes more diffuse. Such pattern of sharper lines waning into a more diffuse pattern at this frequency can be seen in the data almost every day. The same randomly oscillating pattern can be seen The spectrogram of the high frequency hum is shown in more detail in figure 7. It has a frequency of about 82.6 Hz. It is rather intense until about 01:40 UTC and then becomes more diffuse. Such pattern of sharper lines waning into a more diffuse pattern at this frequency can be seen in the data almost every day.
The same randomly oscillating pattern can be seen almost daily in the broader noise in the band between 10 and 30 Hz, as shown in detail in the spectrogram in figure 8. Note that the most intense noise is at 12, 16 and 24 Hz respectively.
Fig. 8: Same three hour time window as in the previous two figures, with the spectrogram showing the frequencyy band up to 33 Hz. One can see diffuse noise waxing and waning at frequencies around 12, 16 and 24 Hz.
Given the fact that there are no known seismic sources with such characteristics in the deployment area, I assume that the two features shown above are sound waves from distant sources travelling through the water. They either cause the vibration of the instruments directly, or through coupling with the surrounding sea floor.
Version 2.1 2/10/2014 Page 8/17 Page 9 of 18 GEO.DCPP.TR.14.04 R0 Appendix G
Portable OBS 3.2.2 Long Period Noise While the short period noise seems to dominate in figure 6, the most intense noise recorded by the two portable OBS actually has much lower frequencies. In contrast to the short period noise, the noise at longer periods is not nearly as variable. For the analysis of the long period noise I again have randomly chosen a three hour time window between 15:00 and 18:00 UTC on 8 Aug 13.
Fig. 9: The two panels show the same three hour time window recorded on 8 Aug 13 between 15 and 18 UTC on a horizontal component of Temp-1 (left panel) and Temp-2 (right). The red and blue lines are the respective time series. The bottom of each panel shows the spectrogram for each time series in the frequency band between 0.05 and 0.8 Hz (20 sec to 1.25 sec period).
While the diffuse band of yellow and red colours in figure 9 indicate some noise energy between 0.4 and 0.5 Hz (2.5 to 2 sec period), the dominant band has an even lower frequency of below 0.1 Hz (10 sec period).
The cause for this noise becomes clear when comparing the seismic noise data shown in figure 9 with the recordings of the differential pressure gauge (DPG) installed on OBS-4. As mentioned before, OBS-4 was the only station of the wider network operating during the deployment of the two portable instruments.
Version 2.1 2/10/2014 Page 9/17 Page 10 of 18 GEO.DCPP.TR.14.04 R0 Appendix G
Portable OBS Fig. 10: The black line shows the time series of the DPG recordings on 8 Aug 13 between 05:30 and 23:00 UTC on 8 Aug 13. This includes the three hours (15:00 - 18:00) shown in figure 9. The spectrogram in the bottom panle shows the frequency band between 0.02 and 0.8 Hz (50 - 1.25 sec)
Similar to figure 9, we see in figure 10 a band of diffuse energy around 2 sec period and the dominant energy band (purple colour) at the bottom at about 14 sec period. The DPG records changes of water pressure acting on the OBS. The main cause for these changes in the shallow depth at which all instruments of this OBS network are deployed are changes in the hydrostatic pressure due to ocean waves travelling over the deployment area. The diffuse band at about 2 sec represents waves driven by local winds, while the more intense band at 14 sec is caused by the longer period ocean swell generated by distant storms.
Fig. 11: Energy density spectrum of the ocean waves as measured by the waverider buoy 076 for 8 Aug 15 at around 16:00 UTC. The data were taken from this website:
http://cdip.ucsd.edu/?nav=historic&stn=076&stream=p1&xitem=stn_home&sub=data Version 2.1 2/10/2014 Page 10/17 Page 11 of 18 GEO.DCPP.TR.14.04 R0 Appendix G
Portable OBS This observation is corroborated by data from waverider buoy 076, a Datawell Mk3 directional buoy operated by PG&E, located in 22 m deep water betweeen OBS-4 and the inlet of DCPP. As can be seen in figure 11 the dominant wave period for 8 Aug 13 at around 16:00 UTC is at 14 sec, the same period which we observed in the seismic data (figure 9) and with the DPG (figure 10).
The change in hydrostatic pressure exerted by these two types of ocean waves causes the sea floor to tilt slightly, which is recorded by the horizontal sensors of the portable OBS. The long period noise shown in figure 9 is therefore a direct consequence of the wave action at the sea surface.
How strong the influence of the swell height on the long period recording is, can be judged when comparing periods of high ocean swell with phases of low ocean swell. Again, using data from waverider buoy 076, during the deployment window the highest swell with a maximum wave height of 5.5 m occured on 30 Sep 13 at around 15:30 UTC. The lowest swell with a maximum wave height of 1.1 m happend on 7 Aug 13 at around 5:20 UTC.
Fig. 12: Power spectral density plots for the same horizontal components of Temp-2. The top panel shows the noise spectrum (solid blue line) during the time of minimum swell (7 Aug 13) The bottom panel shows the noise during the time of maximum swell (30 Sep 13). Both panels are scaled to the same factor. In each of the panel, the dotted blue line represents to USGS low noise, the dotted red line the high noise model.
Version 2.1 2/10/2014 Page 11/17 Page 12 of 18 GEO.DCPP.TR.14.04 R0 Appendix G
Portable OBS As can be seen in figure 12 the seismic noise is between 5 and 25 dB higher during the period of highest swell (lower panel) compared to the day of lowest swell (upper panel).
This long period noise generated by the ocean swell is by far the most dominant noise in the data.
How strong this noise is, became ultimately clear when the strongest teleseismic earthquake occured during the deployment period, the Mw=7.7 event in Pakistan on 24 Sep 13 at 11:29 UTC.
In figure 13 I show the recordings for both portable OBS during the time when the arrivals of the different seismic waves are expected in the area. Despite the application of various filters, neither the P-nor the S-wave arrivals can be seen. Even the surface waves of this event, which are well recorded by other broadband stations in Central California, are masked by the swell noise.
Fig. 13: The recordings of the three components of Temp-2 (upper three traces) and of Temp-1 (lower three traces) during the very two hour time window on 24 Sep 13, when the onsets of the Pakistan earthquake were expected.
While there is a strong correlation of recorded seismic noise with wave heights (see figure 12), we found no evidence in this survey, that changes in the ocean tides had any influence on the seismic noise. This is most likely due to the fact, that the lower frequency limit of the sensors is 60 sec, which is way above the typical tidal periods of 12 and 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> respectively.
Version 2.1 2/10/2014 Page 12/17 Page 13 of 18 GEO.DCPP.TR.14.04 R0 Appendix G
Portable OBS 3.2.3 Artifical Noise The noise described in the previous sections can be seen with various intensities almost daily on both portable OBS simultaneously. This is an indication that its source is not in the immediate vicinity of one of the sensors but that the noise originates further away. There are however many noise recordings, which can only be seen on one of the instruments. One such example is shown in figure 14.
Fig. 14: A 70 min long time window on 23 Aug 13 from 17:20 to 18:30 UTC. The top three traces are the three components of Temp-2, the bottom three are the recordings of Temp-1.
During the first 30 min the data of Temp-2 show typical seismic noise dominated by the ocean swell. However, around 17:46 UTC this pattern changes abruptly. The later sections of the horizontal seismograms of Temp-2 are dominated by strong pings and peaks, which are clearly absent on the respective traces of Temp-1. I therefore conclude, that the change in pattern has a local source at or near Temp-2. It is very likely that it is caused by animals rumaging in the area as for example seen in figure 4. The crew of the ROV, which assisted us during the recovery of the portable OBS, reported numerous animal sightings, among them a large star fish crawling over the instruments.
3.3 Seismic Events Recorded by the Instruments The main purpose for deploying the OBS network in this area is to monitor the microseismic activity on two faults offshore of Central California, the Hosgri-and the Shoreline-Fault. I will therefore refrain from showing the recordings of teleseismic events by the two instruments, particularly in light of the dominant effect of the swell generated noise in the longer period (see section 3.2.2). Instead I will concentrate on a few examples of local earthquakes.
Version 2.1 2/10/2014 Page 13/17 Page 14 of 18 GEO.DCPP.TR.14.04 R0 Appendix G
Portable OBS In order to find relevant local earthquakes in or near the deployment area I accessed the ANSS catalog through the Northern California Earthquake Data Center (NCEDC). Except for the seismic activity along the San Andreas Fault and in the aftershock area of the 2003 San Simeon earthquake further inland, there are in fact very few earthquakes within a 100 km radius around the deployment area. The are even fewer offshore quakes. The earthquakes used in this section are listed by date in table 3.
Event Date Time Latitude Longitude Depth Ml Distance Distance 2013 (UTC) decimal ON decimal OW (km) or Md to Temp-1 to Temp-2 1
17 Aug 10:01:02 35.19 120.9125 3.7 1.9 9.5 6.5 2
24 Aug 01:16:31 34.5667 120.9567 3.2 4.1 73.0 76.0 3
7 Sep 21:51:01 35.0753 120.9422 2.8 1.3 21.4 17.9 Table 3 3.3.1 Ml=4.1 off Pt. Arguello (Event 2 in table 3)
The strongest local earthquake during the deployment period occured offshore on 26 Aug 13 at 01:16:30 UTC about 30 km W of Point Arguello. It had a Ml of 4.1. The epicentral distances to Temp-1 and Temp-2 are 76 and 73 km respectively with the seismic waves arriving at the station almost directly from the S. Figure 15 shows the recordings of the two portable OBS (top six traces) compared to the recording of OBS-4 (bottom three traces). In figure 16 I have zoomed in on the P-onset of the same three stations, which are sorted by distance from the source.
Fig. 15: Recordings of the Point Arguello earthquake on the respective three components of Temp-1 (top three traces), Temp-2 (middle) and OBS-4 (bottom). 40 sec of data shown.
Version 2.1 2/10/2014 Page 14/17 Page 15 of 18 GEO.DCPP.TR.14.04 R0 Appendix G
Portable OBS Fig 16: P-onsets of the Point Arguello earthquake shown on the vertical components of Temp-1 (top),
temp-2 (middle) and OBS-4 (bottom). 15 sec of data shown 3.3.2 Md=1.9 on the Hosgri Fault (Event 1 in table 3)
The closest local earthquake during the deployment period occured on the Hosgri Fault WSW of DCPP on 17 Aug 13 at 10:01:02 UTC. It had a Md of 1.9 and a depth of 3.7 km. The epicentral distances to Temp-1 and Temp-2 are 9.5 and 6.5 km respectively. Figure 17 shows the recordings of the two portable OBS (bottom six traces) compared to OBS-4 (top three traces). Note that the P-onset is very clear on all three vertical components, while the S-onset is less clear on the horizontals of Temp-1, the most distant station.
Fig. 17: Event on the Hosgri Fault as recorded by the three respective components of OBS-4 (top), Temp-2 (middle) and Temp-1 (bottom) 8 sec of data show.
Version 2.1 2/10/2014 Page 15/17 Page 16 of 18 GEO.DCPP.TR.14.04 R0 Appendix G
Portable OBS 3.3.3 Md=1.3 about 16 km WSW of DCPP (Event 3 in table 3)
This event occured on 7 Sep 13 at 21:51 UTC in the outer San Luis Bay about 16 km WSW of DCPP. It was about 18 and 22 km away from Temp-2 and Temp-1 respectively. Figure 18 shows the recordings of this event on both portable instruments (bottom six traces) as compared to OBS-4 (top three traces). While both OBS-4 and Temp-2 recorded both P-and S-waves clearly, the record of Temp-1 shows a different picture. There the onsets are masked by strong noise affecting only Temp-1 at this time. The only visible effect of this earthquake on Temp-1 are the Lg-waves arriving between 21:51:09 and 21:51:10 (black circle in figure 18). Under noisy conditions, an EQ with an Ml=1.3 in about 20 km distance seems to be the detection threshold of the portable OBS.
Fig. 18: Recordings of earthquake in Outer San Luis Bay with the three respective components of OBS-4 (top), temp-2 (middle) and Temp-1 (bottom). The 20 sec of data shown here are filtered by a highpass with a corner of 1 Hz.
4.
Conclusions While all compents of both instruments deployed for this project worked flawlessly and there are no data gaps, the data are very often dominated by noise from various sources and varying intensity. Some of the noise originates as natural or manmade acoustic emissions in the ocean, as swell and wave action on the sea surface, or from life on the sea floor. This noise, the absence of direct protection against waves and currents, and the suboptimal coupling of the sensors to the sea floor limit the detection capabilities of the two portable OBS. While the actual lower detection limit still needs to be defined in a more thorough analysis of the data, we find evidence in this initial investigation that such portable OBS in shallow waters are capable of recording events of magnitude just above 1 at a distance of about 25 km.
Version 2.1 2/10/2014 Page 16/17 Page 17 of 18 GEO.DCPP.TR.14.04 R0 Appendix G
Portable OBS Document history:
Version 1.0 20 Dec 13 new document Version 2.0 6 Feb 14 major re-write of chapter 3 Version 2.1 10 Feb 14 edited figure captions, layout Version 2.1 2/10/2014 Page 17/17 Page 18 of 18 GEO.DCPP.TR.14.04 R0 Appendix G