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