Hyperspectral core logging for fire reconstruction studies
Résumé
Lacustrine sediments contain a wide range
of proxies that enable paleoenvironmental reconstructions.
For instance, charcoal can be used to document
past fire regime changes. In order to analyse hightemporal-
and spatial-resolution records, however, it is
necessary to develop fast, low-cost and high-stratigraphic-
resolution methods. We developed a new
paleo-fire proxy by studying a lacustrine core from the
Esterel Massif, SE France, an area affected by two
recent fire events, in AD 1987 and 2003. For this
purpose, we searched for charcoal deposited and
preserved in the lake sediments by combining a
number of complementary methods, including: classic
macrocharcoal tallying, scanning spectrophotometry,
scanning hyperspectral imaging and high pressure
liquid chromatography analyses. Macrocharcoal
quantification is efficient, but time-consuming, and
only provides intermediate-resolution data (cm scale).
Spectrophotometry, used classically to quantify colour,
is very fast, provides high-resolution data (4 mm)
and is non-destructive (core preservation). Hyperspectral
data have the same advantages as spectrophotometry,
but offer higher spatial resolution (64-lm pixel
size) and higher spectral resolution (6 nm) for core
logging applications. The main result of this research
is based on hyperspectral analysis at very high
stratigraphic resolution using the I-band index. This
index usually measures reflectance values at [660,
670 nm] corresponding to the trough in red reflectance
produced by Chlorophyll a and its diagenetic products.