Aircraft Microwave Measurements of the Arctic Ice Pack

Microwave radiometer data (19.3 GHz or 1.6 cm) taken from an aircraft mission over the Arctic Ocean near Point Barrow, Alaska, are examined. The microwave brightness temperatures corresponding to varying ice pack conditions are correlated with simultaneous photography and infrared radiation data. Microwave measurements of the surface taken both through and from beneath a stratus cloudcover are investigated for atmospheric attenuation and emission effects. The influence of clouds is greatest when viewing surfaces such as water, which appears cold at microwave frequencies because of its low emissivity. In general, cloudiness diminishes the capability of the 19.3-GHz radiometer to discriminate between ice and water. Polynya and other openings in the ice pack display a characteristic brightness temperature near 100 degrees K when viewed through a cloud-free atmosphere, whereas they appear as much as 20-40 degrees K warmer when clouds intervene between the surface and the radiometer.