p 1 
ZO POSER STE PRO NES TE TO i 
A possible alternative approach involves the determination of an 
area-weighted average modulation (AWAM) value determined by integrating 
over the area bounded by: 1) the average of the tangential and 
sagittal MTF's for given field positions (i.e. the average lens MTF 
at each of several specified format positions); 2) a TM curve for the 
eye; and 3) a limiting spatial frequency based on the intersection of 
the eye TM curve with the lower MTF (sagittal or tangetial) curve at 
a given field position. Quality values based on this approach rank 
Systems similarly to resolution values and are more sensitive to 
system perturbations. For the user, the MTF at the point midway between 
zero and the limiting spatial frequency was found to correlate with 
visual impressions of image quality. (é 
MTF's are proving useful for testing lenses and offer promise as a 
basis for image quality criterion. The phase component, included in 
the specification of OTF, remains troublesome and is often omitted in 
tests of photogrammetric lenses. Practical procedures for utilizing 
phase measurements to assess lens distortion remain to be determined. 
Optical and Electro-Optical Sensor Systems 
Investigations of earth resources and cartographic applications 
with small-scale satellite images have resulted in numerous discussions 
on the advantages and limitations of three groups of sensor systems: 
1) high-resolution film cameras (e.g. the Itek Large Format Camera 
and the Zeiss RMK A 30/23 camera to be employed on the Space Shuttle/ 
| Spacelab experiments); 2) RBV's and mechanical scanners (such as the 
| RBV's and MSS of Landsats -1, -2, and -3, and the Thematic Mapper of 
Landsat-D); and 3) solid-state array sensor systems (proposed for 
Landsat and Stereosat missions). Of these systems, those incorporating | 
solid-state array and charge-coupled device (CCD) technology have qo 
evolved rapidly since 1970. Solid state array detectors can be used 
| to sample images in either one or two dimensions and because of their 
| small-size, lightweight and high-sensitivity are being considered for 
| future earth resources satellite sensor systems. At present, arrays do 
| not rival film in terms of resolving power, however, they do provide 
| improved signal-to-noise ratios and a linear input-output response over 
| a wide dynamic range. Consequently, the array camera is likely to be 
| preferred for tasks requiring the thematic classification of the ground 
scene from digital reflectance data, whereas, the film camera, with its 
high visual resolution limit, is superior for cartographic applications. 
Major areas under investigation include tradeoffs between scanner and 
array detector systems, measures of system performance and data quality, 
influence of image-forming optics and data processing/handling systems 
on data quality, and the photogrammetric/remote sensing potential of 
multispectral linear arrays (stereo and non-stereo).