507
Geometric correction matrices are generated so that EROS
Data Center may continue to supply fully corrected (re
sampled) output products in several map projections:
Universal Transverse Mercator (UTM)/Polar Stereographic or
Space Oblique Mercator.
IMAGE FRAMING AND COVERAGE
The Landsat-4 orbit is 200KM lower than earlier Landsats
and provides either 7 or 9 day adjacent swath overlap of
imagery. The 16 day repeat cycle provides 233 orbit paths
with 248 potential scenes in each. Each scene covers 185KM
cross-track by 170KM in-track. The center of each scene
is identified by unique latitude and longitude points as
part of a Landsat-4 World Reference System (WRS).
The Landsat-4 WRS is quite different from that of earlier
Landsats due to the differences in the coverage cycle and
orbit inclination due to the lower altitude (see Table 3)
TABLE 3: IMAGE
FRAMING AND COVERAGE
COMPARISON
MEASURE
LANDSATS 1, 2 & 3
LANDSAT 4
ALTITUDE (KILOMETERS)
914
705
PERIOD (MINUTES)
103
99
INCLINATION (DEGREES)
98.2
99
COVERAGE CYCLE DURATION
(DAYS)
18
16
(REVS)
251
233
DISTANCE BETWEEN ADJACENT
GROUND TRACKS
(KILOMETERS)
159
172
(% SIDELAP AT EQUATOR)
14
7
ADJACENT SWATH COVERAGE
1 OR 17
7 OR 9
These differences will be observable by end users as a
slight rotation between Landsat 1, 2, 3 versus Landsat 4
imagery, and a difference in geographic coverage of each
scene.
The strategy for acquiring data when the spacecraft is not
within a line-of-sight of a ground station is also different
between Landsat 4 and earlier Landsats. Landsat 4 was de
signed to use NASA's Tracking and Data Relay Satellite
System (TDRSS) to relay data to ground stations, thereby
eliminating the need for on-board the recorders used on
Landsats 1, 2, 3. This design change was necessary since
current state of the art technology in on-board recorders
cannot support TM data rates. Use of TDRSS is also expect
ed to increase total system reliability.