Commercial interest is largely due to prediction of drift ice
location and movement for hazard alleviation with ship routing
and oil exploration. Also of interest is the location of
fronts advantageous for fishing.
The research community is interested in ice characteri-
stics such as roughness, types (new, first year and multi-year
ice), snow cover (thickness extent and accumulation rates) and
ice thickness (surface and subsurface).
Interest in ship monitoring is related to the control of
national fishing stocks, to the detection of fleets or indivi-
dual ships fishing illegally and to safe ship navigation in
arctic seas.
4.2 A GUIDELINE FOR SYSTEM DESIGN
Around the initial concept of a dual look system a number
of alternative configurations can be conceived. Two possible
implementations have been analyzed during the study: (i) subse-
quent processing steps, with different characteristics, of the
same data provided by a single SAR, (ii) multimode operations
of a composite SAR system having at least a high resolution
and narrow swath mode and a mode with low resolution, wide
swath capabilities.
In the case (i), a high resolution wide swath SAR is con-
sidered in which the first look at low resolution is obtained
by low pass filtering the raw data, while the high resolution
second look is achieved by taking the raw signals at their own
data rate. In another embodiment, the system may sense the
environment with different frequencies and polarizations. Re-
gardless the spatial resolution, the lst look mode is imple-
mented by processing a limited number of channels (i.e. fre-
quency and/or polarization) among those available. In the 2nd
look mode, the data provided by the bulk of channels are pro-
cessed for a narrow swath. The approach outlined has the ad-
vantage of requiring just one SAR even if equipped with high
prime power. The disadvantages are related to limited flexibi-
lity of the system and the high data throughput required. The-
se remarks motivate the scarse interest on this system solu-
tion.
System (ii) is preferred as it is more flexible even
though it requires a SAR with multimode operation capability
or separate SAR sensors. Let us consider the basic dual modes
SAR: (a) low resolution wide swath (LRWS) referred to as lst
look, and (b) high resolution narrow swath (HRNS) referred to
as 2nd look. The remote sensing geometry of the dual mode SAR
is shown in Fig. 2. Two independent beams are generated. The
wide swath beam is squinted forward with respect to the satel-
lite in order to have a longer processing time to be used for
pointing the spot beam in a selected narrow area. A same pha-
sed array antenna generates the two beams by means of two se-
parate beam forming networks (BFN). The BFN of the LRWS mode
generates a fixed beam while the BFN of HRNS mode provides, by
electronic steering, an agile beam. In the along-track the
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