1000 miles (1600 km), a length limited by the maximum distance at which the satellite remained above the tracking station's horizon. The capture of data for that swath occupied only 3.6 minutes of orbit time. Data processing Three methods of image data recording were used. The highest-quality data was displayed on an on-board cathode ray tube and recorded on photographic film. Recovery of the on-board film was by the method used for the then-current U. S. photo satellites, which was to eject a re-entry package containing the exposed film and capture the package in mid-air as it descended under a parachute. Since that process did not take place until after Quill's first seven imaging sequences, images from down-linked data were both the first and the last to be available. Down-linked data was ground-recorded in real-time on similar films and also on magnetic tapes. The early availability of those films allowed image interpreters to observe the boundaries and contents of early image swaths before the on-board film was released from the satellite, a capability not then possible with optical film-camera sensors. Data returned by down-link was of reduced quality due to the characteristics of the down-link, so that signal films exposed on the ground from that data had to be of lower quality than that simultaneously exposed on board. Signal films made later from magnetic tape recordings of the down-linked signals suffered somewhat more. Signal film from all of the three recording sources was developed at a ground processing facility. At that point, the optical appearance of the SAR data on the film in no way resembled an image of the terrain illuminated by the radar. Instead, it appeared visually nearly like noise, except that it was striated lengthwise of the film. Each striation represented a different radar range and contained long sequences of overlapping radar-return signals from many (literally thousands) of terrain points at that range. Further data- processing was needed to separate those signals from each other and to create, from each of the many distributed signal contributions, one spot of the proper intensity at each image point corresponding to a terrain point. At that time, the only technique available for the job was a high-quality optical data-processor (the Precision Optical Processor, or POP) that had been developed specifically for both airborne and orbiting SAR systems. That data-processor converted the information on the signal film by passing laser light