Since it has been found that the allowable magnification can be doubled, the allowable terrain relief 
should be reduced by one half. The spacecraft sensor systems which were considered in the 1971 
paper were : 
ERTS RBV ERTS MSS SL-S190A SL-S190B 
Sensor Vidicon Scanner Frame camera Frame camera 
Record, format 60 x.60 mm 60 x 60 mm 58 x-58 mm 115 x 115 mm 
Record scale 3 :370 000 3 370 000 2 900 000 945 000 
Ground resolution 180 m 300 m 40 m 10m 
Coverage per frame 185 x 185 km 185 x 185 km 174 x 174 km 108 x 108 km 
Based on these parameters the following orthophoto map products were anticipated. 
ERTS-RBV ERTS MSS SL-190A SL-190B 
Map scale number 1 000 000 N 250 000 62 500 
Format 69 x4? O 29x11? 15!:x 15" 
Photos per sheet 12-15 N 2-3 1-2 
Map resolution 6 1p/mm E 7 1p/mm 6 1p/mm 
Cartographic Products from ERTS 
  
The characteristics of the ERTS satellite are, by now, well known [2]. The vehicle flies 
in a circular orbit with 915 km altitude and 97° inclination. It makes 14 revolutions per day and 
every 18 days the entire Earth (except for the polar areas) passes beneath its Return Beam Vidicon 
(RBV) and Multi Spectral Scanner (MSS) sensors. 
The RBV is a 3 spectral channel frame format television system. Before launch it was 
anticipated that the RBV would have better ground resolution and much superior geometric fidelity 
than the MSS. It was contemplated that mapping would be done exclusively with the RBV. However 
a few days after launch the RBV was shut down because of electrical switching problems and has 
not been reactivated. 
The MSS has an oscillating mirror which reflects the scene through a Cassegrain teles- 
cope to a series of detectors. The image is recorded in 4 spectral bands : green, red, and two 
near infrared bands. The scanning aperture projected to the ground has a diameter of 79 meters. 
This is equivalent to a photographic resolution of 220 to 320 meters depending upon the scene con- 
trast. The scanning motion covers a cross track swath of 185 km and spacecraft motion provides 
a continuous picture along track. 
The spacecraft also carries a tape recorder to store scenes acquired when the spacecraft 
is out of range of the ground stations. 
The S-band signals transmitted from the spacecraft are recorded on tape at the ground 
stations and sent to NASA Goddard Space Flight Center for processing. An Electron Beam Recorder 
(EBR) prints each spectral band as a separate black-and-white image on 70 mm roll film at an 
image scale of 1:3 370 000. The MSS images, though recorded continuously on the spacecraft, are 
printed as 185 x 185 km scenes by the EBR. During this process certain geometric corrections are 
applied which make the picture equivalent to a perspective picture of a flat stationary Earth. The 
separate black-and-white bands are photographically enlarged to scale 1:1 000 000 and combined 
to produce the tonal response of color infrared film. 
In its more than 2 years of operation ERTS-1 has returned about 140 000 scenes, each 
recorded in 4 spectral bands. Cloud free coverage has been obtained for about 80 percent of the 
Earth's land mass. Many areas have been recorded numerous times in all seasons of the year. 
However in recent months the tape recorder has been progressively deteriorating and pictures 
can now be obtained only for those areas which are within range of the receiving stations in Alaska, 
Canada, the United States, and Brazil. 
Tests performed on the early images received demonstrated that the actual resolution 
was about 250 m for low contrast images on both the RBV and the MSS [3]. 
After the failure of the RBV system, cartographers were faced with the problem of attemp- 
ting to make maps with the MSS records. Built into the NASA ground data handling system is an 
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