1015
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.
Sensor
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
SPOT XS
Cl: 0.50-0.59 pm
20 m x 20 m
60 km
C2: 0.61 -0.68 pm
idem
C3: 0.79 - 0.89 pm
idem
Push-Broom
Cl: 0.51 -0.60 pm
2 m x 2 m
4 km
C2: 0.61 - 0.72 pm
idem
C3: 0.76 - 0.95 pm
idem
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 - DATA PROCESSING
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
