Synergistic use of satellite thermal detection and science: a decadal perspective using ASTER

Many volcanoes around the world are poorly monitored and new eruptions increase the need for rapid ground-based monitoring, which is not always available in a timely manner. Initial observations therefore are commonly provided by orbital remote sensing instruments at different temporal, spatial and wavelength scales. Even at well-monitored volcanoes, satellite data still play an important role. The ASTER (Advanced Spaceborne Thermal Emission Radiometer) orbital sensor provides moderately high spatial resolution images in multiple wavelength regions; however, because ASTER is a scheduled instrument, the data are not acquired over specific targets every orbit. Therefore, in an attempt to improve the temporal frequency of ASTER specifically for volcano observations and to have the images integrate synergistically with high temporal resolution data, the Urgent Request Protocol (URP) system was developed in 2004. Now integrated with both the AVHRR (Advanced Very High Resolution Radiometer) and MODIS (Moderate Resolution Imaging Spectroradiometer) hotspot monitoring programmes, the URP acquires an average of 24 volcanic datasets every month and planned improvements will allow this number to increase in the future. New URP data are sent directly to investigators responding to the ongoing eruption, and the large archive is also being used for retrospective science and operational studies for future instruments. The URP Program has been very successful over the past decade and will continue until at least 2017 or as long as the ASTER sensor is operational. Several volcanic science examples are given here that highlight the various stages of the URP development. However, not all are strictly focused on effusive eruptions. Rather, these examples were chosen to demonstrate the wide range of applications, as well as the general usefulness of the higher resolution, multispectral data of ASTER. Monitoring of effusive volcanic processes from orbit using thermal infrared (TIR) data has been ongoing from the earliest days of the satellite era (Gawarecki et al. 1965; Friedman & Williams 1970; Scorer 1986). Ramsey & Harris (2013) more recently summarized the history of satellite-based thermal infrared (TIR) research of active volcanoes into four chronological themes based on technology development: (1) hotspot detection; (2) analysis of subpixel components; (3) heat/mass flux studies; and (4) eruption chronologies. These themes follow a predicable pathway based on the available technology and computer processing capabilities at the time of each study. As satellite TIR sensors continue to improve in spatial, temporal and/or spectral resolution, so does the paradigm of spaceborne volcanology. The ability of scientists to extract new informational types from precursory activity through to detailed analysis of the erupted products continues to grow exponentially. The simple detection of a new ‘thermal anomaly’ at a quiescent volcano marking the start of new activity gave rise to detailed analysis of the temperature distribution below the pixel scale, which then allowed more accurate modelling of flux rates and chronological descriptions of each eruptive phase. During the past 50 years of satellite TIR data, a fundamental technological divide has separated these studies: the use of high temporal–low spatial resolution v. low temporal–high spatial resolution data. The former typically falls under a class of sensors designed primarily for weather and atmospheric studies, and includes the Advanced Very High Resolution Radiometer (AVHRR), the Geostationary Operational Environmental Satellite (GOES), the Along Track Scanning Radiometer (ATSR) and the Moderate Resolution Imaging Spectroradiometer (MODIS) instruments. These sensors commonly are designed with wide swath widths, a limited number of spectral bands and spatial resolutions of 1.0 km/pixel or larger, which results in temporal frequencies of minutes to hours. Although this class of sensor has existed since the earliest days of orbital measurements, there were few studies of active volcanic processes using these data because of the poor spatial resolution, low signal to noise (SNR) and the large amount of thermal activity required for detection by these early sensors (Williams & Friedman 1970; Scorer 1985). However, improved analysis techniques that have been designed to extract information below the scale of a pixel have now made these datasets invaluable for both rapid detection of new activity and analysis of timescale-dependent eruptive processes (e.g. Harris et al. 1997b; Wright et al. 2002a; Hirn et al. 2008). The other class of sensors From: Harris, A. J. L., De Groeve, T., Garel, F. & Carn, S. A. (eds) Detecting, Modelling and Responding to Effusive Eruptions. Geological Society, London, Special Publications, 426, http://doi.org/10.1144/SP426.23 # 2015 The Author(s). Published by The Geological Society of London. All rights reserved. For permissions: http://www.geolsoc.org.uk/permissions. Publishing disclaimer: www.geolsoc.org.uk/pub_ethics by guest on December 17, 2015 http://sp.lyellcollection.org/ Downloaded from