thru each long signal, after which the form of the signal itself, aided by specialized following lenses, caused a focusing action similar to that of one of a range-distributed family of cylindrical lenses, while preserving the point separations representing ranges from the radar. The immediate result was another exposed film, this one becoming, when developed, a negative of the desired image. Measurements of the signal bandwidth, signal-to-noise ratio, the sharpness of focus, etc., were made with instrumentation that dealt directly with the image-forming illumination in the processor, avoiding the non-linearity of the response characteristics of the image film. Final films containing positive images for use by image interpreters were made from the negative-image films. The first signal film to be processed was that ground-recorded in real-time from data down-linked during the first imaging pass, made during the eighth revolution. Therefore, a preliminary evaluation of the first image film was available before much other imaging passes occurred. It showed that that first image swath began in southern Indiana and continued north-northeasterly over Michigan's the lower peninsula. Comparisons of its image with 1:250,000 USGS maps showed the location of that swath very clearly, based particularly on the positively recognizable form of distinctive windings of the Wabash River in Indiana and on the forms of nearby highways and railroads and some urban areas. This first availability of early image-content information provided an example of using feedback from the system's early image product to help control the orbiting system's later imaging passes and to allow ground crews to position calibration objects within coming swaths in time for later imaging. An unexpected bonus from the first image was the determination of the locations, lengths, and makeups of some railroad trains, plus their speeds and directions of travel. A tracking antenna and recording equipment devised for the purpose had been pre-located near enough to the expected initial imaging path so that the form of the radar pulses (very much stronger than the radar returns to the satellite) was monitored during that pass. After the orbital path had been accurately determined by observation of early images, portable equipment was rapidly shuttled to various locations within coming image swaths for similar measurements. Processed-image measurements showed that the synthetic aperture succeeded in producing resolution finer than 15 feet (5 meters) in the along-track direction, and occasionally half of that, the least possible with Quill's 5-meter-long side-looking real antenna. The