Evaluation of Resolving Power and MTF of DMC

The present article reports the results of an extensive empirical evaluation of spatial resolution of a digital large format Intergraph DMC sensor. The parameters of the study were flight direction, ground sample distance (GSD) and the distance from the image center. The key finding of the study was that the resolution of the DMC panchromatic large-format image was clearly dependent on the distance from the image center. One reason for this behavior is that the DMC large-format image is composed of four oblique images; the resolution of the oblique images is reduced towards the image border due to the scale reduction and projective distortion. From the image pixel size of 12 µm of DMC, a nominal resolving power value (RP) 84 lines/mm can be derived. Maximal resolution reduction factors in the image corners, caused by the image tilt, were 1.6 in the cross-flight direction and 1.4 in the flight direction. The distance from the image center did not appear to affect the resolution of the low-resolution multi-spectral images looking towards nadir. The observed MTFs indicated attractive behavior. The AWAR values of the panchromatic images were between 61 and 71 lines/mm, which is 1.2-1.4 times the nominal RP-value. Other important findings were the effects of GSD and flight direction on the resolution; these properties evidently characterize the behavior of the entire photogrammetric system tested. The image restoration by a linear restoring finite impulse response filter provided a constant resolution improvement factor of 1.4.