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n X-band
foreign
ground stations are currently configured to receive and process the 85 megabits/
second X-band data, though several have indicated their intention to do so. First
will be the Canadian station at Prince Albert to provide TM coverage of the
western United States. The separate TM processing system at GSFC will be operated
by NASA, initially on an experimental basis producing one or two scenes/day by
the first quarter of 1983, and full capacity of 50 scenes/day by 1985. GSFC will
produce both film and CCT products. EDC will receive film from GSFC and will
supply photographic products to users, but CCTs will be supplied directly by
GSFC. NOAA will assume operational responsibility for TM data when full capacity
of the ground processing system has been adequately demonstrated.
An identical spacecraft, Landsat-D prime, will be ready for launch about July
1983. It is hoped to add wide band video tape recorders for the MSS on this
spacecraft, but funds have not yet been provided for this modification. Accord-
ing to present plans, the spacecraft will not be launched until Landsat-4 begins
to fail. Since the specification lifetime for the TM is two years and for the
MMS is three years, this plan should provide data through 1986 to 1988. By that
time, NOAA is expected to have reached an agreement for commercial operation of
the Earth observation satellite systems. Both Landsat-4 and D prime are equip-
ped for recovery and possible relaunch by the Shuttle, and a Shuttle mission has
been designated for this purpose in 1986-7. However this may not actually be
done because of the prospect of commercial operation using a different system
configuration. NOAA has proposed that they be authorized to operate the system
if an acceptable contract cannot be reached with a commercial venture, but this
has not been approved and no federal funding is anticipated after Landsat-D prime.
Experimental electro-optical sensors
One of the most promising imaging sensors is the linear array of charge coupled
detectors (CCD). These arrays consist of several thousand elements and they
can be butt-joined to provide more than 10,000 detectors per line. An optical
system images a line from the ground scene to the line of detectors. Ground reso-
lution in the cross-track direction depends upon detector size and the ratio of
optical system focal length to flight altitude; in the along-track direction it
depends on the time in which the signals can be recorded as the vehicle moves
along the orbit. NASA has undertaken several studies of possible sensor instru-
ments using this concept. Recently completed is the MLA (multispectral linear
array) Instrument Definition Study. The study proposes use of the MMS launched
by Shuttle into a Landsat-4 orbit. The sensor instrument would provide six
spectral bands in the visible and shortwave infrared. Five of these would have
30m IFOV and one band in the red would have 15m IFOV for recording cultural
features. The optical system would provide +/-26° fore and aft stereo viewing
and */-309 across track pointing for missed scene recovery. The data rate would
be 200 megabits/second with onboard storage and data compression, and transmission
direct to ground and via TDRSS. NASA has awarded several contracts for the design
of an experimental demonstration instrument to be available for flight on the
Shuttle by about 1988.
MAPSAT
The U.S. Geological Survey, concerned about the technical and economic viability
of systems as complex as Landsat-4, or the NASA MLA Instrument concept, has
completed a study for a system called MAPSAT which would provide data adequate
for compilation of 1:50,000 scale maps with 20m contour intervals. The orbit
would be the same as Landsat-1, -2, and -3. Three MLAs would look in the vertical
and -/-239 fore and aft to provide stereo data. Each array would have three spec-
tral bands and a minimum 10m IFOV, but the information could be clustered by on-
board processing to provide lower resolution at multiples of the 10m IFOV. On-
board data compression and selected acquisition would reduce the data rate to
48 megabits/second which can be accommodated by minor modifications to the
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