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SATELLITE SYSTEMS FOR CARTOGRAPHY
Frederick J. Doyle
U. S. Geological Survey
Reston, VA 22092, USA
ABSTRACT
Mapping from remote sensing records requires image information content
and geographic referencing accuracy which are related to the scale of
the published map. However the extraction of cultural planimetric de
tail requires a ground resolution of about 3m/£p or 1.5m/pixel regard
less of the scale of the final map. The requirements for 1:50,000-
scale mapping are not met by Landsat-4 or the SPOT system. The Metric
Camera experiment on Spacelab-1 and the Large Format Camera currently
planned for Shuttle Missions STS-11 and STS-17 will both provide re
covered film data suitable for mapping at 1:50,000 scale. An electro-
optical system called MAPSAT has been proposed by the U. S. Geological
Survey to meet the same requirements.
INTRODUCTION
From the earliest days of the space program cartographers have expected
that photography from space vehicles would result in the same increment
of productivity which came about when aerial photography replaced ground
surveys. Photographs from the early manned missions, Mercury, Gemini,
and Apollo provided spectacular views of the Earth, and experiments
showed that it would be possible to assemble image maps at scales of
1:250,000 or smaller, but that the resolution would be inadequate for
compiling roads, railroads, urban areas, and other cultural features
which one normally expects to find on maps, regardless of their scale.
Partly as a consequence of this deficiency, partly for fear of politi
cal implications of high resolution photography, but mostly in response
to a perceived need for classifying land use, geologic structures, and
agricultural productivity on a countrywide basis, the Landsat systems
were not designed for topographic mapping. It is the purpose of this
paper to address the problem of topographic mapping from space.
RESOLUTION REQUIRED FOR MAPPING
The fundamental content of a photogrammetric map is provided by ground
resolution of the images, expressed in meters per line pair for photo
graphic systems, or in meters per pixel for electro-optical systems.
There is a direct relationship between ground resolution and the useful
scale at which images can be reproduced. (Doyle, 1973)
The resolving power of the normal human eye at usual reading distance of
25 cm is about 7 line pairs per millimeter (£p/mm). Thus the smallest
dimension which can be observed in the image is 1/7 mm, and for photo
graphic systems the relationship between ground resolution R m (in m/£p)
and image scale number S m is given by
^m
which may be rewritten
1 mm 1 m e
7 £p 1000 mm m
S m = 7000 x R m
(1)
