Cloud Influence on Microwave Sensing of the Ocean


The usage of satellite IR (infrared) and visible techniques to study oceanographic phenomena and processes in the waters surrounding Taiwan presents serious difficulties because of cloudiness and fogs. The usage of microwave sensors, however, allows this difficulty to be overcome since cloud is a semitransparent medium for microwaves. The main factors influencing the atmospheric microwave emission and attenuation are molecular oxygen, water vapor, clouds and precipitation. Dependencies of microwave absorption due to small cloud droplets and ice particles on wavelength and temperature are given in other papers. Based on microwave measurements of atmosphere emission, the technique for estimating the total cloud absorption and the total cloud liquid water content is described. Experimental data on cloud and rain emission at wavelengths of 2.3 cm were obtained near the northern coast of Taiwan. Detailed analyses of the microwave measurements of different kinds of cloudiness and rains together with weather maps, satellite infrared images, radiosonde data and rain gauge data covering February 19 and March 19-20, 1994 are presented. These microwave measurements are used in this paper to estimate the typical spatial scales of total cloud absorption variations, a distribution of cloudiness in the total (integrated) liquid water content and the influence of winter monsoon clouds near Taiwan on ocean sensing at frequencies of the Special Sensor Microwave/Imager. The probability of heavy clouds with a total liquid water content 1 kg/m2 significantly influencing on satellite microwave sensing of the ocean, was about 2.5%.

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