Preliminary hard and soft seafloor substrate map classified from sidescan data and bathymetric derivatives at Apra Harbor, Guam U.S. Territory. The dataset was created using Bathymetric Position Index (bpi) zones derived from Reson SeaBat 8125 multibeam data at a 1 m grid cell size, and Klein 3000 sidescan sonar data. The sonar frequency is 455 kHz for the Reson Seabat 8125 multibeam echosounder. Additional information on multibeam and sidescan datasets can be found in the Data Acquisition and Processing Report (DAPR) that can be accessed at: www.soest.hawaii.edu/pibhmc. Classification of the bathymetry and sidescan data into hard and soft seafloor substrates were validated using groundtruth data collected for the US Navy in Appendix J of the Final EIS Statement: Guam and CNMI Military Relocation accessed at: http://www.guambuildupeis.us/final_documents. Survey site images can be found at http://guamreeflife.com/htm/reeftour/cvn_survey_sites.htm. Although hard and soft classes from the substrate map are highly correlated with those from the optical validation data, the substrate map should be used with caution as groundtruth data were mostly collected at areas of known hard bottom in less than 60 ft of water depth.
The hard and soft seafloor map is being used to improve sampling techniques for long-term ecosystem monitoring, to guide future ground-truthing operations and to identify coral-rich and species specific environments. This is a preliminary product and the methods used to generate the map are currently being evaluated for their accuracy.
Survey data were acquired by the United States Navy (USN) Fleet Survey Team (FST) with Survey Vessel Swamp Fox. A Reson 8125 multibeam echosounder was mounted from an arm on the port side of the vessel. The Klein 3000 Side Scan Sonar was operated in the stern-towed configuration. Additional detailed information on data acquisition, equipment configuration, and corrections can be found in the Data Acquisition and Processing Report (DAPR), SWAMPFOX_DAPR_2008.pdf, that can be accessed at: www.soest.hawaii.edu/pibhmc and is included in the ZIP file containing the bathymetry grids. See the process description portion of this document for additional information about how the classes were derived.
ground condition
These data are not to be used for navigation purposes. Please acknowledge the NOAA Pacific Islands Fisheries Science Center (PIFSC) Coral Reef Ecosystem Division (CRED) and the Pacific Islands Benthic Habitat Mapping Center (PIBHMC), and the Joint Institute for Marine and Atmospheric Research (JIMAR) and School of Ocean and Earth Science and Technology (SOEST), University of Hawaii as the sources of this information.
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https://www.soest.hawaii.edu/pibhmc/CNMI_images/apra_5m_hardsoft_445.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: see DAPR Horizontal position accuracy: see DAPR
see DAPR Raw sounding resolution: Variable
Processing steps used to generate the sidescan and bathymetry are described in their own metadata that can be found at www.soest.hawaii.edu/pibhmc. Initial efforts to create a hard and soft substrate map using traditional methods at PIBHMC were unsuccessful due to shadowing effects in the sidescan imagery. Instead, Bathymetric Position Index Zones were derived from the gridded multibeam bathymetry (apra_bty_1m) using the Benthic Terrain Modeler (BTM). The BTM (written for ArcGIS 8.x or 9.x) may be downloaded from http://dusk2.geo.orst.edu/djl/samoa/tools.html. BPI Zones are derived from a focal mean analysis on bathymetry and slope wherein bathymetric highs and lows are designated as crests and depressions respectively. After testing 5 experimental scales, the bpi with scalefactor 10 was chosen based on the diameter of reef structures seen in the bathymetry (also after Lundblad et al. 2006; see Supplemental_Information). Two ranges of slope defined flats and slopes: x < 5 and 5 < x < 70. The BPI Zones map was reclassified using the Spatial Analyst>Reclassify tool in ArcMap version 9.3.1 wherein classes equal to crests and slopes were considered hard and classes equal to flats were considered soft. These features were selected to correspond to hard features following visual assessment of the BPI map against the sidescan data. Depressions were validated by the sidescan imagery and called hard when corresponding to a sidescan value < 90 and soft when corresponding to a sidescan value > 90. Some additional areas corresponding to hard sidescan values (< 90) which did not correspond to features identified in the BPI map were also classified as hard. These were manually delineated in the raster using tools in ArcGIS version 9.3.1.
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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.
Arc ASCII can be converted to Arc Raster using ArcToolbox Conversion Tools (ASCIItoRaster).
