Hyperspectral remote sensing of Western Australian coastal waters

Abstract

Hyperspectral remote sensing provides a particularly useful means of determining inherent optical properties of coastal waters where constituents other than phytoplankton add to the optical complexity of the water column. The substantial number of channels, about 200 for most hyperspectral sensors, enables many of the constituents within the water column to be identified spectrally. Additionally, in shallow water the water leaving radiance may include a signal reflected from the sea bottom. A hyperspectral radiometer was deployed on monthly oceanographic cruises off the coast near Perth, Western Australia, to make observations. Field measured reflectance spectra were used as input into a slightly modified version of a reflectance model developed by Lee et al , 1999. Products, including the concentrations of chlorophyll-a (Chl-a ), coloured dissolved organic matter (CDOM), and suspended sediments (SS), as well as the water column depth (H), were extracted from the reflectance model by incorporating an optimisation technique. A Levenberg-Marquardt retrieval scheme was utilised in the optimisation. This scheme involved minimizing the difference between the modelled and measured spectral reflectance curves. Water samples were also collected on the monthly oceanographic cruises and used to determine the concentrations of chlorophyll-a , CDOM and SS. Water depth was measured using the boat's echo sounder. The model-derived products were compared to in situ measurements. The mean difference between model retrieved depth and in situ depth was 12.5 % or 1.4 m (R 2 = 0.98, N =11). Excluding two field measurements taken in the Marmion Marine Park, the mean RMS difference in depth was 7.6 % or 0.9 m (R 2 = 0.99, N =9). The mean RMS difference between retrieved Chl-a concentration and in situ measured Chl-a was 11.1 % or 0.044 mgm-3 (R 2 = 0.91, N =8). These preliminary results suggest that the reflectance model works well for depth and Chl-a retrieval for Western Australian coastal waters and their sandy substrate.© (2003) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.