urn:nasa:pds:radiosci.documentation:document:tyler.1967
1.1
Bistatic-Radar Imaging and Measurement Techniques for the Study of Planetary Surfaces
1.16.0.0
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Tyler, G. Leonard
1967
A Stanford University Ph.D. dissertation documenting use of continuous-wave
bistatic-radar for mapping planetary surfaces.
2021-08-25
1.1
Updated to IM v1.16.0.0
2021-01-18
1.0
A scanned version of the printed dissertation converted to PDF/A-1b
using Acrobat Pro DC.
Bistatic-Radar Imaging and Measurement Techniques for the Study of Planetary Surfaces
Prepared under National Aeronautics and Space Administration grant NsG-377.
No copyright.
1967
The thesis documents use of continuous wave bistatic-radar for mapping
a planetary surface. Both 'uplink' (transmission from Earth, reflection
from the planet and reception on the aspacecraft) and 'downlink'
(transmission from the spacecraft) are considered.
An electromagnetic wave reflected by a planet may be considered as a
superposition of the waves from elementary scatterers on the surface.
The ordinary radar brightness distribution, the differential radar
cross-section, the polar scattering diagram, and the radar albedo of
the surface are then all related measures of the local surface properties.
In the 'uplink' configuration the surface brightness distribution may be
determined by crossÂcorrelating the scattered fields (as measured by the
spacecraft along some fraction of its trajectory) with the expected signal
from each point on the surface. The predicted azimuthal resolution in
wavelengths is inversely proportional to the angle subtended at the target
point by the fraction of the trajectory over which the data are taken.
In range, the resolution in wavelengths is inversely proportional to the
square of the same angle. The feasibility of the method depends on use
of the illuminating wave on board the spacecraft as a frequency reference
to achieve the requisite stability.
Physical analogs of the process exist as modifications of holograms and
synthetic antenna arrays. An additional analog is that of a bank of
tracking filters, each of which is adjusted to receive the signals from
a separate portion of the surface.
The maximum likelihood estimator for the brightness of a specific
scattering area, in the presence of white Gaussian noise at low input
signal-to-noise ratios, is a Hilbert quadratic form with the expected
autocorrelation function of the signal from the scattering area as a
kernel. For maximum resolution (minimum area) this is equivalent to
the cross-correlation method for obtaining the brightness distribution.
This estimate is efficient in the sense of being unbiased and of having
minimum variance, for the low signal-to-noise ratio case.
The estimator may be realized with well-known forms of time-varying or
time-invariant filters, or with correlators. A new realization is that
of a hologram scanned with a properly weighted illuminating wave.
(Adapted from the thesis abstract)
First
English
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