Abstract
The All-Weather Volcano Topography Imaging Sensor remote sensing instrument is a custom-built millimeter-wave (MMW) sensor that has been developed as a practical field tool for remote sensing of volcanic terrain at active lava domes. The portable instrument combines active and passive MMW measurements to record topographic and thermal data in almost all weather conditions from ground-based survey points. We describe how the instrument is deployed in the field, the quality of the primary ranging and radiometric measurements, and the postprocessing techniques used to derive the geophysical products of the target terrain, surface temperature, and reflectivity. By comparison of changing topography, we estimate the volume change and the lava extrusion rate. Validation of the MMW radiometry is also presented by quantitative comparison with coincident infrared thermal imagery.
Highlights
DIRECT observations of active volcanoes are often severely restricted by environmental conditions, cloud cover, and visible observations of volcanic activity at the summit of a volcano may be impossible or very sparse for days to weeks
The head is attached and the whole instrument manually rotated on the tripod to point at a reference corner cube (CC) reflector deployed in the field at a position measured by differential GPS at ranges of up to ~2 km from the radar
It is possible that the absolute registration of the digital elevation maps (DEMs) for each occupation differs slightly introducing an additional error. Despite these issues, following the analysis described for the first example, the volume change for the differing viewpoints was calculated as 2.54 ± 0.92 106 m3 with a corresponding apparent extrusion rate of 4.75 ± 1.72 m3·s-1
Summary
DIRECT observations of active volcanoes are often severely restricted by environmental conditions, cloud cover, and visible observations of volcanic activity at the summit of a volcano may be impossible or very sparse for days to weeks. The hazard posed by the volcano increases under certain conditions, for example when lava intrudes within the dome rather than reaches the surface [4], and knowledge of changing terrain shape is potentially of great value in forecasting future hazardous behavior This should be detectable by topographic surveys but, given their infrequency, is not generally feasible or reliably done by traditional techniques. Remote sensing techniques that can record topography during periods of poor visibility include satellite and airborne interferometric synthetic aperture radar (InSAR) [5] which can produce digital elevation maps (DEMs) with a few meters height resolution, extensive coverage and sensitivity to small changes in topography They require coherence between repeat passes (typically days/months) which is lost on the rapidly evolving topography of active lava domes rendering the technique useless for monitoring the regions of greatest interest [6].
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