ll. Advantages 
The most important advantages of snowmapping from satellite imagery are that 
they offer: 
- a simultaneous view of very large areas, allowing a truely regional or 
even global comparison (which is impossible on the ground or even from | 
aerial photography); | 
- à continuous surveying of the study area in short time-intervals 
(repetition rates between 12 hours to 9 days); 
- a surveyance of areas which are remote and inaccessible; 
- a surveyance of the polar areas during the periods of darkness (using 
thermal sensors and SAR in the near future); 
- the classification and separation of a single object from all other 
features (in contrary to e.g. land-use where a variety of elements has 
to be classified). 
HI Objectives 
Surveying and measuring the snowcover with satellite techniques may be under- 
taken for quite a many different purposes, which may be of purely scientific 
interest or for predominantly applied studies, asking for an operational 
status of the methodology to be used. The main reasons for snowcover moni- 
toring are listed in Fig. 1. 
The applied method(s) should always be adequate to the objectives of the 
study and hence will vary accordingly. In particular the method has to be 
applicable under all different conditions (sun, shadow, relief, vegetation 
cover etc.). 
IV Snwoparameters to be observed and/or 
measured 
To gain the necessary background information for the accomplishment of the 
various objectives as mentioned above (Fig. 1), different snowparameters as 
well as other features should be observed and/or measured from remotely 
sensed data, such as: 
- areal extent of the snowcover in its seasonal variation 
- snowdepth 
- water equivalent 
- surface conditions: 
= snowtype 
= temperature