52* 



5^^ 



50" 



49' 



48* 



47" 



46* 



43" 



42' 



41" 



Figure F-3. Superimposition of the ocean features detected by NESDIS (solid line) on 25- 

 26 April 1985 (see inset, Figure F-1) and features detected by IIP SLAR (dashed line) on 

 28 April 1985, some of which are visible in Figure F-2. 



backscatter respectively. The 

 imagery frequently shows very 

 sharply delineated fronts in great 

 detail. 



Previous work using SLAR and 

 satellite infrared in the Grand 

 Banks area was done by 

 LaViolette (1983), using an earlier 

 Coast Guard SLAR and a NASA 

 SLAR. The earlier SLAR's had 

 lower power outputs and the 

 images reproduced by LaViolette 

 are apparently less sharp and less 

 detailed than the ones produced 

 by the present model, a Motorola 

 AN/APS-1 35 Side-Looking 

 Airtx)me Multi-Mission Radar 

 (SLAM MR). 



The most extensive body of work 

 involving detection of ocean 

 features with an active microwave 

 system has been done with 

 SEASAT synthetic aperture radar 

 (SAR) (Beal, etal, 1981). Some 

 of the work done with SEASAT 

 imagery has included comparison 

 with satellite infrared imagery (Fu 

 and Holt, 1982, 1983; Hayes, 

 1981). 



Although the precise mechanism 

 is uncertain, it is clear that the 

 difference in backscatter is due to 

 a difference in surface 

 roughness. Visual inspection of 

 the sea surface during IIP flights 

 has shown that the dark and light 

 areas on the SLAR film 

 correspond closely to rough and 

 smooth areas visible under 

 conditions of light wind. Also, the 

 SLAR films contain many images 

 of intemal wave trains, many of 

 them closely linked to the 

 bathymetry of the edge of the 

 continental shelf. The alternate 

 rough and smooth bands of 

 intemal waves detected by 

 SEASAT SAR have been 

 described in Alpers and Salusti 

 (1983) and Hughes and Gower 

 (1983), among others. 



Discussions of the mechanism of 

 detecting ocean features in radar 

 imagery usually invoke Bragg 

 scattering (Valenzuela, 1978; 

 Brown, Elachi and Thompson, 

 1976), which defines a critk^l 

 surface wavelength for maximum 

 backscatter. FortheX-band 



SLAR and the range of incidence 

 angles encountered in IIP 

 operations, the range of ocean 

 wavelengths causing Bragg 

 scattering is approximatley 2-30 

 cm. The relationship between 

 the rough and snnooth patches 

 seen visually and the SLAR 

 imagery reflects the relative 

 spectral energy density in those 

 patches, (i.e., the wave height at 

 the Bragg wavelength). 



Results 



IIP SLAR imagery of ocean fronts 

 has frequently been confirmed by 

 the interpretations of Advanced 

 Very High Resolution Radiometry 

 (AVHRR) imagery by NOAA's 

 National Environmental Satellite, 

 Data and Information Service 

 (NESDIS). A simplified 

 reproduction of the NESDIS chart 

 for 26 April 1 985 is seen in Figure 

 F-1 , with an inset showing the 

 interpreter's worksheet for the 

 area outlined on the main chart. 

 Figure F-2 is a SLAR image from 

 28 April, from 

 the area outlined in Figures F-1 



87 



