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ON-GOING FOREST FIRE NEAR ANCIENT OLYMPIA, GREECE,
MONITORED WITH IMAGING RADAR FROM SPACE
Background
A wildfire surrounding the area of Ancient Olympia (Figure 1), Western Greece Region, broke
out on August 4, 2021 and is still progressing until this time. Several fronts are still active,
consuming large stretches of pine trees and inhabited areas. Until now, almost 20 square
kilometres have been burnt, while 19 communities have been evacuated for safety reasons.
About 170 firemen, 50 trucks, 6 helicopters and 1 water-bombing aircraft have been recruited
for firefighting purposes. Additional help was provided by volunteer firefighters, water tankers
and machinery that was provided by local authorities.
Residencies have been damaged and firefighters were injured, while the archaeological site
of Ancient Olympia, the birthplace of the Olympic Games, has also been at risk. The high
temperature and strong winds have made it difficult to contain the fire so far. The exact causes
of the fire remain unresolved as of now, however the heat wave of the last week, which has
been characterised as the worst since 1987, has certainly played a significant role in the
ignition.
Figure 1. Location of Ancient Olympia, in Peloponnese, Greece.
Technical Description
Open-access Sentinel-1 C-band data provided by the European Space Agency (ESA) and
Copernicus was used to monitor the extent of these ongoing forest fires in Greece. For
processing the data, the Google Earth Engine (GEE) cloud-based platform was used, where
the original Sentinel-1 data in Ground Range Detected Georeferenced (GRD) format are
already pre-processed to backscatter coefficient σ°. Pre-processing of scenes in GEE was
performed using the SNAP Sentinel-1 Toolbox and included the following steps: applying orbit
file, GRD border noise removal, thermal noise removal, radiometric calibration, terrain
correction (orthorectification) using the SRTM 30-meter Digital Elevation Model (DEM).
Two Sentinel-1 images were used for this preliminary analysis – one image before the fire
event (24 July 2021) and one image during the fire event (05 August 2021). These images
had the same imaging geometry, as both were sensed by the Sentinel-1B satellite at a
descending pass (path number 80) in the Interferometric Wide Swath Mode (IW).
The two images (in both VV and VH polarization) were merged (Figure 2) into a single
multitemporal RGB composite (R: 24/07/21, G: 05/08/21, B: 05/08/21). The map shows such
a visualization of the two VH bands, with a histogram stretching from -25dB to -5dB. The region
that stands out in red corresponds to an area of about 20 square km burned so far
(https://www.google.com/maps/d/edit?mid=180ebi9fZgOsu2xSJut8RbV8LcOYY0UZM&usp=
sharing).
Figure 2. Burned area (in red) during the first two days 4-5/8/21, as monitored by Sentinel-1 data.
Copyright: Contains modified Copernicus Sentinel-1 data processed by Charles University
in Prague (CUNI) and Aristotle University of Thessaloniki (AUTH).
Contacts: Daniel Paluba (CUNI): daniel.paluba@natur.cuni.cz, Antonios Mouratidis (AUTH):
amourati@geo.auth.gr
