Abstract:
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Bightness-temperature retrieval techniques for synthetic aperture radiometers are reviewed. Three different approaches to combine measured visibility and antenna
temperatures, along with instrument characterization data,
into a general equation to invert are presented. Discretization
and windowing techniques are briefly discussed, and formulas
for reciprocal grids using rectangular and hexagonal samplings
are given. Two known techniques are used to invert the equation,
namely, inverse Fourier transform and G-matrix pseudoinverse.
The proposed preprocessing approaches combined with these two
inversion methods are implemented with real data measured by
an airborne Y-shaped interferometric radiometer over land and
water, and are compared. The images indicate that best results
are obtained when inverting an incremental visibility obtained
after substracting a term that includes the individual antenna
temperatures, the physical temperatures of the receivers, and a
flat-target response directly measured from cold-sky looks. |