10CCT03_ss_1m.tif: the 1-m resolution grid of the side scan sonar data from USGS Cruise 10cct03
In April of 2010, the U.S. Geological Survey (USGS) conducted a geophysical survey from the east end of West Ship Island, MSiss., extending to the middle of Dauphin Island, Ala. This survey had a dual purpose: (1) to interlink previously conducted nearshore geophysical surveys (shoreline to ~2 kilometers, km) with those of offshore surveys (~2 km to ~9 km) in the ares and (2) to extend the geophysical survey to include a portion of the Dauphin Island nearshore zone. The efforts were part of the USGS Gulf of Mexico Science Coordination partnership with the U.S. Army Corps of Engineers (USACE) to assist the Mississippi Coastal Improvements Program (MsCIP) and the Northern Gulf of Mexico (NGOM) Ecosystem Change and Hazards Susceptibility Project by mapping the shallow geological stratigraphic framework of the Mississippi Barrier Island Complex.
These geophysical surveys will provide the data necessary for scientists to define, interpret, and provide baseline bathymetry and seafloor habitat for this area and to aid scientists in predicting future geomorpholocial changes of the islands with respect to climate change, storm impact, and sea-level rise. Furthermore, these data will provide information for barrier island restoration, particularly in Camille Cut, and provide protection for the historical Fort Massachusetts. For more information refer to <http://ngom.usgs.gov/gomsc/mscip/index.html>.
U.S. Geological Survey - St. Petersburg Coastal and Marine Science Center, DeWitt, Nancy T., Flocks, James G., Pfeiffer, William R., Gibson, James N., and Wiese, Dana S., 20111001, 10CCT03_ss_1m.tif: the 1-m resolution grid of the side scan sonar data from USGS Cruise 10cct03: USGS Data Series Publication DS671, U.S. Geological Survey - St. Petersburg Coastal and Marine Science Center, St. Petersburg, FL.
Planar coordinates are encoded using row and column
Abscissae (x-coordinates) are specified to the nearest 1
Ordinates (y-coordinates) are specified to the nearest 1
Planar coordinates are specified in meters
The horizontal datum used is D_WGS_1984.
The ellipsoid used is WGS_1984.
The semi-major axis of the ellipsoid used is 6378137.000000.
The flattening of the ellipsoid used is 1/298.25722356300003.
Depth_Datum_Name:Mean lower low water Depth_Resolution:1 Depth_Distance_Units:meters Depth_Encoding_Method:Explicit depth coordinate included with horizontal coordinates
This report serves as an archive of the processed multibeam bathymetry and side scan sonar (SSS) data. Data products herein include gridded and interpolated digital depth surfaces, seabed surface backscatter imagery, and x,y,z data products for both multibeam bathymetry and side scan sonar imagery. Additional files include trackline maps, navigation files, Geograpahic Infromation System (GIS) files, Field Activity Collection System (FACS) logs, and formal Federal Geographic Data Committee (FGDC) metadata. Scanned images of the handwritten FACS logs and digital FACS logs are also provided as PDF files. Refer to the Acronyms page for expansion of acronyms and abbreviations used in this report or hold the cursor over an acronym for a pop-up explanation.
The XTF files collected were converted into CARIS HIPS and SIPS version 7.0 data format structure called Sonar Information Processing System (SIPS) for the purpose of editing and side scan mosaic creation. All horizontal positions were offset relative to a central ship navigation point. The first step in SSS data processing was to correct the altitude, or first return. This was achieved by a combination of auto-prediction parameters set and manual boundary digitization of the water column and seafloor. The second step was application of the beam pattern correction, which was accomplished by sampling a series of beams over homogeneous surface content. The purpose of beam pattern correction is to identify and offset the inherent instrument intensity variance as the across-track range increases. Near nadir the acoustic return is significantly more intense and decreases as across-track range increases. These phenomena result in a false high intensity value strip along the centerline of the SSS swath. Several other SSS editing tools were used, including angle-varying gain and time-varied gain corrections, which were used to further smooth the resulting intensity range artifacts, offering a more consistent along- and across-track image. The despeckle editing tool was also employed to identify and mute isolated pixels having extreme high or low intensity values relative to adjacent pixels. After all the individual side scan lines were examined and edited, Geo-referenced Backscatter Rasters (GeoBars) were created. For this dataset a resolution of 1 m was chosen. From the series of GeoBars, a side scan mosaic image was generated as a composite of the GeoBars, which also provides for a continuous image of a single intensity value range for geographic comparison.
Person who carried out this activity:
William R. Pfeiffer
Jacobs Technology Inc., Tampa, FL
600 4th Street South
St. Petersburg, FL
(727) 803-8747 x3134 (voice)
Date: 14-Feb-2017 (process 2 of 2)
Keywords section of metadata optimized for discovery in USGS Coastal and Marine Geology Data Catalog.
Person who carried out this activity:
How well have the observations been checked?
The accuracy of the data is determined during data collection. This dataset is from a single cruise and therefore internally consistent. Methods are employed to maintain data collection consistency aboard various platforms. During mobilization, each piece of equipment (swath and sonar) is isolated to obtain internal and external offset measurements with respect to the survey platform. All the critical measurements are recorded manually and digitally and entered into their respective programs for calibration. Once calibration is complete and calibration status is considered acceptable, then survey operations commence. HYPACK, Inc., HYPSWEEP version 10 was used for the multibeam data acquisition, system calibration,and data post-processing. A patch test was performed at the beginning of the survey to calibrate the SEABAT 8125 and included latency, roll, pitch, and yaw. This involved collecting multibeam data along lines over a sloping surface for the latency, pitch, and yaw tests and over a flat surface for the roll test. The resulting offsets from the patch test were applied to the hardware configuration file prior to survey data acquisition. The Applanix POS MV is not a gyro and therefore did not need calibration. The RESON SeaBat 8125 multibeam transducer head was mounted on a retractable strut-arm that is lowered between the catamaran hulls. Offsets between the sonar head and the DGPS antennas were measured and entered into the respective program. DGPS is always implemented for navigational accuracy. During data acquisition, the differentially corrected positions supplied through the Trimble DSM 212 interface were recorded in the WGS84 datum. Ship heading and motion (roll, pitch, heave) were measured by the Applanix POS MV motion unit. Sound velocity was recorded at the multibeam sonar head. Additional sound velocity casts were conducted at the start and finish of each survey day and as needed throughout the survey. All multibeam bathymetry data were collected using the RESON SeaBat 8125. All side scan sonar data were collected using the Klein 3900 system.
How accurate are the geographic locations?
Differential navigation was acquired using a local National Geodetic Survey (NGS) Continuously Operating Reference Station (CORS) beacon that broadcasts carrier phase and code range measurements that are captured in real-time using the Applanix Position and Orientation System for Marine Navigation (POS MV). The multibeam bathymetry and side scan sonar data were collected simultaneously using HYSWEEP version 10 and SonarPro version 11.3, respectively. The multibeam bathymetry and the side scan sonar data were collected with separate instruments but utilized the same navigation string from the Applanix POS MV. Unless noted, all DGPS data are referenced to WGS84.
How accurate are the heights or depths?
The towfish altitude varied considerably during the cruises due to the nature of shallow-water surveying operations. Ideally, SSS is flown at a relatively considerable distance from the vessel and other instruments to avoid acoustical interference. Typical sources of acoustical interference are vessel vibrations and other instruments that utilize similar frequency ranges. However, in shallow-water surveying the optimal distance is difficult to achieve due to the negative buoyancy of the towfish and the effect of unanticipated isolated shoals.
Where are the gaps in the data? What is missing?
This is a complete processed side scan socar mosaic in GeoTIFF format. These data provide a continuous and complete surface; however, there may in some cases be data missing and inconsistent with reported tracklines. This is directly due to the exclusion of poor data or instrument failures.
This DVD publication was prepared by an agency of the United States Government. Although these data have been processed successfully on a computer system at the U.S. Geological Survey, no warranty expressed or implied is made regarding the display or utility of the data on any other system, nor shall the act of distribution imply any such warranty. The U.S. Geological Survey shall not be held liable for improper or incorrect use of the data described and (or) contained herein. Reference herein to any specific commercial product, process, or service by trade name, trademark, manufacturer, or otherwise does not constitute or imply its endorsement, recommendation, or favoring by the United States Government or any agency thereof.