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Title
Proceedings of the Symposium on Global and Environmental Monitoring

77
al, 1989; and Cihlar et al, 1990), geological
feature mapping, and backscatter
characteristics of forestry targets (Wehrle,
1989) .
SAR SYSTEM DESCRIPTION
The new generation airborne synthetic aperture
radar (SAR) is a dual frequency C-Band/ X-
Band, dual polarized system that transmits
either H or V polarization and receives both
polarizations simultaneously (Livingstone et
al, 1988). It is fully digitally-controlled,
with digital motion compensation across the
swath and dynamic antenna stabilization. It
also features an onboard 7-look real-time
processor and display, and data imaging in one
of three selectable operating modes, nadir,
narrow or wide. In the nadir and narrow modes,
swaths of 22 km and 18 km are imaged from the
optimum aircraft altitude of 6 km, with high
resolution of 6 m in azimuth and range. Lower
resolution (20 m x 10 m) imagery can be
obtained over a wide swath of about 63 km, for
maximum ground coverage. In all cases, 4096
range pixels are processed across the swath.
The system incorporates a high power
transmitter, with a low power transmitter as
back-up.
In-flight outputs from the SAR include high
density digital tapes of signal data and image
data processed ana recorded in-flight, hard
copy print and video display of imagery
produced in real-time for quick review, and
digital data tapes of navigation parameters.
On the ground, the high density image tapes
are transcribed to computer compatible format
(CCT), and high quality imagery can be
generated in strip form as positive or
negative print. The signal tapes can be
processed to 16-bit image CCTs, using the C-
SHARP system in operation at OCRS.
RADAR SENSOR DEVELOPMENTS
New radar sensor developments at OCRS are
underway to utilize the phase of the SAR
signal. These developments include
interferometric SAR, a new SAR mode with the
potential of providing terrain elevation
information to better than 10 m rms (Cumming
et al, 1990), and polarimetric SAR
(Livingstone et al, 1990), to provide enhanced
target classification. As well there are
upgrades to the airborne system and precision
ground processor, to provide an end-to-end
capability for data acquisition and processing
of phase coherent data. In addition, there
have been continuing calibration developments
that have increased understanding and ability
in radiometric calibration (Lukowski et al,
1990) , to allow more accurate derivation of
target signature and intercomparison of multi-
temporal data sets.
Polarimetric SAR
In the past, remote sensing radar applications
have required and relied on good image
radiometry, but recent research work in the
application of image phase has indicated the
potential of radar phase information.
Polarimetric SAR with phase and amplitude
information provides additional target scene
parameters and offers the possibility of use
as a standard quantitative remote sensing
tool, for example in forestry and agriculture
classification.
CCRS, together with the Defence Research
Establishment Ottawa, initiated a project in
1988 to develop a polarimetric SAR capability.
The project has involved design and
implementation of hardware modifications to
the airborne system, and development of
software and a PC-based workstation for data
processing, analysis and display. Following a
study of the feasibility and design of using
the CCRS SAR in a polarimetric mode, a simple
experimental X-Band polarimeter was
implemented. This configuration makes use of
a single junction ferrite switching circulator
to multiplex H and V polarized pulses. With
the radar transmitter running at twice its
normal pulse repetition frequency, the
returned signals are processed by a single
receiver. The signal recording interface
allows a full polarimetric data set to be
recorded. These recorded signal data are
stripped and processed to four spatially
registered complex images which are then
corrected for system gain artifacts and cross
channel leakages prior to the polarization
synthesis. The first flights were carried out
in August 1988 over urban and rural test sites
in Ottawa and Petawawa, and data was used to
demonstrate the polarimeter function and to
test the workstation. Following further
successful airborne acquisition with this
prototype X-Band polarimeter, a triple
junction ferrite switching circulator was
designed and built by ComDev Ltd. to CCRS
specification for C-Band frequency, the
preferred frequency for polarimetric research.
This new switch is designed to have lower
cross-channel leakages, and is thermally
regulated, to provide higher performance and
calibration accuracy. Integration of the C-
Band switch into the system is planned for
early winter, 1990. Analysis of the X-Band
polarimetric data sets has already indicated
their potential for enhanced target and
terrain differentiation; use of the new C-Band
mode should provide excellent data sets for
polarimetric application studies.
Interferometric SAR, InSAR
CCRS is developing an interferometric SAR
capability, InSAR, as an additional
operational mode of the airborne C-Band SAR.
By using the conventional SAR for transmitting
and receiving the radar signal, and adding a
second antenna and receiving channel, another
registered image with a small cross-track
parallax is obtained. When the two received
channels are processed, interferometric phase
patterns are obtained that are modulated by
the height variations in the imaged terrain.
The phase patterns are then analyzed to obtain
the elevation of each pixel in the scene. The
resulting digital elevation model should be
more accurate than those available from stereo
SAR requiring two passes of airborne SAR data
which have errors from pass registration and
image correlation. From studies of the
interferometric process and the sources of
error, the modification of the C-Band SAR
should lead to relative elevation accuracies
of better than 10 m rms, which promise to be
of great interest for many survey and mapping
applications.
Based on the results of these analyses, and
preliminary test data, the modification of the
airborne system is underway. A second C-Band
antenna has been completed and characterized,
and is to be installed on the side of the
Convair-580 fuselage in the winter of 1990.
The ground processor has been developed and
will provide differential motion compensation