Cloud Base Height Measurement Methods Based on Dual-camera Stereovision

A pair of digital cameras whose baseline length are 60 meters are used to constitute a binocular imaging cloud base height measurement system, which can be used in image acquisition, processing, calibration, the whole sky cloud image splicing, cloud high layer and calculation and data storage and terminal display, etc. Along with the digital camera technology and stereoscopic vision sensor development, binocular imaging visual sensor is widely used because of its simple structure, good usability and higher measuring accuracy. Through the laboratory calibration and field calibration for internal and external bearing elements, obtaining two cameras inside, outside elements and relative attitude angle, the measurement accuracy are improved. The CCD acquisition cloud image has some disadvantages such as poor texture and low signal-to-noise ratio, therefore, image enhancement and filtering pretreatment should be carried out to meet the image feature extraction and matching requirements. Through the method of histogram equalization to enhance the images, sub-pixel corner point detector are used to improve the measurement precision. The normalized cross-correlation method for regional correlation are adopted for same name point detection, which will be eliminated by introducing the polar constraint reference to image matching process.Then according to the matching feature points, getting relative parallax, height of cloud base can be calculated by use of photography measurement principle. The cameras are calibrated in lab for internal and external elements first, then calibrated using the star relative position and attitude angle of camera relationship on the spot, which ensures the measurement precision. In Beijing, with CL31 ceilometer for contrast test, concrete analysis are carried out to investigate the system error and possible causes for this cloud height measurement system.Binocular imaging cloud base high measuring methods is direct photogrammetry method, which has overcome the poor accuracy of passive remote sensing and improved the measuring accuracy. According to the analysis, the accuracy can be improved through improving camera resolution, calibrating the internal and external elements of camera, correcting relative attitude angles of the two cameras, and controlling sample synchronization time and so on.However, visible light image sensor is greatly influenced by light and obstruction, which is only suitable in a daylight and when the cloud image texture is clear. In order to reduce the influence of illumination and improve data acquisition rate, infrared image sensor can be used to constitute a binocular imaging cloud base high measuring system, to realize cloud base high measurement.