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

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I - PRE-FIRE PLANNING AND MANAGEMENT
2 - Methodology
2.1 - Data collection
Burbage Moor, located south west of Sheffield (United Kingdom) on the
edge of the Peak District National Park, was the test site. It is characterised
by flat topography and composed of homogenous Calluna vulgaris stands of
different ages and conditions, areas of grassland dominated by Eriophorum
angustifolium, bog and areas of Pteridium aquilinum invasion. A field campaign
was carried out in 2008, focusing on 10 plots consisting of Calluna
stands of different ages, Eriophorum angustifolium and mixed Eriophorum
angustifolium and Calluna stands. At each plot canopy height and vegetation
composition were recorded and vegetation samples were collected for
FMC estimation. In addition, the spectral reflectance was measured using a
field spectroradiometer. The spectral measurements of the vegetation and a
series of light and dark calibration targets were acquired from a nadir position
2m above each plot. This field work was concurrent with airborne
hyperspectral data acquisition. Hyperspectral images from the AISA Eagle
and Hawk instruments (390-2450 nm) were collected by the U.K. Natural
Environment Research Council (NERC) Airborne Remote Sensing Facility
(ARSF) over three parallel North/South flight lines on May 6 th and July 1 st
2008.
2.2 - Laboratory work and image processing
The vegetation samples were stored in well-sealed plastic bags to avoid
moisture loss and transferred to the laboratory for gravimetric moisture
analysis on the day of data collection. The fresh weight (Wf) of each sample
was measured using an electronic balance and then they were dried for
48 hours at 60°C, as recommended by Chuvieco et al. (2002), and their dry
weight (Wd) determined (equation1).
FMC= [Wf-Wd/Wd]*100 (1)
The radiance values for the study plots were extracted from the airborne
images of the two dates and corrected to reflectance using the field spectroradiometer
measurements from the calibration targets, using a band-byband
linear regression approach. The first derivative was calculated using a
simple difference function, where a 7nm gap was taken either side of a
given wavelength. Landsat TM-equivalent reflectance was calculated for
each plot and was used to calculate broad band vegetation indices (VI).
Linear correlation coefficients were calculated between FMC and spectral
reflectance, the first derivative and with the VIs for all the plots and for
Calluna plots only.