scattering while cross-polarized return is mainly due to the
volume scattering.
Another sensor parameter to be defined in relation to the
application is the swath width which is of the order of 100 -
200 Km for the low resolution mode and 10 - 30 Km for the high
resolution mode. The narrow swath has to be selectable within
the wide swath by means of beam steering and/or beam forming
techniques. Incidence and squint angles are additional parame-
ters defining the geometry of the remote sensing system. The
relative squint angles of the lst look beam with respect to
the beam of the 2nd look determine the amount of time avai-
lable to process, on a real time basis, the data of the 1st
look and then to select the area of interest to be imaged with
the 2nd look mode.
Another parameter related to the response time of the
system is the time interval between the successive overpasses.
It ranges from few days for land application, to a day for ice/
ocean monitoring and to few hours for ship/ocean application.
The latter requirement may require more than one satellite to
be fulfilled.
Table 1 summarizes the sensor requirements for the three
different applications and, where possible, for the st and
2nd look modes. According to these requirements a preliminary
calculation of the SAR parameters has been made for the two
modes and the three operating frequencies. The results are
summarized in Tables 2 and 3 for the LRWS and HRNS modes, re-
spectively.
4.3 SYSTEM OPTIONS GENERATION AND PRUNING
Several options derive from the different algorithms to
obtain the high resolution and low resolution images (range -
azimuth correlation function) and from the different algo-
rithms to switch between the lst and 2nd mode (i.e. SKBS) and
to understand the image information content. Another source of
system options is the technology (i.e. device and computer) to
implement the system. As a consequence, an expanding tree of
system options can be drawn representing all the possible al-
ternatives to the remote sensing problem. A major objective of
the feasibility study is represented by these options and as-
sessment of their technical feasibility, technical risk, time
required to implement, industrial fall out and cost. In order
to exploit at best the limited research effort, the majority
of options will be pruned leaving few actractive alternatives
to be analyzed more deeply, designed and tested during the 4
years study.
4.4 CRITICAL TECHNIQUES AND TECHNOLOGIES
Crucial to the system options generation is the identifi-
cation of algorithms for the pixel extraction (range - azimuth
raw data compression) and image understanding. The state of
work concerning these topics is briefly mentioned in the en-
suing subsections 4.4.1 and 4.4.2.
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