Vol. 12, No. 1, 44-57, 2013

Abstract
The analysis of littoral bottom properties such as bathymetry and coverage (i.e. plant identification) often requires knowledge about the composition of relevant optically active water constituents like phytoplankton, suspended particulate matter and coloured dissolved organic matter, which influence the radiative transfer in water due to scattering and/or absorption. These inherent optical properties (IOPs) of the water column can be retrieved in optically deep water (i.e., with no reflectance contribution of the bottom) by using physically based inversion techniques. In shallow water - which often differs from deep water in the amount of water constituents due to terrestrial input from the shore - a reliable estimation of IOPs requires at least a valid bottom reflectance, which is difficult to measure in water. An accurate estimation of water constituents is essential to the retrieval of bottom reflectance and subsequent identification of invasive aquatic plants, which was the main goal of this project.

In an experimental approach, the application of artificial surfaces for retrieving water constituents as well as bottom depth was tested during the hyperspectral APEX campaign 2011 covering Lake Starnberg in southern Germany. Two silo foils (10 metres wide and 50 metres long) were spread on the littoral bottom covering depths from 0.5 to 16 metres and acting as a very bright (white side of the foil) as well as a very dark (black side of the foil) reflective bottom albedo for the ENVI add-on BOMBER in terms of water constituents retrieval and bottom depth estimation. Reflectance spectra of the foils are known from laboratory measurements. In situ measurements were performed in water using RAMSES spectrometers and processed using the algorithms implemented in BOMBER as well as the inversion software WASI. The results show best performance for the black sided foil regarding pixel unmixing, water constituent retrieval and depth estimation, which agreed well with the WASI inversion results of the downwelling irradiance, which was used for validation due to lacking bottom influence.

ISSN 1729-3782