11 December 1992
Push-Broom
ISM spectrometer
Landsat TM
SPOT
6 sites: 2, 4, 5, 9
19 April 1993
ISM spectrometer
Landsat TM
on 18 April
4 sites: 4, 6, 9, 10
Table 1: List of available sensors and number of ground sites for each experiment. The site numbers refer
to Table 2. The Push-Broom radiometer and the ISM spectrometer are described in the text.
The studied area is located in a highly mountaneous terrain in the French Alps. A total of 13 sites were
selected for ground measurements: they are all in the Grenoble area for logistic reasons, they are spread
over a large range of elevations (from 1850 m to 3320 m) and slope directions (Table 2). Therefore
different types of snow could be found. Each site was chosen on an homogeneous terrain of at least 100
m x 100 m because of the size of the Landsat TM pixels. They were all directly illuminated by the sun
during the experiments.
Site name
Elev.
(m)
Slope
Site name
11
Slope
1
Val morel
1850
N
2
Auris (2 sites)
1875
SE
7
Lac de la Fare
2640
Hor.
3
Col du Lautaret
2050
S
8
Clot de la Cala
2680
N
4
Alpette
2108
W
9
Col du Lac Blanc
2722
W
5
Col Sabot ( 2 sites)
2200
S
10
Glacier de la Girose
3250
N
6
Glacier de Sarenne
2310
S
11
Pic Bayle
3320
SE
Table 2: Elevation and mean slope direction of the ground measurement sites.
2.1.2. Ground measurements
For each site, at the time of remote sensing data acquisition, were measured the temperature, the snow
density and its liquid water content when necessary. A careful stratigraphy of the upper 30 cm of snow was
conducted. The type and the size of grains were evaluated in situ. Snow samples were collected on the field
and maintained in isooctane below 0°C to prevent them from metamorphism (Brun and Pahaut, 1991 ). Then
they were analysed in a cold room at Grenoble. Moreover large amount of surface snow (0.25 m ) were
taken for reflectance measurements in a cold laboratory. Snow samples were also collected for carbon soot
content. The carbon soot content is measured at the Centre des Faibles Radioactivités de Gif/Yvette, France,
by the Coulometric titration technique. Each site was precisely located on a map and the main features of
the topography ( slope angle and direction) were recorded.
2.2. Remote sensing data
2.2.1. Spaceborne data
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