Zp. Lee et al., Hyperspectral remote sensing for shallow waters: 2. Deriving bottom depthsand water properties by optimization, APPL OPTICS, 38(18), 1999, pp. 3831-3843
In earlier studies of passive remote sensing of shallow-water bathymetry, b
ottom depths were usually derived by empirical regression. This approach pr
ovides rapid data processing, but it requires knowledge of a few true depth
s for the regression parameters to be determined, and it cannot reveal in-w
ater constituents. In this study a newly developed hyperspectral, remote-se
nsing reflectance model for shallow water is applied to data from computer
simulations and field measurements. In the process, a remote-sensing reflec
tance spectrum is modeled by a set of values of absorption, backscattering,
bottom albedo, and bottom depth; then it is compared with the spectrum fro
m measurements. The difference between the two spectral curves is minimized
by adjusting the model Values in a predictor-corrector scheme. No informat
ion in addition to the measured reflectance is required. When the differenc
e reaches a minimum, or the set of variables is optimized, absorption coeff
icients and bottom depths along with other properties are derived simultane
ously For computer-simulated data at a wind speed of 5 m/s the retrieval er
ror was 5.3% for depths ranging from 2.0 to 20.0 m and 7.0% for total absor
ption coefficients at 440 nm ranging from 0.04 to 0.24 m(-1). At a wind spe
ed of 10 m/s the errors were 5.1% for depth and 6.3% for total absorption a
t 440 nm. For field data with depths ranging from 0.8 to 25.0 m the differe
nce was 10.9% (R-2 = 0.96, N = 37) between inversion-derived and field-meas
ured depth values and just 8.1% (N = 33) for depths greater than 2.0 m. The
se results suggest that the model and the method used in this study, which
do not require in situ calibration measurements, perform very well in retri
eving in-water optical properties and bottom depths from above-surface hype
rspectral measurements. (C) 1999 Optical Society of America.