MODIS and ASTER synergy for characterizing thermal volcanic activity

Abstract

Volcanic activity is diverse in its manifestations and spans wide temporal and spatial scales. Monitoring volcanoes with any single sensor system can only provide a limited perspective on the nature of such activity because of trade-offs between spatial, temporal and spectral resolution. Spaceborne observations of volcanoes are thus optimized by utilizing data from different and complementary remote sensing instruments. This study examines the combined use of the Moderate Resolution Imaging Spectroradiometer (MODIS) and the Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) for analyzing thermal anomalies from four separate volcanoes: Erta 'Ale (Ethiopia), Kīlauea (Hawai'i), Láscar (Chile) and Kliuchevskoi (Russia). MODIS provides a high temporal resolution (daily) but low spatial resolution (~1km) dataset and is used to measure volcanic thermal radiance. ASTER provides relatively high spatial resolution (~90m) image data and is used to define the size of thermal features, albeit at a poorer temporal frequency. Erta 'Ale and Kīlauea have been erupting continuously over the 11-year study period and their thermal emission signatures reveal a persistent baseline on which occasional increases in thermal output, associated with more profuse effusions of lava, are superimposed. Kliuchevskoi also displays occasional peaks in thermal activity due to the eruption of lava however intervening periods are characterized by weak or absent thermal anomalies. Láscar, on the other hand, provides an example of volcanic activity that is difficult for MODIS-type sensors to detect. It is characterized by fumarolic activity that is too low in temperature and too spatially limited to be readily detectable with its coarser instantaneous field of view (i.e., pixel size). However, high resolution data from ASTER can be used to supplement and complement the MODIS dataset. Beyond characterizing the size of thermal anomalies ASTER can also provide constraints on their shape, location and orientation and is capable of detecting relatively subtle thermal anomalies given its high spatial resolution thermal infrared wavebands. These qualities permitted the identification of a thermal precursor to lava flows at Kliuchevskoi. The precursor, which was associated with a rising lava lake, is characterized as an increase in the size and intensity of ASTER-detected thermal anomalies situated in the active crater. Wavelet analysis of the MODIS dataset was also carried out. This revealed the time scales over which radiant output waxed and waned during individual eruptive episodes as well as the repose time between episodes. Such information might be useful in forecasting the likely duration and onset of future eruptions.