Analysing explosive volcanic deposits from satellite-based radar
backscatter, Volcan de Fuego, 2018
Abstract
Satellite radar backscatter has the potential to provide useful
information about the progression of volcanic eruptions when optical,
ground-based, or radar phase-based measurements are limited. However,
backscatter changes are complex and challenging to interpret: explosive
deposits produce different signals depending on pre-existing ground
cover, radar parameters and eruption characteristics. We use high
temporal- and spatial-resolution backscatter imagery to examine the
emplacement and alteration of pyroclastic flows, lahars, and ash from
the June 2018 eruption of Volcan de Fuego, Guatemala, drawing on
observatory reports and rain gauge data to ground truth our
observations. We use dense timeseries of backscatter to reduce noise and
extract deposit areas. Backscatter decreases where six flows were
emplaced on 3 June 2018. In Barranca Las Lajas, we measured a
11.9-km-long flow that altered an area of 6.3 km2; and used radar
shadows to estimate a thickness of 10.5 +/- 2 m in the lower sections.
The 3 June eruption also changed backscatter over an area of 40 km2,
consistent with ashfall. We use transient patterns in backscatter
timeseries to identify nine periods of high lahar activity in B. Las
Lajas between June and October 2018. We find that the characterisation
of subtle backscatter signals associated with explosive eruptions is
assisted by (1) radiometric terrain calibration, (2) speckle correction,
and (3) consideration of pre-existing scattering properties. Our
observations demonstrate that SAR backscatter can capture both the
emplacement and subsequent alteration of a range of explosive products,
allowing the progression of an explosive eruption to be monitored.