GEOMETRIC CONSIDERATIONS FOR THE REMOTE MONITORING OF VOLCANOS - STUDIES OF LAVA DOMES USING ATSR AND THE IMPLICATIONS FOR MODIS

Data from the Moderate Resolution Imaging Spectrometer (MODIS) may be used for the thermal monitoring of volcanoes from the NASA Earth Obser ving System. MODIS uses a wide scan angle to provide a high temporal f requency but this geometry means that zenith angle and pixel size vary greatly across the swath. Similar variations are inherent in radiomet ric data obtained from the forward- and nadir-views of the Along Track Scanning Radiometer (ATSR) and here we use dual-view ATSR data of vol canic lava domes to investigate how these geometric effects influence the retrieved thermal anomalies. The effect of increasing pixel size w ith zenith angle is shown to be counteracted by increasing pixel overl ap, thus providing comparable thermal anomalies from the two ATSR view s in cases where off-nadir obscuration by crater walls is not signific ant. In such instances data from the majority of the MODIS swath could be combined in a single time-series in order to maximise temporal cov erage for volcano monitoring purposes.