The use of active and passive microwave imagery in combination is the optimum way to observe the morphology and dynamics of near shore ice. Active and passive microwave data from aircraft that are described in this paper are also compared to the ESMR (Electrically Scanning Microwave Radiometer) imagery of the Nimbus-5 satellite. The information thus obtained shows how the data to be received from the SAR (Synthetic Aperture Radar) and SMMR (Scanning Multichannel Microwave Radiometer) and on Seasat A and Nimbus G have the potential of providing a vastly increased understanding of the near shore ice of the Beaufort Sea.
The current need for sea ice information has occurred at a time of rapid-evolution of both remote sensing platforms and sensors. These timely technical advances are beginning to eliminate the observational barriers that have limited our knowledge of a natural phenomenon existing in areas that are dark and/or cloud-covered much of the year. Furthermore, since sea ice undergoes large spatial variations on short time scales, the new sensing techniques are for the first time acquiring the sequential synoptic observations needed for cause and effect studies.
Considerable emphasis has in recent years been placed on the microwave remote sensing of sea ice because it offers the possibility of an all-weather, day-or-night, capability. Both passive and active microwave remote sensing techniques have been explored. An overview of these activities has been given in Campbell et ala (1975). Early work in this area utilized passive microwave techniques since such techniques were the first to be incorporated on board earth-viewing satellites.
The most important series of aircraft flights which demonstrated the feasibility and usefulness of ice observations by means of passive microwave sensors were those that occurred during the NASAAIDJEX (Arctic Ice Dynamics Joint Experiment) joint program. A series-of three AIDJEX pilot field experiments were performed during the springs of 1970, 1971 and 1972 in the southern Beaufort Sea. During each of these experiments, the NASA CV-990 "Galileo I " performed a variety of flights ranging in altitude from 150 m to 11 km. A wide variety of visual and infrared sensors were operated in addition to an imaging radiometer operated at a wavelength of 1.55cm and fixed-beam radiometers operated at wavelengths of 0.81, 2.8, 6.0, and 2lcm.
The 1970 data (Wilheit et al, 1972) showed that it was possible to distinguish sea-ice from liquid water both through the clouds and in the dark. This finding was useful because it pointed the way to an "all-time" ability to observe leads and polynyas. These data also showed that strong microwave emissivity differences occur on the ice surface itself. However, the lack of sufficient ground truth data prevented a determination of the reason for these differences.