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moved without inducing other errors. Therefore, to remove 
the original major position error source by improving the 
attitude accuracy will reduce the registration error, 
thereby achieving subpixel registration if the ephemeris is 
essentially perfect. 
REGISTRATION ACCURACY 
Specified accuracy within 0.5 pixel of geometric correction 
(90# of the time) and accuracy within 0.3 pixel of temporal 
registration (90# of the time) are required for Landsat-D 
MSS and TM images, respectively. Assume that the future 
Multispectral Linear Array (MLA) type data is required 
within subpixel accuracy for registration. As a digital 
image is mapped onto a reference image of the same scene by 
means of registration, the cartographic accuracy for map 
ping is relevant and can be used to obtain registration ac 
curacy requirements. If these requirements are satisfied, 
registration errors are acceptable. 
In cartographic applications, accuracy is normally defined 
in terms of RMS for the residual errors resulting from a 
measure of variations from the correct locations at check 
points with respect to a map or to a given reference. To 
determine the RMS residual error, let d be the residual er 
ror or the difference between the correct coordinate value 
(xi, y.) of each control point on the map and its corre 
sponding coordinate value (x: # , y/ ) as determined from its 
location measurement in the image. The RMS of residual er 
ror i s 
V = I (1/n^di 2 (1) 
J i = l 
where d^ 2 = (Xj.* - x^) 2 + (Yi - Yi)^ 
and n equals a large number of points over an image. 
For a finite set of points (x, y) the value of V so obtain 
ed is usually defined at the 68# level of confidence. By 
using normal distribution, the total RMS of the residual 
error contained in an image at the 90# level of confidence 
is 1.65V. Therefore, registration accuracy requirements 
for scene-to-map registration and scene-to-scene registra 
tion can be expressed mathematically. If P represents the 
pixel size (each dimension) in meters, two equations are 
formulated directly from these requirements. 
As previously stated, the scene-to-map registration (recti 
fication or geometric correction) accuracy is required 
within 0,50 pixel (90# of the time); therefore, we have 
1.65 V ^ 0.50 P 
V ^ (0.50/1.65) P = 0.30 P 
We may define 0.30 P as the maximum allowable scene-to-map 
registration error, which is 24 m for the MSS data, 9 m for 
the TM data, and 3 ni for the MLA data.