3.0 Choice of Fundamental Radar Parameters for Detection and 
Identification of Sea Ice 
  
In this section, we discuss the influence of the choice of four 
fundamental radar parameters (frequency, incidence angle, polarization and 
resolution) on the effectiveness of the radar for sea-ice reconnaissance. 
3.1 Frequency 
The most extensive study of the frequency behaviour of radar cross 
section for sea ice has been done by workers at the University of Kansas 
(Onstott et al., 1979, 1981, 1982) who have facilities to do a calibrated scan 
at discrete frequencies on the same ice. Other workers are often restricted to 
a single frequency or uncalibrated imagery. For cold winter conditions, Onstott 
has reported considerable variation in radar contrast with frequency between FY 
and MY ice, with neglible contrast at L-band and contrasts of approximately 
10 dB for frequencies of X-band or greater. 
  
Until recently the band of frequencies between L and X-band has been 
largely unexplored. Preliminary new results reported by Onstott et al. (1982b), 
show that under the conditions which prevailed near Mould Bay, N.W.T., in 
October, 1981, radar contrasts between MY and FY are ^5 dB at 4 GHz and 
increase to ~10 dB at 16 GHz with the absolute value increasing steadily with 
frequency having -15 dB variation over the frequency range. Figure 4 shows a 
comparison of simultaneous SAR imagery taken later in the same season in the 
Beaufort Sea. In each case, X-band data are compared to C-band and L-band in 
steep geometry. These examples demonstrate that indeed the radiometric contrast 
between ice classes is greatest at X-band and lowest at L-band with C-band being 
in a intermediate position consistent with Onstott's results later in this 
season. Although the conclusion is based on imagery which is seriously degraded 
due to limitations in the C-band channel, it is believed to be a general result, 
at least in the ice conditions studied. 
3.2 Incidence angle 
The incidence angle dependence of o © over the range from nadir to 60° 
has been well studied using scatterometer techniques (Gray et al., Parashar, 
1973, Onstott, 1979a,b). Figure 3 shows this behaviour over three seasons 
for Beaufort Sea ice. From these curves there seems to be a slight advantage in 
radar contrast between FY and MY at the larger incidence angles, but greater 
benefit is derived when the ice-water contrast is considerel. A choice of 
incidence angle greater than 35° would allow sufficient contrast at Ku band to 
separate MY from open ocean even at windspeeds of 20 m/s* and most ice types 
from open water at more moderate winlspeeds. 
Much of the variability of radar cross section for the same ice class 
can be attributed to associated changes of local scene roughness (for example 
frost flowers on young ice). Scene roughness, however, couples together both 
792 
a = » 
= ee er pa i ee - A 
ne ee LU ER 
| 
st 
cc 
st 
<A