rm 
MICROWAVE SIGNATURES AND MAPPING OF SNOW 
E: SCHANDA*, C. MATZLER, K. KUENZI, S. PATIL 
Institute of /, ,‘icd Physics, University of Berne, Switzerland 
H. ROTT 
Institute of Meteorology and Geophysics, University of Innsbruck, Austria 
ABSTRACT 
Ground-based and satellite-borne microwave sensors have been used to 
investigate and utilize the microwave signatures of snow. Typical signatures for 
dry and wet snow can be used to identify and quantify this types of snow. Also 
some unusual behavior of the snow cover (e.g. melt -freeze cycles, precipitation) 
can be identified by remote microwave probing. The feasibility of mapping the 
global snow cover (extent, water equivalent, onset of snow melt) has been demons- 
trated with the use of Nimbus-7 SMMR data. 
  
INTRODUCTION 
Microwave Signatures of Snow have been measured with ground-based 
instrumentation on an Alpine test site since 1977 (Mätzler et al. 1982 and 
references given therein). This long-term program of the University of Berne has 
the objective of obtaining reliable information on the microwave properties of 
the snow cover during the typical seasonal development but also to become 
acquainted with the limiting cases of unusual snow conditions. These measurements 
can be applied to the interpretation of microwave remote sensing data obtained 
from aircraft and satellites. Furthermore the large number of observed parameters 
(brightness temperatures at 5,10,21,36,94 GHz and backscattering coefficient at 
10 GHz, vertical and horizontal polarization at different incident angles) 
enable the optimum selection of instruments for remote sensing of snow. 
Statistical analyses of the microwave measurements revealed clustering of the 
data in characteristic groups and in addition scattered data points of rather 
unusual situations during distinct seasonal periods have been determined. 
Typical situations occur (1) during the winter months, December to March, 
when the snow metamorphism is low due to subfreezing temperatures, and (2) during 
the melting season when the snow surface is wet. For these typical snow conditions 
microwave remote sensing can be used to identify dry and possibly also wet snow, 
to estimate the water equivalent of the dry snow and even to determine the wet- 
ness of the surface layer. 
Unusual situations occur when (3) regular melt-refreeze cycles make 
the snow grains grow rapidly (4) radiation or precipitation effects produce ice 
lamellae (5) precipitation as rain or hail changes the snow surface. 
  
  
The effect (3) leads to unusual spectra with large changes of the 
brightness temperature with increasing frequency, the effect (4) shows large 
polarization of the brightness temperature and the effect (5) shows a strong 
decrease of the low frequency brightness temperatures with increasing rain inten- 
sity and simultaneously an increase of the backscattering coefficient. It is 
shown how these spectral signatures can be used for identifying the unusual snow 
x Presently on a sabbatical leave at the Centre d'Etude Spatiale des 
Rayonnements , Toulouse, France. 
801 
GP GB N