Other subprojects have been:
Industrial Plume Detection In Multispectral Remote
Sensing Data
and
Analysis of Casi Data - A Case Study From The Archipelago Of Stockholm
A simple bio-optical model, with parameter values derived from measurements of the inherent optical properties (IOPs) and optically active substances that are known to influence the IOPs, has been developed. A large historical data set of measurements of the concentration of chlorophyll a and phaeophytine a (Chl), suspended inorganic particulate material (SPIM) and the absorption coefficient of colored dissolved organic matter (CDOM), spanning more than 25 years, has been used together with the model to develop algorithms for the retrieval of these water quality parameters, for a site in Lake Mälaren, Sweden. The model takes as input the optically active substances and outputs a reflectance spectrum just above the water surface. From the modelled reflectance, algorithms were derived for Chl, SPIM and CDOM absorption at 420 nm FIG 1. The algorithms were applied to atmospherically corrected remote sensing data, which were collected by the compact airborne spectrographic imager, CASI. The radiative transfer code 6S was used for the atmospheric correction of the data. Distribution maps (see belov) for the three retrieved parameters were constructed and Chl and SPIM were validated by continuous field measurements of fluorescence and beam attenuation. The continuous data were calibrated with water analysis results from 9 water samples. The time lag between the image acquisition and the ground truth measurements was never more than 3 hours. Even though the model parameter values were collected at different times than the CASI over-flight, and from a larger geographic region of Lake Mälaren than that used for the CASI measurements, the independently developed algorithms predicted the concentration s of the optically active substances within a reasonable level of accuracy, allowing spatial variations in the substances to be predicted.
The spectral bands investigated, were the bands used by the CASI instrument during the SALMON project. These bands are similar to those of the Meris sensor, which is one reason why our results are interesting for the community of the researchers dealing with water quality. The use of MERIS for water quality applications, mainly sea water, has been discussed earlier in several papers. Our CASI derived water quality maps have been validated by an extensive ground truth data set, with positive results.
We think that this methodology with analytical modelling and an inversion approach has a great potential. It provides an alternative to the commonly used regression techniques, which tend to generate unnecessarily site and/or sensor specific algorithms. There is of course a risk in our method, to tune the model too well to the studied lake, and thereby get the same kind of site specific algorithms. The model will be used on more remote sensing scenes and on more lakes in the near future, to further investigate its potential. The Figure below shows Chlorophyll a, Total suspended matter and Dissolved substances in Lake Malaren, August 1997.
Other subprojects have been:
Industrial Plume Detection In Multispectral Remote
Sensing Data
and
Analysis of Casi Data - A Case Study From The Archipelago Of Stockholm