Simultaneous estimation of benthic fractional cover and shallow water bathymetry in coral reef areas from high-resolution satellite images

This article describes the development of a technique to estimate shallow water
benthic cover and depth simultaneously from high-resolution satellite images of
reef areas, specifically from the high-resolution sensor onboard IKONOS. The
technique to derive the estimates of five bottom benthic cover types (sand, coral,
seagrass, macroalgae and pavement) and depth from the four-band images uses
a coupling of radiative transfer (RT) theory and spectral unmixing implemented
in an iterative manner. To resolve the cover types for the unmixing, the method
employed a combinatorial approach to select benthic cover composition. The estimation
technique was applied to two reef areas around the coast of the Ishigaki
in southern Ryukyus, namely, the Fukido River mouth area and the Shiraho Reef.
The IKONOS images of Fukido River mouth area and Shiraho Reef were acquired
in 2003 and 2002, respectively. The accuracy of the fractional cover and the depth
estimates from the satellite images are then presented and compared with sea truth
data and depth measurements. The results indicate good correspondence between
estimated and measured depths, while the estimates for the benthic cover were at
reasonable levels of accuracy.