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Cruise Report; RV Moana Wave cruise M1-01-GM; the bathymetry and acoustic backscatter of the mid shelf to upper slope off Panama City, Florida, northeastern Gulf of Mexico; September 3, through October 12, 2001, Panama City, FL to Panama City, FL

The Maps

Overview and section maps of backscatter and shaded relief (Appendix I) were generated from 45 larger-scale subarea maps (Figure 9, 26kb and Table 6). The 4-m-resolution subarea maps were regridded at 8 m to produce the series of section maps of the entire area (see examples Figure10, 39kb and Figure 11, 38kb). This regridding sacrifices resolution in the shallower areas but allows the entire area to be mapped. The detailed subarea maps are 3750 columns (14 km) by 2500 rows (10 km) in size and were produced at the maximum resolution as determined by water depths and beam angle.

A shaded-relief map (Figure 10 , 39kb and back of report) is a pseudo-sun-illumination of a topographic surface using the Lambertian scattering law (equation 1), where SI is the pseudo-sun intensity, K is a constant that allows for even background, and F is the angle between the pseudo sun and the bathymetric surface.

SI = K * cos F (Eq. 1)

The backscatter map (Figure 11, 38kb and back of report) is a representation of the amount of acoustic energy, at ~95 kHz, that is scattered back to the receiver from the seafloor. The Kongsberg Simrad EM1002 system has been calibrated at the factory and all gains, power levels, etc. that are applied during signal generation and detection are recorded for each beam and are used to adjust the amplitude value prior to recording. Consequently, the backscatter is calibrated to an absolute reflectance of the seabed. However, the amount of energy, measured in decibels (dB), is some complex function of constructional and destructional interference caused by the interaction of an acoustic wave with a volume of sediment or, in the case of hard rock, the rock material. The backscatter from sediment represents volume reverberation to at least 5 cm caused by seabed and subsurface interface roughness above the Rayleigh criteria (a function of acoustic wave length), the composition of the sediment, and its bulk properties (water content, bulk density, etc.). Although, it is not yet possible to determine a unique geological facies from the backscatter value, reasonable predictions can be made from the backscatter based on the known local geology.

Table 6. Map numbers, resolution in meters/pixel and size in pixels

One of the great advantages of this survey is that every sounding of the bathymetry is accurately georeferenced and coregistered with the backscatter. Each pixel on the map has a latitude, longitude, depth, and backscatter value assigned to it. Consequently, there is no ambiguity in correlating the backscatter to the bathymetry, as is often the case when correlating sidescan sonar with bathymetry.

Any use of trade, product, or firm names is for descriptive purposes only and does not imply endorsement by the U.S. Government.

Suggested citation:

Gardner, James V., Mayer, Larry A., Hughes Clarke, John E., Dartnell, Peter, Sulak, Kenneth J., 2001, Cruise Report; RV Moana Wave cruise M1-01-GM; the bathymetry and acoustic backscatter of the mid shelf to upper slope off Panama City, Florida, northeastern Gulf of Mexico; September 3, through October 12, 2001, Panama City, FL to Panama City, FL: U.S. Geological Survey Open-File Report 01-448, https://pubs.usgs.gov/of/2001/0448/.

U.S. Department of the Interior
SALLY JEWELL, Secretary

U.S. Geological Survey
Suzette M. Kimball, Acting Director