7th Workshop on Forest Fire Management - EARSeL, European ...

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II - VALIDATION OF RS PRODUCTS FOR FIRE MANAGEMENT
NWP can provide spatially distributed data at a reasonable resolution by
downscaling and interpolating the surface meteorological variables
(Aguado et al., 2007), but they have a limited accuracy due the downscaling
and interpolation tasks, as well as that forecasted data may deviate
from observations due to the stochastic nature of the atmosphere.
Thermal infrared data has been proven to be useful to estimate air temperature
and water vapor pressure (Goward et al., 1994), and thus our hypothesis
is that it is possible to retrieve dead fuel moisture content from remote
sensing data. Goward et al. (1994) proposed an algorithm to estimate air
temperature with AVHRR data. This algorithm (hereafter called TVX) is
based on the observed linear relationship between the Land Surface
Temperature (LST) and a vegetation index (NDVI), as a measure of vegetation
cover. If a linear regression can be obtained between LST and NDVI,
the air temperature can be retrieved by extrapolating this line to a maximum
cover NDVI (NDVI max ) since vegetation canopies barely deviates from
air temperature in a few degrees. For more details about this algorithm the
reader is addressed to Goward et al. (1994). On the other hand, most of the
water vapor is concentrated in the lowest layers of the atmosphere, since
the decrease of water vapor through the atmosphere follows a power law
(Smith, 1966). Although several authors pointed out that the reliability of
estimates with daily data decreases compared to longer periods (Bolsenga,
1965; Schwarz, 1968), total precipitable water (W) has been related to
daily surface humidity with remote sensing data (Goward et al., 1994).
2 - Objective
This study aims to estimate dead fuel moisture content through the
retrieval or air temperature and relative humidity from remote sensing data.
Calibration and validation data has been acquired from a meteorological
station located in the National Park of Cabañeros (39.319758ºN,
4.394824ºW). This station provides hourly data of temperature and relative
humidity. Only data during spring and summer were used for calibration and
validation since it is the most critical season for wildfire assessment.
3 - Methods
3.1 - Satellite processing
Images from Meteosat Second Generation-Spinning Enhanced Visible and
Infrared Imager (MSG-SEVIRI) were selected since it provides an excellent
temporal resolution (15 minutes) at an adequate spatial sampling (3km at
sub-pixel nadir). Bands centered in 10.8µm and 12.0µm for the Iberian
Peninsula have been used together with the EUMETSAT cloud mask to produce
daily estimates of W. We have exploited the air temperature daily cycle