provided X- and C- band data with HH and VV 
polarizations each. The maximum snow cover 
data were acquired on March 20th, 1991. At 
this time only the C- band was available, but with 
polarization of HH, HC, CC, and CH. The 30° 
and 60° incidence angle coverage required the 
use of the RADAR in 'nadir' and in ‘narrow’ 
modes respectively. 
Ground Data Collection. 
Since the SAR imaging was carried out at the 
afternoon after a snow storm the ground data 
collection could not be started until the next day. 
In total 13 different sites were extensively 
surveyed. In each site one or two parallel lines 
were laid out and at 6 m intervals the snow 
depth, density, and SWE were measured. In 
addition one or two snow pits were dug along 
each test lines and the following data collected in 
the pits: number, thickness, temperature, snow 
density, crystal structure, hardness, and grain 
size of layers. All work was extensively 
documented with ground and large scale aerial 
photographs and video. 
In October, 1991 detailed field work was 
performed to analyse the underlying surface of 
each test site. 
DATA ANALYSIS 
Digital data and pictorial output for each flight 
line was provided by CCRS. In addition 
absolute calibration functions were worked out 
by CCRS scientists using the images of the 
deployed corner reflectors. 
Ground Data. 
The raw field snow measurements in each station 
of all test lines were converted into SWE and 
plotted over a sketch of the underlying ground 
cover types. The distribution of snow depths 
and SWE-s (min. max. and average) are 
presented in Table 2. The snow pit data were 
analysed for snow layer structure determination. 
A sample pit structure is given in Figure |. 
38 
  
  
Ambient Temp. -16 C 
70— RAS, 
Layer 3 
60— -14 C 
SWE = 5.3 cm 
50— 
Een dE ee ee AT) 
tof 40— Layer 2 
5 -6.5 C 
E 307 SWE = 6.2 cm 
e Solid Crust 
e 
20— Layer 1 
SWE = 7 cm 
10— 
-2C 
0— 
  
  
  
  
  
  
  
Figure 1. Profile of snow pit G 3. 
SAR Data. 
Based on flight recordings the incidence angles 
for each test sites were calculated (Table 1). 
An in-house computer program was written to 
read, display, and dump the digital data provided 
by CCRS. This program involved a pictorial 
display of the image from which the areas of the 
test sites could be chosen for dumping of the 
digital data. Another program was prepared to 
carry out the conversion of digital numbers to 
power (c) and average RADAR cross section 
(09) for a selected sub sample. A third program 
provided the averaging of 9 neigbouring pixel 
values (3 by 3 kernel). As an illustration for one 
of the test areas (green 3), the raw and the 
fillered digital numbers (DN) of pixel values 
obtained by the SAR (nadir mode HH 
polarization) with the corresponding SWE data 
are given in Table 3. 
International Archives of Photogrammetry and Remote Sensing. Vol. XXXI, Part B7. Vienna 1996 
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