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Short range direct-path measurements are used to perform diagnostic imaging measurements on portions of aircraft (or ships or vehicles, etc.). We call them ``direct" because the range is short and the radar signal does not have time to bounce off the ground. For longer-range measurements, see Ground-Bounce TRACKSAR measurements.
It is convenient to make these measurements with a short track, which is easily handled. The track shown in this picture is 2.5 m long.
Normally, the resulting image is equal in width to the length of the track, although METRATEK processing software can bypass this limitation, allowing a much shorter track to be used.
The F-18 tail empennage below has rows of fastener holes along both edges and several defects along the middle; only one penetrates the surface. The image was taken with the 2.5-m track at X-Band in an ordinary room with 8-foot ceilings. Resolution is 4 cm and the defects are clearly visible as a white spot and several blue ones along the centerline of the piece. Note the strong (white) returns at the leading and trailing edges.
F-18 Composite Tail Empennage with Defects
TRACKSAR Image Showing Fastener Holes and defects
TRACKSAR resolution (its ability to distinguish between nearby targets) can be calculated from the following equations:
Downrange = c / (2 * bandwidth) = 15 cm / bandwidth in GHz
METRATEK radars use spotlight SAR, i.e. the radar antenna tracks the center of the target as it proceeds down the track; otherwise, the antenna pattern can degrade the cross-range resolution.
The Model 200 track shown below is being used to measure a large aircraft inside a hangar. The fork lift allows fast positioning of the track. The radar can be seen behind the track on the right side; a 50 foot cable allows the core module to be separated from the RF Head.
Copyright METRATEK, Inc. 1998, all rights reserved
