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REMOTE SENSING AND INTERPRETATION 
Robert G. Reeves * 
U.S. Geological Survey 
Remote sensing encompasses a wide variety of techniques, including 
electromagnetic geophysical surveys, gravimetry, gamma radiation 
surveys, and electromagnetic radiation (EMR) sensing methods. In 
the United States the term is generally applied to that part of the 
electromagnetic spectrum with wavelengths between about 0.3 micro- 
metres and 1 metre. Although some remote sensors produce numerical 
point data (radiometric temperature, reflectance percentage, spectrom- 
etry, and scatterometry), the bulk of remotely sensed data is in the 
form of imagery, and this report is concerned primarily with recent 
developments in the acquisition, interpretation, and applications 
of imagery. 
IMAGE ACQUISITION PROGRAMS 
Landsat 
The first Earth Resources Technology Satellite ERTS-1 (renamed Iandsat-1 
in January 1975) was launched on July 23, 1972. The spacecraft, payload, 
orbit, and processing of Landsat data are described in NASA publication 
(1972). Landsat-2 with identical psrameters was launched on January 22, 1975. 
Landsat-1 and-2 have identical sensor payloads: a three-unit return- 
beam vidicon (RBV) system and 4-channel multispectral scanner (MSS). 
Imagery from these sensors covers an area 185 by 185 km. The RBV** 
takes pictures in the green (0.475-0.575 um), red (0.580-0.680 um), 
and near infrared (0.690-0.830 um) bands. The MSS channels are: 
0.500-0.600, 0.600-0.700, 0.700-0.800, and 0.800-1.100 um. The 
several bands can be combined in different ways to produce a color 
composite resembling & color-infrared photograph. 
Landsat data may be acquired and transmitted directly to a ground 
receiving station when the satellite is within range. When the satellite 
is not within range of a ground receiving station, the sensors are 
controlled by a preset program and the data are tape recorded on the 
satellite and transmitted to the first U.S. ground receiving station 
  
¥Roger M. Hoffer, Gerald K. Moore, Wayne G. Rohde, Donald S. Ross, 
and Robert K. Vincent have contributed to and reviewed this report; 
their assistance is gratefully acknowledged. 
**The RBVs were deactivated shortly after launch due to a switching 
problem on Landsat-1. They have been used only for system checkout 
on Landsat-2.