Bathymetry and Acoustic Backscatter—Elwha River Delta, Washington

Geodetic Control

Geodetic control for the survey was established using a shore-based Global Positioning System (GPS) base station broadcasting real-time kinematic (RTK) corrections to the survey vessel by UHF radio link. The base station was located at the base of Ediz Hook (fig. 1). The base station was programmed using the WGS84 (G1150) reference frame with an Epoch of 2010.1548. Average National Geodetic Survey Opus Solution coordinates for the station are shown in table 2. Post-processed analysis of the base station coordinates using the precise ephemeris data showed the base station broadcast coordinates were in error by approximately -0.00007" in latitude, +0.00011" in longitude and +0.004m in height. These values are insignificant compared to the positional uncertainty of the vessel and sonar system and were neglected (see Data Processing for details).

Table 2. GPS base station coordinates (Opus solution, see text) used for the SWATH bathymetry survey at Elwha River Delta (Port Angeles, Wash.), February-March 2010.
Name	Value
Reference Frame:	WGS84 (G1150)
Epoch:	2010.1548
Latitude:	N 48° 08' 06.01943"
Longitude:	W 123° 28' 06.90674"
Ellipsoid Height:	-11.355 m
The differences to be added to the broadcast locations are
Latitude:	-0.00007"
Longitude:	+0.00011"
Ellipsoid Height:	+0.004 m
Using UTM coordinates as a comparison the base station was programmed using the following coordinates:
Reference Frame:	NAD83, UTM zone 10
Epoch:	2002.0000
Northing:	5331411.376 m
Easting:	465138.251 m
Ellipsoid Height:	-11.042 m
Orthometric Height:	9.155 m (based Geoid09)

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