Table 3. Ground and SAR Data For Target 
  
  
  
  
  
  
  
Area G3. 
Ground SWE Digital 
Sheet # (cm) Number 
Raw Filtered 
65 
reflectors | 103 
43 
22 
22 
1 21 24 30.0 
9 19 36 312 
3 23 31 28.4 
4 22 23 253 
S 24 22 28.8 
6 25 41 33.0 
7 25 35 34.1 
8 24 25 30.7 
9 17 25 27:7 
10 25 25 26.7 
11 24 29 26.2 
12 21 24 25 4 
13 20 24 284 
14 2 24 25.8 
15 22 30 25.0 
16 17 17 271 
17 
25 
39 
reflectors | 126 
108 
ze eio > 
je 
20 + 
  
  
  
  
T 
10 
T 
15 
T T 
20 25 
DN (nadir, HH) 
T 
30 
T 
35 
T 
40 
45 
Figure 2. Linear regression of SWE vs.DN-s 
Similar equations were developed for each test 
area, both with HH and VV polarizations. 
RESULTS 
The ground survey gave detailed information on 
snow distribution (depth, density, SWE) and on 
the underlying ground cover (soil rock, ice, 
vegetation type). The SAR data must be 
correlated with all of the snow parameters, the 
underlying surface conditions and with the 
incidence angle and polarization of the RADAR. 
Since the preparation of the necessary computer 
programs and the development of the absolute 
calibration procedure took a very long time, the 
data has only been partially analysed to date. 
Ground Data. 
We had a very good distribution of SWE within 
and between test lines (Table 2). The snow 
depth should be over 20 cm to have an effect on 
the SAR return. In our case this varied between 
3] and 138 cm. The SWE vaiues had a range of 
9 to 38 cm with averages of 12.9 to 24.5 cm of 
individual test lines. 
The snow pit data provided detailed information 
on snow layering characteristics. All 22 detailed 
snow pits had at least 3 distinct snow layers. 
Thirty two per cent had four distinct layers and 
only one pit had five distinct snow layers. The 
mean thickness of the three main snow layers 
from the bottom of the pit to the surface was 22, 
25, and 24 cm respectively. In the snow layer 
closest to the substrate, the snow temperature 
showed the least variation and averaged -1.5 °C. 
The temperature of the snow in layer three near 
the surface was very close to the ambient 
temperature. The SWE variation was minimal in 
the layer close to the substrate and highest in the 
second snow layer with variation further 
decreasing in the newer snow on top of the 
profile. 
SAR Data Correlation With Ground Data. 
The C- band SAR return from snow covered 
areas is made up of volume scatter from the 
International Archives of Photogrammetry and Remote Sensing. Vol. XXXI, Part B7. Vienna 1996 
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