Full text: Mesures physiques et signatures en télédétection

As stated in Table 1 a Landsat TM (Thematic Mapper) was acquired on 24 April 1992. A quarter scene 
is sufficient to cover all the ground sites. On 11 December 1992 we had the chance to get on the same 
day a Landsat TM image at 10:45 a.m. local time and a multispectral SPOT XS image at 11:30 a.m. In 
April 1993 a Landsat image is available which were acquired the day before the experiment. The main 
characteristics of the sensors are given in Table 2. 
2.2.2. Airborne data 
The sensors were installed aboard the French Fokker 27 Avion de Recherche Atmosphérique et de 
Télédétection (ARAT). The altitude of flight was about 5500 m. A GPS and an inertial system were 
available onboard to get the position and attitude of the aircraft. 
The Push-Broom is a radiometer with 3 different channels (Table 3). The acquisition system is constituded 
by an array of 2000 detectors. In December 1992, each site was imaged 2 or 3 times. Some cirrus were 
present at the beginning of the experiment but we still have at least one clear image for each site. 
The ISM is a near infrared spectrometer covering the spectral range from 0.76 pm to 3.16 pm (Table 
3). Each pixel corresponds to a spectrum acquired by two groups of cooled PbS detectors, the spectral 
dispersion being obtained by using a grating whose first two orders are exploited. It is a scanning system 
but non-imaging, i.e. pixels are located on a winding track under the aircraft. Because of the limited 
swathwidth of the sensor, 5 or 6 overflights of the sites were done in December 1992 and 2 overflights in 
April 1993. Many measurements of the incident flux were done from the top of the aircraft with an 
integrating hemisphere and an optical fiber connected to the spectrometer. A video camera was installed 
with ISM to help determining the pixel location. 
Spectral bands 
Pixel size 
Swath width 
Landsat TM 
TM1: 0.45 - 0.52 pm 
30 m x 30m 
180 km 
TM2: 0.52 - 0.60 pm 
30 m x 30m 
TM3: 0.63 - 0.69 pm 
30 m x 30m 
TM4: 0.76 - 0.90 pm 
30 m x 30m 
TM5: 1.55 - 1.75 pm 
30 m x 30m 
TM6: 10.4 - 12.5 pm 
120 m x 120 m 
TM7: 2.08 - 2.35 pm 
30 m x 30m 
Cl: 0.50-0.59 pm 
20 m x 20 m 
60 km 
C2: 0.61 -0.68 pm 
C3: 0.79 - 0.89 pm 
Cl: 0.51 -0.60 pm 
2 m x 2 m 
4 km 
C2: 0.61 - 0.72 pm 
C3: 0.76 - 0.95 pm 
ISM spectrometer 
128 bands between 
0.76 pm and 3.16 pm 
12 m x 12 m 
70 m 
Table 3: Main characteristics of the sensors which were used for the experiments. The pixel size and the 
swath width are given for a mean terrain elevation. 
3.1. Snow samples analysis 
3.1.1. Snow samples characterization 
For each snow sample collected in the field and conserved in iso-octane, video macrophotographic pictures

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