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Resolution, Polarization and Imaging |
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High-resolution images
The Ultra-Fine resolution mode, available on RADARSAT-2, acquires images at a spatial
resolution of three metres. In this mode, the radar operates with the highest sampling rate,
therefore the ground coverage is limited (10 to 30 km) to keep the acquisition within the
recording limits. The Ultra-Fine imaging mode provides the best resolution available
commercially with a spaceborne SAR system. This better detect targets
that are closely spaced and provide enhanced definition of other targets,
thereby reducing ambiguities and increasing confidence in the data.
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Ultra-Fine mode simulation image of Ottawa, Ontario, resolution of three
metres. (© CCRS. Acquired by CV-580 C-band SAR. Processed by CCRS) |
RADARSAT-1 Standard mode image, resolution of 25
metres. (© CSA. Received by CCRS. Processed and delivered by RSI) |
Data polarization
RADARSAT-1 provided horizontal-transmit and horizontal-receive (HH) data only. RADARSAT-2
can transmit horizontal (H) and vertical (V) polarizations and, depending
on the selected mode, the sensor receives either H or V signals or both of the signals
simultaneously. Therefore, in addition to providing complete RADARSAT-1 continuity,
RADARSAT-2 generates products with VV polarization, cross-polarization (HV or VH),
dual-polarization (HH+HV or VV+VH) or quad-polarization (HH+VV+HV+VH) over a range of spatial
resolutions. This allows the end-user to select the combination that is best for
the specific application.
Each scattering element (HH, VV, HV and VH) has varying sensitivities to different surface
characteristics and properties, helping to improve the discrimination between features.
Moreover, polarimetric data can be used to characterize the polarimetric signature of various
surface features, which is very useful in the study of scattering mechanisms and in
resolving ambiguities about the observed area.
HH, VV, HV and colour composite of linear polarizations images of agricultural fields in southern Manitoba (© CCRS 1993. Acquired by the CV-580 C-band SAR. Processed and provided by CCRS)
Dual-sided imaging
RADARSAT-1 has wide area coverage with its large
accessibility swath. However, the revisit time for some latitudes
can be a limiting factor in
some applications. Left- and right-looking modes on RADARSAT-2 reduce the revisit
time by one half and the accessibility swath is doubled. In effect, the market for SAR
images expands as applications that were not previously feasible will be given an
opportunity to develop. Moreover, in emergency situations, the choice of beam mode and
position can be set to ensure the greatest repeat coverage of the region of interest.
Nominally, 10 minutes are required to switch from one side to the other. The flexibility of
RADARSAT-2 makes it a powerful tool to support world mapping and disaster management
activities.
Imaging modes
Click on the image to enlarge
Beam Mode |
Approximate Incidence Angle |
Nominal Swath width |
Swath Coverage to left or right of ground track |
Approximate Resolution GND Rg x Az |
Selective Polarization transmit H or V receive H and / or V |
Fine |
36° - 48° |
50 km |
525 - 750 km |
10 x 9 m |
Standard |
20° - 49° |
100 km |
250 - 750 km |
25 x 28 m |
Low Incidence |
16.5° |
170 km |
125 - 300 km |
40 x 28 m |
High Incidence |
49° - 60° |
70 km |
750 - 1000 km |
20 x 28 m |
Wide |
20° - 45° |
150 km |
250 - 650 km |
25 x 28 m |
ScanSAR Narrow |
20° - 47° |
300 km |
250 - 600 km |
50 x 50 m |
ScanSAR Wide |
20° - 47° |
500 km |
250 - 720 km |
100 x 100 m |
Polarimetric transmit H and V on alternate pulses / receive H and V on any pulse |
Fine Quad-Pol |
30° - 41° |
25 - 50 km |
400 - 600 km |
11 x 9 m |
Standard Quad-Pol |
20° - 41° |
25 - 50 km |
250 - 600 km |
25 x 28 m |
Selective Single Polarization transmit H or V receive H or V |
Ultra-Fine Narrow |
30° - 40° |
10 km |
400 - 550 km |
3 x 3 m |
Ultra-Fine Wide |
30° - 40° |
20 km |
400 - 550 km |
3 x 3 m |
Triple Fine |
30° - 49° |
50 km |
400 - 750 km |
11 x 9 m |
Fine Beam Modes
Fine Beam modes are intended for applications which require higher spatial resolution and
lower swath coverage. Fine Resolution Beams cover the incidence angle range from 30° to 50°.
This imaging mode is available in co-polarization, cross-polarization, dual-polarization
and quad-polarization.
In addition, several new Fine Resolution products is
available on RADARSAT-2, and the list of enhanced imaging modes
follows.
Triple Fine Beam
The Triple Fine Resolution Beam mode is the three-look version of the Fine Resolution mode,
therefore providing the same spatial resolution with improved radiometric resolution.
The three looks are made possible by the higher sampling rate of the RADARSAT-2 SAR. The
Triple Fine imaging mode is available in selective single polarization (HH or VV).
Ultra-Fine Beam
Ultra-Fine Beam modes of three-metre resolution is intended for applications which require
very high spatial resolution. The Ultra-Fine Beam imaging mode
is available in
selective single polarization (HH or VV)
Standard Beam Modes
Standard Beams allow imaging over a wide range of incidence angles acquired in seven
different modes referred to as S1 to S7. The incidence angles range from 20° at the inner
edge of S1, to 49° at the outer edge of S7. Experience with RADARSAT-1 has demonstrated that
the Standard Beam Mode generates image quality characteristics which provide a good
compromise between spatial resolution, radiometric resolution and image coverage.
On RADARSAT-2 this
imaging mode is available in copolarization, cross-polarization, dual-polarization and
quad-polarization.
Extended Beam Modes
Low Incidence
An Extended Low Incidence Beam will cover the incidence angle range from 10° to 23° with
a swath coverage of 170 km. At these incidence angles, the antenna operates beyond its
optimum range, therefore some minor degradation of the image can be expected. The spatial
resolution is the same as Standard Beams. This imaging mode is available in
copolarization, cross-polarization and dual-polarization.
High Incidence
The incidence angle range beyond 49° is covered with the High Incidence Beams up to 60°.
As with the Low Incidence Beams, minor degradation of the image can be expected due the
operation of the antenna outside its optimal range. The spatial resolution is the same as
Standard Beams. This imaging mode is available in co-polarization,
cross-polarization and dual-polarization.
Wide Swath Mode
Wide Swath Beams allow the coverage of a larger region than the Standard Beam at the expense
of a slightly coarser spatial resolution. Three Wide Swath Beams cover a range on incidence
angles from 20° to 45°. This imaging mode is available in
copolarization,
cross-polarization and dual-polarization.
ScanSAR Mode
ScanSAR imagery is generated with a combination of single beams covering adjoining swaths.
This provides the largest swath coverage available in RADARSAT-2 products. However, the
increased coverage is obtained at the expense of spatial resolution. ScanSAR imaging mode
is available in copolarization, cross-polarization and dual-polarization.
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