Ground-based Infrared Measurements Of Cloud Systems And Applications Research

Clouds affect the energy balance of the earth by means of absorbing, scatteringand radiation, and it has influences on global climate. Precipitation of clouds is themost familiar way for the earth water circulation. In the macroscopic parameters ofclouds, cloud cover and cloud base height are the primary elements in the observationof clouds. Wherein the cloud amount reflects the regional weather and climatecharacteristics, the cloud base height condition determines cloud classification andprecipitation probability. However, artificial visual is the main method used in cloudsobservation in China at present; the visual observation has more subjectivity and wastea mass of work force. Therefore, the research and development of an automaticmeasuring cloud device is extremely necessary.In this paper, an infrared cloud detector which is based on the differentcharacteristics of cloud images show in visible and infrared is developed in order tomeasure cloud base height and cloud amount.A ground-based measurement of cloud system consists of an infrared temperaturemeasuring sensor and a double location digital cloud system. The double locationdigital cloud system calculates the cloud height of zenith by photogrammetry at regulartime, and the infrared temperature measuring sensor acquires brightness temperature ofatmospheric radiation in real time. The height of clouds is deriver and tested by thedouble location digital cloud system, Combination with real-time observation of zenithsingle-point infrared brightness temperature and ground environmental parameters.The influence of sub cloud air from ground to clouds bottom to infrared brightnesstemperature is analyzed, find the feasibility of cloud base height remote sensing byground-based sky infrared brightness temperature. The result of experiments showsthat for low and middle clouds, the sky radiation brightness temperature ofground-based observation is relatively sensitive to the variation of cloud base height,therefore it can be used to the estimate cloud base height.In this paper, On the basis of decrease principle of tropospheric vertical temperature, the temperature decreasing gradient parameter K from cloud base to theground is defined and according to the decreasing gradient parameter inverse the cloudheight of zenith direction. The algorithm does not depend on the air sounding data; getthe formula of the cloud base height.The infrared sensors regularly scan the whole sky under the control of the rotatingplatform, and stitching all-sky images of infrared brightness temperature. Based on thedifferent characteristics of cloud images show in infrared, consider the differenttemperature at the different elevation about the cloud point and non-cloud point,Combination with real-time observation of all-sky infrared brightness temperature andground environmental parameters. Real-time fitting the temperature thresholdfunctions from the zenith to the horizontal, use the method of segmentation get theall-sky cloud distribution and cloud amount. This method is effective in reducing theground environmental parameters and the sun light on the cloud images, can run in realtime throughout all the day.Dual-band measurements of cloud system has been performed experimentalobservation in the synthesize experiment base of meteorological observation centre ofCMA (China meteorological administration) since July,2010, and acquires a cloudheight data of the zenith at each minute. Through the comparative data analysis withVaisala CL31, Ground-based dual-band measurements of cloud system can providecloud base height with high accuracy. About the cloud amount, through the comparativedata analysis with the results of artificial observations and the visible cloud images, thismeasurement of cloud systems can provide results with high accuracy.