Since the scene-to-scene registration (temporal registrat 
ion) accuracy is required within 0.3 pixel 90# of the time, 
the equation becomes 
1.65V ^ 0.30P 
or 
V ^ (0.30/1.65)P * 0.18P (3) 
where ,18P is defined as the maximum allowable temporal 
registration error. This error is 14.4 m for the MSS data 
5.4 m for the TM data, and 1.8 m for the MLA data. In 
order to meet these constraints, it is required that the 
acceptable registration error not exceeds the corresponding 
maximum allowable registration error. This requires that 
the acceptable temporal registration error not exceeds 1.8 
m for the MLA data. These maximum allowable errors are 
much smaller than the image position error generated by 
attitude uncertainty 
Evidently, the current attitude accuracy is not consistent 
with subpixel registration accuracy requirements without 
control points even when the on-board attitude system per 
forms within its technical specification. The difference 
between the registration error remaining in the corrected 
image and allowable registration errors is significant. 
Both General Electric (G.E.) and E-System performed stud 
ies on the temporal registration of Landsat-3 MSS data. 
The G.E. study revealed that subpixel accuracy of the MSS 
data had not been demonstrated by the current processing 
system (reference 7). Studies of registration accuracy 
for the TM and future MLA type data by E-System Garland 
Division and others have led to similar conclusions. These 
studies show that the reduction of remaining registration 
errors to an acceptable error level for higher resolution 
data has not been achieved by the existing processing 
systems. Furthermore, registration accuracy requirements 
will not be met if the pointing Information is not supplied 
adequately. Attempts to improve Just the ground processing 
system will serve to Increase its cost and will not provide 
the accurate pointing knowledge, if the on-board attitude 
control and determination system (attitude system) remains 
the same. A more fruitful approach to achieving the goals 
for higher resolution would Involve the improvement of both 
the ground processing system and the on-board attitude 
system. 
ATTITUDE UNCERTAINTY 
To obtain accurate pointing knowledge of the Instrument, 
an approach is to improve the on-board attitude system to 
increase its capabilities. Thus, attitude uncertainty can 
be reasonably reduced, minimizing the need for the costly 
and tedious build-up of ground control points for image 
registration. It should be noted that considerable time 
is needed in the processing of GCP s. Based on the study 
report (reference 10, page 101) approximately five man- 
days are required for ten GCPs. The cost of each GCP to 
become available for image processing is now much more than 
$100 (reference 4).