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 
1014