(4) Incidence angle: Preferably variable from 12° to 50°; also 

 nadir. 



(5) Orbit: Again a choice must be made. For estaurine and surface 

 wave studies, and investigations of small-scale current features, 

 the orbit should provide maximum coverage in coastal regions. 

 Preferably, coverage of any area should be every 6 hours, but 

 every 12 is acceptable. The temporal coverage should be on the 

 order of 10 minutes. On the other hand, for wind structure, 

 fronts and internal wave studies, the orbit should provide global 

 coverage — not sun-synchronous — so that the same spot is not 

 always observed at the same time. 



H. COMPLEMENTARY SENSORS 



The utility of SAR will be greatly enhanced if certain complementary 

 sensors are available. Most useful will be an altimeter (ALT) on board the 

 same satellite. There appears to be no need to mount a separate altimeter — a 

 separate downward looking antenna is required with the same power supply and 

 using certain electronic components common to SAR. A hybrid SAR/ALT system 

 could be designed to incorporate the requirements for both altimetry and ocean 

 surface imagery. A cost-benefit evaluation of such a system appears 

 desirable. 



A scatterometer on board the same satellite will enhance and extend the 

 capability of measuring wind speeds over the ocean. It should operate at a 

 different frequency from SAR and have a larger swath. Note also that a 

 calibrated SAR can be operated in a real aperture mode precisely as a 

 scatterometer . 



Of lower priority are visible and infrared sensors. Information of this 

 kind can be obtained from other satellites — a resolution of 1 km is acceptable 

 but finer resolution is desirable. 



I. UNRESOLVED QUESTIONS 



(1) Can the hydrodynamic and electromagnetic effects of current 

 gradients be adequately understood to allow quantitative 

 measurement of these gradients by SAR? 



(2) Can the SAR Doppler be used to detect ocean currents with a 

 spatial resolution greater than 5 km, a temporal resolution 

 greater than one day, with current velocities of 5-10 cm? 



(3) Can SAR be unambiguously related to currents — can wind and wave 

 signals be 'removed'? 



(4) Is a line-of-f light Doppler sufficient or is a new design at a 

 variable beam direction required? 



4-6 



