Backscatter extracted from gridded bathymetry of the banktops and shelf environments of the Tinian, of the Commonwealth of Northern Mariana Islands (CNMI).
This acoustic backscatter imagery was created using data gathered from multibeam soundings for use as a planning and reference document. Refer to supplemental information for description of instrument and survey.
Data were collected aboard the R/V AHI (Acoustic Habitat Investigator),a 25' survey launch owned and operated by the NOAA Pacific Islands Fisheries Science Center in Honolulu, HI. The R/V AHI's survey sensors include a 240 kHz RESON 8101-ER sonar providing bathymetry and imagery data, a TSS/Applanix POS/MV Model 320 which measures position, velocity, attitude and heading, and a Seabird SBE 19 CTD used to measure sound velocity profiles. Equipment serial numbers and software versions are as follows: RESON 8101-ER multibeam echosounder DOC inventory #: CD0000537418 Firmware, dry: 8101-2.07-2D4D Firmware, wet: 8101-1.06-2F6B POS/MV Model 320, version 3 DOC inventory #: CD0000476647 PCS serial #: 474 IMU serial #: 203 Controller software: v 1.0.5.0 Seabird SBE19 CTD: Serial #: 3029 R/V AHI Lever Arm Distances and Alignment Offsets The R/V AHI Reference Point (RP) is defined to be the intersection of the vessel's centerline, the cabin deck and the bulkhead immediately aft of the transducer. This is marked by a punch in the deck weld at that location. Positive X means the point is forward of the RP, positive Y means the point is to starboard of the RP, positive Z means the point is below the RP. The loaded waterline is defined as the intersection of the vessel's performance wing with the hull at the transom. Antenna Baseline Distance, m: 1.229 Transducer depth below waterline, m 0.62 RP to IMU 0.80 0.00 0.08 RP to Primary GPS Antenna -3.55 -0.61 -1.88 RP to Vessel 0.16 0.00 0.77 RP to Sensor 1(MB transducer) 0.16 0.00 0.77 RP to Sensor 2 0 0 0 RP to Aux. GPS Antenna 0 0 0 RP to Heave lever arm(deg) -0.67 0.00 0.00 IMU rotation Ref. Frame, deg 0 0 0 Sensor 1 rotation Ref. Frame, deg 0 0 0 Sensor 2 rotation Ref. Frame, deg 0 0 0 Roll offset: +0.5 deg Pitch offset: 0.0 deg Gyro offset: 0.0 deg
ground condition
These data are not to be used for navigation purposes. Please acknowledge the NOAA Coral Reef Ecosystem Division, Pacific Islands Fisheries Science Center as the source of this information.
NOAA IRC
NMFS/PIFSC/CRED
1845 WASP Blvd., Building 176
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Pacific Islands Benthic Habitat Mapping Center, Coral Reef Ecosystem Division (CRED), Pacific Islands Fisheries Science Center (PIFSC), NOAA
Data are collected for resource management and research purposes and are tested for internal consistency; however, no effort is made to compare these data to external references or to other published data.
Unspecified
Complete
Horizontal positioning system: GPS SPS Horizontal position accuracy: 1.0 meters
Range resolution of sonar: approximately 1.25 cm Raw sounding resolution: 1 cm Vertical accuracy of gridded product: approximately 1 meter
Science Applications International Corporation's (SAIC) ISS-2000 acquires, processes and records data, provides survey control and underway quality control displays. SAIC's SABER processing software is used to process the raw soundings, analyze the results, manually edit the sounding data to remove outliers and derive average gridded data values. The data have been corrected for observed tides from Guam tide gauge 1630000 with a time corrector of 18 minutes and a tide height multiplier of 0.94 using SABER postprocessing software. The data were also recorrected for observed sound velocities in postprocessing. Hawaii Mapping Research Group (HMRG) processing software was then used to extract values of acoustic intensity from the soundings. HMRG is an organization of scientists, engineers and technicians whose mission is to design, build, and operate tools for mapping the seafloor. HMRG is a group within the School of Ocean and Earth Science and Technology at the University of Hawaii at Manoa. The gsf2mr program (July, 2003) converts the swath bathymetry ping records contained within a GSF (Generic Sensor Format) version 2.02 dataset into mr1file format. This is done as follows: (i) position each beam's bottom detect intensity sample at the across-track location of that beam's bathymetry value; (ii) assuming a flat bottom in the near neighborhood of the beam, compute across-track distances for all of the beam's remaining intensity samples based on their temporal relation to the bottom detect sample and the computed average sound velocity for that beam as derived from its range and travel time; (iii) after all of the intensity samples from all beams of a ping have been located in across-track distance, fill the gaps between them as necessary by interpolation. The conversion described above is necessary in order to run HMRG backscatter processing operations on the data, such as filtering to remove noise, and to create netCDF grids, raster images and geotiffs. GMT was then used to reformat the acoustic imagery when necessary. Interactive Visualization System's Fledermaus, ESRI ArcGIS, and RSI ENVI were used for viewing results and creating browse objects. Software used: SAIC ISS-2000 Acquisition Software, v 3.4 (20030610) SAIC SABER Processing Software, v 2.0.2 (20030610) Hawaii Mapping Research Group (HMRG) Processing Software GMT Generic Mapping Tools, v 3.4.2 (20021002)
Sidescan data within a GSF file are arranged as small sequences of intensity values, one sequence per beam per ping. The intensity values represent the amplitude of echo returns to the sensor and can be related to seabed roughness.
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These data are not to be used for navigational purposes. NOAA makes no warranty regarding these data, expressed or implied, nor does the fact of distribution constitute such a warranty. NOAA cannot assume liability for any damages caused by any errors or omissions in these data, nor as a result of the failure of these data to function on a particular system.
