Averaging-area-constrained adaptive interferometric filter that optimizes combined coherent and noncoherent averaging

DETAILED DESCRIPTION To meet the above and other objectives, the present invention provides for adaptive filters and filtering methods for use with coherent computed imaging systems.
The adaptive filters and filtering methods support processing of interferometric phase measurements made with coherent computed imaging systems.
Interferometric synthetic aperture radar (SAR) are a special case of such coherent computed imaging systems that are of particular interest and for with the present invention may be advantageously employed.
More specifically, the present invention provides for a family of multiple scale adaptive filters which automatically adjust their impulse response width to local data characteristics, optimizing the accuracy of the interferometric measurement.
The adaptive filter disclosed in U.
S.
Pat.
No.
5,488,374 is extended in accordance with the principles of the present invention to satisfy a common requirement for producing output measurements having a fixed averaging area, that is, to produce a digital elevation model (DEM) with independent posts on a uniformly-sampled grid.
To achieve this requirement, an adaptive prefilter designed to optimize coherent averaging (i.
e.
, filter a complex interferogram) is coupled to a postfilter applied noncoherently after phase unwrapping of the complex interferogram.
The postfilter adjusts its impulse response locally in inverse relation to the impulse response width of the coherent adaptive prefilter, maintaining a spatially-invariant averaging area.
The present filter thus automatically adjusts the mix between coherent and noncoherent averaging to maintain the accuracy of interferometric measurements under the broadest set of conditions while satisfying a constant averaging area requirement.
The present invention may be employed in reconnaissance and remote sensing systems, such as interferometric synthetic aperture radar systems, and the like.
Potential candidate systems developed by the assignee of the present invention include SIVAM, HISAR, ASARS-2, Global Hawk, ARL-M, for example