A target database plays a key role in automatic target recognition (ATR) using SAR images. To construct a target database, indirect information of the targets such as plastic models, 2-dimensional draft and pictures of them can be used to make target 3-dimensional CAD models when real targets are not accessible. Each one of the indirect information is not enough to extract the accurate shape information of targets and they should be used together to make the 3D CAD models more accurately. We used 3D graphics models that are available on the internet, 2D drafts with size information and many pictures of targets at various aspects to reverse-engineer the 3D shape of the targets in detail. This paper proposes a practical target 3D CAD modeling method using the indirect information of a target and shows the results by comparing the 3D CAD models made with indirect information with the models generated by high precision laserscanning method. In addition to comparing the 3D shape itself, RCS calculation, ISAR imaging, scattering center extraction with electromagnetics (EM) analysis code were adopted to inspect how the difference of two models affects the scattering phenomena and SAR images as a result. The result shows that once we experience the building-comparingcorrecting process several times for the generation of accurate target CAD models, decent level of target CAD models can be made using indirect information only.
KEYWORDS: Scattering, Computer aided design, Solid modeling, 3D modeling, 3D acquisition, Databases, Data modeling, Laser scanners, Radar, Data centers
In this paper, a method to obtain 3-dimensional Computer-Aided Design (CAD) models of radar targets from their real
shapes is proposed for the construction of a database which is composed of scattering centers of the targets and a
consideration of an efficient formation of the database from the appropriate collection of Radar Cross Section (RCS) data
is also described. As 3-dimensional CAD models of the targets are not available in many cases, a method to make a
geometric model from the real target is needed. Three dimensional coordinates of the target can be measured by a laser
scanner. These measured coordinates are combined to form a 3D CAD model of the target. With the CAD model
obtained, RCS values of the target are calculated over a series of frequencies and angle apertures to be transformed into
scattering centers by a superresolution technique, which is Matrix Pencil (MP) in this case. The CAD model of an airtarget
is utilized for the test to infer the criterion on the frequency of the sets of extracted scattering centers for the
optimal database construction, where RCS data sets are calculated every 5, 10, 15 and 20 degrees in azimuth direction to
be used for the scattering center extraction. And then, RCS values are reconstructed from those sets of scattering centers
to compare with the original RCS values of the target to determine how many sets of scattering centers our database
should have over the whole azimuth angles. The result show that the smaller the angle gap between the adjacent sets of
scattering centers, the better match between the original RCS and the reconstructed RCS.
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