BEER A 5 
RE a 
Table I - WMO Classification Scheme 
  
  
  
Class Thickness Description Symbol 
(cm) 
Frazil 0-5 Fine spicules or plates suspended in water Z 
Grease 0-5 Crystals coagulated to form a soupy layer RI 
on surface Ei 
zi 
Dark Nilas 5 Thin elastic crust of black ice ND 
Light Nilas 5-10 As above, thicker, with some lighter NL 
appearance 
< 
Grey 10-15 Thicker, grey in appearance e: IS 
Grey-white 15-30 Thicker, light-grey in appearance L z 
First-year 30-200 Thick, white, in first year of growth, saline FY 
Second-year 200 Thick, less saline, strong, in second-year sys 
of growth Ë 
Multi-year 200 As above, in at least third year of growth MY 
  
Active sensors also have been used to study sea ice leading back to 
1969 when Rouse used a VV-polarized Ku-band scatterometer to distinguish rough 
and smooth FY ice and MY ice and open water. Parashar et al. (1974), used 
backscatter UHF and Ku-band frequencies to stuly ice classification. Gray 
et al. (1977a, b) showed that substantial variability occurs in the radar cross 
section of the same ice classes which can make interpretation of radar response 
less clear than might be anticipated from earlier work. The most complete 
frequency analysis of the radar cross section of sea ice to our knowledge has 
been done by Onstott and co-workers at the University of Kansas, Onstott et al. 
(1979, 1981, 1982). This work will be further discussed below. 
  
  
Work at the Canada Centre for Remote Sensing (CCRS) has highlighted the 
benefits of simultaneous active and passive measurements beginning with a study 
as part of the Canadian SURSAT Project in 1979 and reported by Livingstone 
et al., 1982. This data set consisted of mainly cold winter ice conditions, but 
subsequent work attempted to follow the seasonal variation of the microwave 
properties. 
The principal sensors used by CCRS include a Ku-band, dual-polarized 
scatterometer; a K-band, H-polarized radiometer; a PRT5 infrared radiometer; and 
a multi-frequency, dual-polarized synthetic aperture radar (SAR). 
2.0 Seasonal Variation of Microwave Signatures 
  
Many of the results from our work on the seasonal variations of 
microwave signatures have been reported in Hawkins et al. (1981) and Gray et al. 
(1982). These results will be briefly summarized in this section. 
  
790