GLORIA and Sea Beam data are processed together with a number
of benefits. The Sea Beam data allow an improved slant- to ground-
range projection of the imagery that results in less of the distortions,
such as layover and foreshortening, that are produced when the
seafloor is assumed to be flat. A calculation originally intended to
quantify side scan sonar data has also been found to improve the
images in an image enhancement sense. This calculation involves
estimating the seafloor's backscatter strength from GLORIA side scan
sonar data using a simple physical model and the characteristics of the
GLORIA instrument. The backscatter strength is the ratio of
backscattered to incident sonar intensity on the sea bottom, normalized
to the surface area covered by the acoustic pulse. It is computed by
correcting the GLORIA data for propagation losses, beam directivity
pattern, time-varied amplifier gain and other factors. The calculation
is improved by accounting for refraction in the water column and for
some topographic effects using Sea Beam data. A GLORIA image
from a mid-ocean ridge crest is shown to have a large 60 dB range that
is due to the effect of the system response, such as the beam pattern,
on the images. The corresponding image of the seafloor backscatter
strength has an almost Gaussian distribution of picture element DN
with a narrow range, 20 dB, showing that most of the system effects
have been removed. Cross sections through the backscatter strength
image show flat trends superimposed with finer variations due to the
seafloor geology. The conversion of GLORIA data into seafloor
backscatter strength serves two purposes; it provides quantitative
information that can be used to determine the likely causes of
particular features in the images and it performs what is effectively a
deterministic "shading correction."
Mitchell, N. C., "Improving GLORIA images using Sea Beam data", J. Geophys.
Res. 96, 337-351, 1991.