Multibeam backscatter imagery extracted from gridded bathymetry of Tutuila, American Samoa, South Pacific These data provide coverage between 20 and 5000 meters. The backscatter dataset includes data collected using Simrad EM3002d and Reson 8101 multibeam sonars. The sonars frequencies are 300 kHz and 240 kHz respectively and the backscatter data from each sonar are processed and gridded separately. These metadata are for the 1 m grid cell size Reson 8101 multibeam backscatter data only.
The netCDF grids of backscatter imagery were created using data gathered from multibeam soundings for use as a planning and reference document. The data are also being used for benthic habitat mapping, for locating Essential Fish Habitat, and for studying geologic features of the area. Refer to supplemental information for description of instrument and survey.
Multibeam 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 multibeam bathymetry and backscatter 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. Specific equipment configurations are documented in metadata from cruises: AHI0402 and AHI0602. These metadata can be accessd at: http://www.soest.hawaii.edu/pibhmc/cms/cruise-catalog/. Row Count is 7668 for portrait charts, 6520 for landscape. Column Count is 6520 for portrait charts, 7668 for landscape.
ground condition
These data are not to be used for navigation purposes. Please acknowledge NOAA and the Joint Institute for Marine and Atmospheric Research (JIMAR) University of Hawaii as the sources of this information.
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NMFS/PIFSC/CRED
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http://www.soest.hawaii.edu/pibhmc/amsamoa_images/tutuila-bs_440.jpg
http://www.soest.hawaii.edu/pibhmc/amsamoa_images/tutuila-8101-bs-boxes_440.jpg
PIBHMC, CRED, PIFSC, NOAA and JIMAR
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.
These data are believed to be logically consistent though no tests were performed
Complete
Horizontal positioning system: GPS (SPS) Horizontal position accuracy: 25 meters
1 m Range resolution of sonar ~1.25 cm Raw sounding resolution: Variable Vertical accuracy of gridded product: 1% of water depth
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. Additional data acquisition and processing information can be found in the metadata for cruises AHI0402 and AHI0602. 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 gsf2bs program (July, 2005) converts the swath bathymetry ping records contained within a GSF (Generic Sensor Format) version 2.02 dataset into bs file 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 comparing travel times of beams adjacent to the gap, assigning the position using the adjacent sample closest to nadir, and averaging the interpolated values that fall within a cell. 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 GeoTIFF's. In addition to the standard processing routines applied to Reson 8101 backscatter data, a gain correction was applied to 2006 data to address the larger range of intensity values recorded in 2004 compared to 2006. A scaling value for the 2006 data was empirically derived and applied to all the 2006 data. For more information on the backscatter processing technique see <http://www.soest.hawaii.edu/pibhmc/pibhmc_documentation.htm>. Software_Used: SAIC ISS-2000 Acquisition Software, v 3.4 SAIC SABER Processing Software, v 3.3.15 Hawaii Mapping Research Group (HMRG) Processing Software GMT Generic Mapping Tools, v 4.1 MB System, v 5.0.7
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.
Binary netCDF Grid: This file is formatted as a 2-D binary netCDF grid file. This is the default grid file format used by GMT (Generic Mapping Tools). The file was created by the HMRG sofware program bsovl. More information about netCDF files can be found at at http://www.soest.hawaii.edu/gmt/ and http://www.unidata.ucar.edu/software/netcdf/. List of Tutuila 8101 backscatter netCDF files and bounding coordinates: tutuila-8101-8-01.01.00m.ss.grd W/E/S/N -170.917/-170.473/-14.3833/-14.2076 tutuila-8101-8-02.01.00m.ss.grd W/E/S/N -170.817/-170.473/-14.3167/-14.191 tutuila-8101-8-03.01.00m.ss.grd W/E/S/N -170.917/-170.473/-14.3165/-14.1909 tutuila-8101-8-04.01.00m.ss.grd W/E/S/N -170.883/-170.533/-14.3916/-14.191 tutuila-8101-8-05.01.00m.ss.grd W/E/S/N -170.917/-170.562/-14.3833/-14.1993 tutuila-8101-8-06.01.00m.ss.grd W/E/S/N -170.883/-170.496/-14.3223/-14.1909 tutuila-8101-8-07.01.00m.ss.grd W/E/S/N -170.817/-170.473/-14.3499/-14.1909 tutuila-8101-8-08.01.00m.ss.grd W/E/S/N -170.817/-170.523/-14.3167/-14.2076 tutuila-8101-8-09.01.00m.ss.grd W/E/S/N -170.856/-170.496/-14.3833/-14.1909 tutuila-8101-8-10.01.00m.ss.grd W/E/S/N -170.917/-170.562/-14.375/-14.191 tutuila-8101-8-11.01.00m.ss.grd W/E/S/N -170.746/-170.523/-14.35/-14.2472 tutuila-8101-8-12.01.00m.ss.grd W/E/S/N -170.833/-170.473/-14.3916/-14.2472 tutuila-8101-8-13.01.00m.ss.grd W/E/S/N -170.883/-170.473/-14.3917/-14.1994 tutuila-8101-8-14.01.00m.ss.grd W/E/S/N -170.917/-170.473/-14.3917/-14.1909 tutuila-8101-8-15.01.00m.ss.grd W/E/S/N -170.917/-170.523/-14.3833/-14.2472
