à m. INA UH a N DN era apres o peux = = E bu TEE TER NRI Le. E RIT Voy np V RR S aae i ido ———Í T 
RS LE EPA SEE RE PA ER À EN ENTE NENNT NENNEN CT TEE 
given MIF!s for ray inclinations of 0? 10,.20? and 35? for both 
tangential and radial orientation of the targets as displayed in 
Figures 2 and 3. The functions given by Wirtz refer to the Zeiss Jena 
camera and are a mean of determinations for radial and tangential 
orientations of the test target. Results of Marchant et al (1975), 
although comprehensive, are claimed to represent the MIFs for a 
reconnaissance camera, and have therefore not been adopted for this 
study. 
The extent of variations in the MIFs of the different cameras used 
in this paper will indicate the magnitude of possible variations in the 
variances derived. It is hoped that in the future a method can be 
developed for the easy derivation of the effects of different MIF's on 
the final variances of pointing; this paper is intended as an initial 
attempt at such a study. 
(v) Combined MTF of the systems. 
The combined MTF's of the 6 different systems investigated, i.e. 
cameras 188 and 189 and the super-wide angle camera with 2 different 
figures of image movement were derived by multiplying modulations 
at corresponding frequencies. Final curves determined for camera 188 
are shown in Figures 4 and 5 for low and high flying heights respec- 
tively. Image movement is the major element affecting the MTF of the 
system for the low flying heights, while the camera lens is the major 
influence on the system MTF for high flying heights. The remaining 
factors are of minor importance for these examples, but they may prove 
to be significant in other system configurations. 
2.4 Effects of Granularity 
Little research has been performed on pointing observations where 
the component of granularity has been included and analysed. Effects 
of granularity on object identification have been studied by Frieser 
and Biedermann (1963), Hufnagel (1965) and Scott (1968) as will be 
discussed in section 4. In addition, threshold modulation (TM) curves 
of emulsions as presented by Brock et al (1966) and Scott (1966) 
include all factors of the photographic emulsion including granularity. 
However Hempenius' (1964) method is more useful for this study since 
the optical magnification of the stereoplotter can be introduced as an 
additional parameter in the study. The ability to introduce the 
parameter of optical magnification is important since visual system 
performance is a function of angular subtense, which varies with 
optical magnification. By plotting the MIF's and the Modulation 
Sensitivity of the visual system (MS) on logarithmic scales the MS 
curve can be shifted laterally for changes in magnification, and raised 
on the graph to introduce effects of granularity as a function of 
target contrast and granularity. In Trinder (1973) it was shown that 
the same FL was derived for grainy and grainless photographs which were 
judged subjectively equal by Scott's (1968) observers. As a result it 
was claimed that the curves relating optimum target sizes and FL 
derived by Trinder were applicable to cases where granularity existed, 
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