More information about the individual USGS surveys conducted as part of the northern Cape Cod Bay project can be found on the Woods Hole Coastal and Marine Science Center Field Activity webpage:
06012: <http://quashnet.er.usgs.gov/data/2006/06012/> 07001: <http://quashnet.er.usgs.gov/data/2007/07001/> 07002: <http://quashnet.er.usgs.gov/data/2007/07002/> 07003: <http://quashnet.er.usgs.gov/data/2007/07003/> 08002: <http://quashnet.er.usgs.gov/data/2008/08002/>
Field activities 07001, 07002, and 08002: The SWATHplus transducers were mounted on a rigid pole from the bow of the R/V Rafael, approximately 0.5 m below the water line during surveys 07001 and 08001, and 2.6 m below the water line on the starboard side for survey 07002. Position data were recorded by Hypack software to Hypack raw files using an Ashtech Z-Surveyor Extreme for real-time kinematic (RTK) navigation, and an Ashtech BR2G for Differential Global Positioning System (DGPS) navigation. DGPS navigation from the primary F180 antenna was recorded to the raw sonar data files (SXR) via SWATHplus acquisition software. A conservative estimate of positional accuracy is +/- 2 meters.
During 06012, a TSS DMS 2-05 motion reference unit was mounted directly above the sonar transducers and continuously recorded and sent vertical displacement (heave) and attitude (pitch and roll) of the vessel during acquisition to the SWATHplus software. During 06012 vessel heading was determined by a KVH compass that was corrected for magnetic variation of +15.583 degrees (from NOAA Chart number13246 36th ed., Mar. 10/01) during post processing. During 07002, a Coda Octopus F180 inertial-motion unit, mounted directly above the transducers, measured true heading, vertical displacement (heave) and attitude (pitch and roll) of the vessel during acquisition.
Field activities 07001 and 08002: the SWATHplus transducers were mounted on a rigid pole on the bow of the R/V Rafael, about 0.5 m below the waterline. A Coda Octopus F180 inertial-motion unit, mounted directly above the transducers, measured true heading, vertical displacement (heave) and attitude (pitch and roll) of the vessel during acquisition.
Navigation: Field activity 06012: Real-Time Kinematic (RTK) GPS navigation was used to determine the horizontal and vertical position (xyz) of the GPS antenna mounted directly above the SWATHplus transducers with sub-meter accuracy. The RTK-corrected coordinates were transmitted to the ship from a land-based RTK-GPS station established by the USGS at NOAA Tidal Station #8446009 in Brant Rock Harbor, MA.
Field activities 07001, 07002, and 08002: Differential GPS (DGPS) navigation was used to determine the horizontal position (x,y) of the GPS antenna mounted directly above and forward (F180R primary antenna, 0.5 meters) of the SWATHplus transducers with +/- 1-2 meter accuracy. RTK-GPS was used to determine the vertical position of the Ashtech GPS antenna (z) with sub-meter accuracy.
Vertical coordinates for all four surveys were referenced to Mean Lower Low Water (MLLW) using the offset between the North American Vertical Datum of 1988 (NAVD 88) and MLLW published for the tidal benchmark. Horizontal (x and y) and vertical (z) offsets between the transducers, motion sensor, and GPS antenna were precisely measured and recorded within the SWATHplus acquisition software (SEA Swath Processor (2005)), which established the motion sensor as the common reference point during data acquisition.
Speed of Sound: Sound-velocity profiles were collected approximately every 2 hours by a hand-casted Applied MicroSystems SV Plus sound velocimeter. The depth of the transducers below the sea surface was measured and recorded within the SWATHplus acquisition software, and used as a reference point for deriving the acoustic ray path based on sound velocity profiles.
Tides: During post-processing, soundings were referenced to local MLLW by using orthometric to chart datum offsets obtained from NOAA Tidal Station #8446009 at Brant Rock Harbor, Massachusetts. Data were processed and gridded by using the SEA SWATHplus Swath Processor (version 10.0) CARIS Hydrographic Information Processing System (HIPS version 6.1).
B. The files extracted from CARIS HIPS have 4-5 navigation fixes per second. Each file was subsampled to 1 fix per second by using AWK (see code below) to remove the fractions-of-a-second from the time column then grabbing the first occurrence of each second. > awk '{print $1" "substr($2,1,8)" "$3" "$4" "$5}' greped_combined.txt | awk '$2 != prev { print; prev = $2 }' > 2.CCB_NAV_awked.txt
C. Checked that there were no additional spurious fixes outside the survey area using another series of AWK code (see code below), and reformatted for conversion from comma separated value (CSV) data to ESRI point feature class > awk -F" " '{if(substr($4,1,3)=="-70") print $0}' 2.* | awk -F" " '{if(substr($3,1,1)=="4") print $0}'| awk -f reformat_CARIS2Arc_CCB.awk > CCB_bathyNAV_all.csv