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Satellites: Many Uses in War and in Disaster Prevention

Satellites: Many Uses in War and in Disaster Prevention

Excerpted from the writing of Major Cadet Chu Chiung-kuang, Department of Applied Physics, College of Science and Engineering, National Defense University
Meteorological observation is the first step in weather forecasting, and is the most direct method of keeping track of atmospheric changes. Among the methods used to record changes in meteorological factors at discrete points, along lines, or even throughout whole planes, are manual and automated observation, weather balloons, aircraft, ships, radar, and satellite sensors.
Because it is located in a subtropical zone, Taiwan is affected during the summer months by the high-pressure systems that form over the Pacific Ocean and bring southern monsoon winds and typhoons. Severe weather conditions pose great threats to human life and property in Taiwan, and may cause major natural disasters such as floods and mudslides. Because weather conditions frequently cause great inconvenience in everyday life, aviation, and military exercises, Taiwan has an urgent need for accurate water vapor forecasts.
Thanks to the rapid development of satellite technology in recent years scientists can now conveniently use information from global meteorological monitoring stations to establish relationships with brightness temperature data from channels scanned by weather satellites. This approach has yielded excellent results.
Weather satellite data is currently used to determine atmospheric water vapor via inverse analysis. While inverse analysis can be used with near-infrared, infrared, and microwave channels, the former two channels can be blocked by heavy cloud cover. Because of the short wavelength of infrared radiation (0.8-100 痠), it cannot penetrate clouds. When there is cloud cover, even though infrared radiation below the clouds is high, the distance to a satellite is too great, and the radiation will be absorbed before it can reach the satellite. In this case, it is only possible to make measurements of the water vapor in the upper and middle layers of the atmosphere. The relatively long wavelength of microwave radiation makes it less subject to interference from clouds. Even when the sky is totally overcast, microwaves emitted below the clouds can penetrate the cloud cover and reach a satellite's radiometer. As a consequence, microwave sensors can measure water vapor throughout the whole atmosphere at all times of the day and under all meteorological conditions. Microwave data from weather satellites used in conjunction with airborne data is therefore an indispensable tool in the study of atmospheric water vapor.
The use of inverse analysis of satellite and sounding data (see figures at right) is the simplest method of observing and tracking weather systems from the sea, and determining any changes. Apart from effectively increasing the temporal and spatial resolution of meteorological observation, this approach can be used to monitor the development of marine water vapor masses and gauge their strength. An effective understanding of the thermodynamic mechanisms of the atmospheric environment will enhance our ability to forecast severe weather conditions and provide information needed to prevent and alleviate natural disasters and facilitate military operations.