Snow cover 
Snow cover is often confused with cloud cover as indicated on the 
computer outprint of available imagery. This is of particular 
importance in mountainous areas and/or low land areas in the temperate 
zone during winter time, both for hydrologists who study the dynamic 
processes of snow melt and snow fall, as well as soil scientists, 
who want to avoid as far as possible the ordering of snow covered 
imagery. In some cases enhancement of the drainage pattern by snow cover 
may facilitate the analysis as can be demonstrated in Landsat imagery 
of an area south of Moscow in the USSR (Heuseler, 1977). 
Climate, vegetation and crops 
  
Depending upon the type of survey (soils, vegetation/crops, hydrology; 
etc.) one has to take into consideration the expected moisture conditions 
through climate diagrams (p/m or P/E) and vegetation/crop patterns 
(crop calendar). Examples of bioclimatic conditions in a tropical monsoon 
zone (India, figures 6 and T) and a marine zone (N. Germany, figures 
8 and 9) are given to illustrate the above conditions. 
The Crop Atlas of the World prepared by the Instituto Geografico de 
Agostini(Medici, d. et.al., 1969-76), Vol.I Europe, USSR, Asia Minor (1969), 
Vol.II Asia & Oceania (1973), Vol.III Americas (1970) and Vol.IV Africa (1976) 
can be of great assistance to decide on the major crops of the areas of interest. 
Climate Diagram Maps of the Individual Continents and the Ecological 
Regions of the World (Walter et.al., 1975) are also very important to 
ascertain which periods of the year are potentially favourable for data collection. 
Terminals (e.g. Silent 700 Texas Instruments Electric Data Terminal, 
cost approximately US $ 2000) connected to the retrieval system of the 
Landsat imagery held by Eros Data Center (EDC) speed up this process of 
iterative selection of the most relevant scenes for analysis. 
The European Space Agency (ESA) has recently established a data bank 
(EARTHNET) in which the data of Telespazio on Landsat as well as 
documentation on space activities in general are stored. 
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