The change to TDRSS does effect the initial Landsat 4 
coverage since TDRSS will not be operational until 1983. 
Until that time, Landsat 4 imagery will be limited to areas 
covered by selected existing ground stations as shown in 
Figure 1. 
The sidelap of imagery between adjacent paths is less than 
the earlier Landsats. In addition, the ground control 
points used as part of the geometric correction process 
from earlier Landsats have been resampled and converted 
for Landsat-4 use. 
GEOMETRIC CORRECTION 
The purpose of geometric correction is to locate image 
samples such that: 1) the locations are known with res 
pect to a map grid reference system (geodetic rectifica 
tion) and 2) each satellite pass over an area may be 
digitally registered to a reference pass (temporal regist 
ration). The Landsat-4 system has been designed to provide 
the following accuracies for both MSS and TM imagery: 
geodetic: 0.5 pixel (90% of the time) 
temporal: 0.3 pixel (90% of the time) 
These values are essentially the same requirements that the 
Landsat 2 and 3 Image Processing Facility (IPF) was de 
signed to meet. The only known controlled measurement of 
accuracies (performed using 22 ground control points by 
the DOI Geological Survey) indicates that the mean geodetic 
error is 1.4 pixels with a 2.0 pixel standard deviation. 
Likewise a registration mean error of 1.0 pixel with a 
standard deviation of 0.7 pixels were determined using 23 
ground control points over a pair of scenes analyzed at 
Goddard Space Flight Center. 
There is both good news and bad news with respect to the 
Landsat-4 geometric correction potential. With respect to 
the spacecraft, the bad news is that MSS design was modi 
fied slightly to account for the lower orbital altitude. 
This provides larger mirror scan angles, higher scan mirror 
velocity and hence potentially greater scan nonlinearities. 
To correct for these errors, the models used in the geo 
metric correction process have been enhanced. Also, the 
spacecraft platform is a new structure and is faced with 
many sources of vibrational excitation such as: the scan 
mirrors from both the MSS and TM; the solar array pointing 
system; and the Tracking and Data Relay Satellite System 
antenna pointing system (see Figure 2). Preliminary 
analysis of the Landsat imagery indicate that these sources 
of error will not exceed the .3 pixel temporal registration 
accuracy requirement. 
The good news is that the spacecraft has a better attitude 
control and measurement capabilities. The attitude control 
system has more accurate pointing (7 to 1 improvement) and