Full text: Mesures physiques et signatures en télédétection

H. Otti and K.H. Zeller 
DLR, German Aerospace Research Establishment 
Institute of Radio Frequency Technology 
82234 Oberpfaffenhofen, Germany 
Tel.: +49-8153-28-2365, FAX: +49-8153-28-1449 
For more than 10 years spaceborne SAR systems have been considered as indispensable sensors in 
the scenario of EOS. 
Unfortunately, due to funding problems, the EOS programme has been delayed. Further 
more, the idea of large multisensor-platforms has been dropped in favour of smaller units carrying 
only a few sensors, which also eases the problem of data links. 
Discussions held at JPL in January 1993 were focussed on international cooperation con 
cerning the use of SAR satellites and the adoption of mission goads. It was emphasized that ESA 
continues with C-band SAR sensors on board ENVISAT as does Canada with RADARSAT in the 
same frequency band. 
Japan is expected to keep L-band in future JERS type satellites, while NASA is planning a 
polarimetric L-band SAR satellite which would carry an X-band sensor provided by Germany and 
eventually other European countries. 
The purpose of the paper is to outline the main characteristics of the envisaged X-band 
sensor, based on modern technology and an active phased array concept. Emphasis is being put on 
a good efficiency at the conversion from DC into radiated RF power, and vice versa on low losses 
between the antenna surface and low noise amplifiers, in order to achieve a low noise figure and to 
keep the demand on satellite power low. The required technology is presently under study within 
the German and Swedish electronic and space industry. Potential solutions will be indicated. 
The required sensitivity (noise floor) of the system with respect to land applications will 
be discussed as well as electronic beam steering (off-nadir angle range) and the achievable revisit 
cycle for a specific near polar orbit altitude. The studied X-band SAR allows principally polarimet 
ric measurements, but satellite power constrains those measurements (for the backscattered cross 
polarized signals) to certain off-nadir angle ranges only. Therefore, the baseline is dual polariza 
tion. The operational modes of the X-band SAR will include high resolution capability. However, 
the L-band SAR of NASA/JPL will most likely be a fully polarimetric system optimized for wide 
swath coverage and medium resolution, (of course with the possibility to change the operational 
modes). The combination of a polarimetric L-band SAR and a dual polarized X-band SAR, both 
with variable modes (SCANSAR, SPOTLIGHT), is a promising idea for global observations from 

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