Conventional synthetic aperture radar (SAR) Coherent Change Detection (CCD) has been found to be of great utility in
detecting changes that occur on the ground. The CCD procedure involves performing repeat pass radar collections to
form a coherence product, where ground disturbances can induce detectable incoherence. However there is always a
difference in the radar collection geometry which can lead to incoherent energy noise entering the CCD. When sensing
flat terrain in a far-field regime, the incoherence due to collection geometry difference can be removed through a
conventional global Fourier image support trimming process. However, it has been found that when the terrain is either
in a near-field regime or contains non-flat topography, the optimal trimming process is substantially more involved, so
much so that a new per-pixel SAR back-projection imaging algorithm has been developed. The new algorithm removes
incoherent energy from the SAR CCD collection pair on a per-pixel basis according to the local radar geometry and
topography, leaving a higher coherence CCD product. In order to validate the approach, change detection measurements
were conducted with GB-SAR, a ground-based indoor radar measurement facility.
Monostatic Synthetic Aperture Radar (SAR) Coherent Change Detection (CCD) has been found to be of great utility in
detecting changes that occur on the ground. Detectable changes of interest include vehicle tracks and water flow. The
CCD procedure involves performing repeat pass radar collections, to form a coherence product, where ground
disturbances can induce detectable incoherence. However there is usually a difference in the radar collection geometry
which can lead to incoherent energy noise entering the CCD, which reduces the detectability of tracks. When sensing flat
terrain, the incoherence due to collection geometry difference can be removed through a conventional Fourier image
support trimming process. However, it has been found that when the terrain contains non-flat topography, the optimal
trimming process is substantially more involved, so much so that a new per-pixel SAR back-projection imaging
algorithm has been developed. This algorithm trims off incoherent energy on a per-pixel basis according to the local
In order to validate the bistatic SAR generalization to the monostatic per-pixel formalism and algorithm, bistatic change
detection measurements were conducted with the GB-SAR system, and these are reported here.
A method of Coherent Change Detection (CCD) performance prediction is described based on (1) a simple analysis of
the frequency support overlap between the two collects which encapsulates imaging geometry effects and (2) a method
of relating environmental effects to average scatterer disturbance which can be assessed empirically. The strength of this
approach is that, once the average disturbance for a particular environmental effect has been established from one
system, it can be extrapolated to all other systems since mean disturbance is system-independent. Validation and
application of this approach using simulated examples is presented.
Measurement times for synthetic aperture radar (SAR) image collection can take from the order of seconds to minutes
and consequently the technique is subject to imaging artefacts due to target motion. For example, imaged moving targets
can be displaced and unfocussed and similarly for vibrating targets. Current understanding of this phenomenon is
somewhat esoteric however this paper puts forward and demonstrates a visual explanation via the physics of modulated
scatterer SAR images in the Fourier domain. This novel approach has led to an imagery analyst aid which associates a
distinctive signature to modulated scatterer artefacts in SAR imagery and to an associated filter.
An analysis of 3-D SAR image formation under the challenging condition of single pass sampling in the elevation
dimension is presented. The analysis is operationally relevant as it is often not possible for a radar platform to collect
radar data at sufficient grazing angles to satisfy the Nyquist sampling criterion.
It is found that these sampling issues can partly be overcome through the use of non-linear radar platform trajectories. In
conventional 2-D SAR imaging this approach can be viewed as detrimental, as the image depth of focus is reduced,
however for 3-D imaging a reduced depth of focus has been found to be advantageous.
The approach however, comes at the cost of resultant unusual image point spread functions, with coarser resolution in
the vertical dimension. It is possible to obtain a wide range of point spread functions as a function of collection
parameters including range, the form of the non-linear radar platform trajectories and centre frequency. This work
explores this parameter space to find advantageous radar collection geometries.
The image point spread functions are difficult to characterise analytically and so a numerical approach is undertaken.
Current SAR imaging techniques assume that radar pulses are reflected from a scene by a single bounce event (reflection
from a sphere), or multiple bounces producing a fixed phase-centre (a trihedral). However, scattering is often more
complex; e.g. the pulse may reflect off the ground before interacting with a vehicle, leading to additional bright returns in
the image which are not located at the position of either bounce.
In this paper we use simulation to assess the affect of multipath on vehicle signatures and develop techniques for the
identification and removal of multipath returns from SAR imagery.