EARTH RESOURCES OBSERVATIONS FROM SPACE - 
NASA'S EXPERIENCE AND PROJECTIONS FOR THE 1980'S 
By: William E. Rice 
0. Glenn Smith, Ph.D. 
Norman G. Foster 
Affiliation: NASA-Johnson Space Center 
Houston, Texas, USA 
Introduction 
NASA's experience in remote sensing of the Earth started very soon after 
NASA was formed in 1958. It was apparent that a satellite in Earth orbit 
would provide a new vantage point for observing the Earth. 
Although reconnaissance use of remote sensing from aircraft was well 
established, there were significant differences in the satellite program 
that NASA undertook; the greatest difference being the nature of the ob- 
ject under observation. NASA has directed its remote sensing program 
primarily at large, rather than small areas, since crops, vegetation, 
water resources, and geological features all require the observation of 
very large areas. 
A direct result of the emphasis on observing large areas has been the 
development of data interpretation by spectral characteristics rather 
than by shape. While image interpretation by shape works well when 
distinguishing man-made features and specific objects in relatively 
small areas, it would be impractical with current technology to cover 
an entire country's corn crop, for instance, with imagery of resolution 
high enough to identify the corn fields by the shape of the vegetation. 
The development of the calibrated multispectral scanner has permitted 
the identification of many Earth features by their spectral characteris- 
tics. Two advantages result from this development: first, areas on the 
ground which are spectrally similar can be identified as a unit; and, 
secondly, and most important, the process of spectral identification can 
be largely automated and performed by computers. 
The unique features of satellite remote sensing are: 
a. synoptic view; 
b. near global coverage;