Retrieval of inherent optical properties from Landsat ETM+ data: possibilities and limitations

Many studies have been carried out to retrieve water quality measures like concentrations of suspended matter and chlorophyll from Landsat TM images. Such studies typically use extensive in-situ measurements and empirical data fitting (usually correlations) to retrieve concentrations of the water constituent under investigation. One disadvantage of such empirically derived algorithms is that they tend to be applicable only to the water constituent, the particular location and water type investigated. In addition, the atmospheric effects are either not taken into account or a uniform atmosphere is assumed. On the other hand, the backscattering and absorption coefficients, have been shown to determine the water color and hence, the measured reflectance. We report on our attempt to retrieve these inherent optical properties from Landsat ETM+ data. We show how we can correct for the atmospheric effects using Band 4. Using current ocean color models, we retrieved the backscattering and absorption coefficients from Bands 1, 2 and 3 for the coastal waters around Singapore. The derived backscattering and absorption coefficients are within the range of values retrieved using Hyperion data and those from in-situ measurements. The advantage of this method is that minimal empirical data are needed and so it can be easily applied to other similar data sets. However, the precision of the retrieved coefficients is necessarily coarse.