The earth sensing community is poised to exploit more and more heavily a frequency allocation around 9.6 GHz which they employ for high-power (1-5 kW) space-borne downward-pointing synthetic aperture radars. These vehicles are noted as the SARn series, of which SAR1 has been operating since 1995 --
http://www.space.gc.ca/asc/eng/satellites/radarsat1/default.asp
and the next launch, of a more powerful vehicle, is currently slated for 2007 February, see http://news.eoportal.org/eomissions/061127_terrax.html
The table shown below gives typical operating parameters for these SARs. Note that the average power is about an order of magnitude lower than the peak. More recent and future proposed systems (of which there are several) will have higher bandwidths because the ITU is poised to approve an expansion of the 9.6 GHz allocation by an additional contiguous 200 MHz (its Agenda Item 1.3 of WRC07); future 9.6 GHz SAR will radiate nearer to the radio astronomy protected band at 10.6 GHz.
The possible ill effects of the SARn instruments upon radio astronomy should be readily apparent; in a main-beam encounter, most of the energy incident on an antenna (typically a large fraction of a Watt) also lands on the receiving device. The situation is in fact probably more complicated than with CloudSat (http://www.iucaf.org/CloudSat/), a similarly powered satellite working at 94.05 GHz, because the 9.6 GHz devices are not purely downward-pointing. The following table has been taken from an ITU document (actually, 8B/39 of the current cycle, preceding WRC07) used for generic compatibility studies between SARn missions and nearby (in frequency) radiolocation (i.e. radar) services.
Parameter |
SAR1 |
SAR2 |
SAR3 |
Orbital altitude |
400
km |
619
km |
506
km |
Orbital inclination |
57˚ |
98˚
|
98˚
|
RF centre frequency |
9.6
GHz |
9.6
GHz |
9.6
GHz |
Peak radiated power |
1
500 W |
5
000 W |
5
000 W |
Pulse modulation |
Linear
FM chirp |
Linear
FM chirp |
Linear
FM chirp |
Pulse bandwidth |
10
MHz |
400
MHz |
450
MHz |
Pulse duration |
33.8
ms |
10-100
ms |
1-10
ms |
Pulse repetition rate |
1
736 pps |
2
000-5 000 pps |
410-515
pps |
Duty cycle |
5.9% |
2.0-40.0% |
0.04-0.5% |
Range
compression ratio |
338 |
<12
000 |
450 |
Antenna type |
Slotted
waveguide |
Planar
array |
Planar
Phased Array |
Antenna peak gain |
44.0
dBi |
~46.0
dBi |
54.5-57.5
dBi |
Antenna orientation |
20˚
to 55˚ from |
34˚
from |
20˚
to 44˚ from Nadir |
Antenna beamwidth |
5.5˚
(El) |
1.6-2.3˚
(El) |
1.1-2.3˚
(El) |
Antenna polarization |
Linear
vertical |
Linear
HH or VV |
Linear
|
System
noise temperature |
551 K |
~500
K |
600
K |
Afterword:
Radio astronomy has been operating for several years in the presence of EESS missions
which focus high-power radar beams on the earth for global imaging; not only
RadarSat1 noted above, but others like envisat which operates at Ku and C-band
(http://envisat.esa.int/instruments/ra2/)
and more recently, CloudSat (www.iucaf.org/CloudSat/)
at 94 GHz. As new astronomy systems are
rolled out which grant increased access to unprotected portions of the
spectrum, new hazards will be encountered.
Allocations for earth-exploration systems like those discussed here can
be found in the Radio Regulations in a very large number of bands, namely (in
GHz) 0.432-0.438, 1.215-1.240,
1.240-1.300, 3.100-3.300,5.250-5.255, 5.255-5.350, 5.350-5.460, 5.470-5.570,
8.550-8.650, 9.500-9.800, 13.250-13.400, 13.400-13.750, 17.200-17.300, 24.050-24.250,
35.500-3.600, 94.000-94.100 and 130-134 GHz.
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