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;