Hu Shuzhen, Ma Shuqing, Tao Fa, et al. An experiment study of all-sky cloud amount observation based on infrared real-time threshold. J Appl Meteor Sci, 2013, 24(2): 179-188.
Citation: Hu Shuzhen, Ma Shuqing, Tao Fa, et al. An experiment study of all-sky cloud amount observation based on infrared real-time threshold. J Appl Meteor Sci, 2013, 24(2): 179-188.

An Experiment Study of All-sky Cloud Amount Observation Based on Infrared Real-time Threshold

  • Received Date: 2012-06-28
  • Rev Recd Date: 2012-12-26
  • Publish Date: 2013-04-30
  • The cloud typically covers about 50% of the earth surface, affecting the energy balance, water circulation of the earth, and influencing global climate. Cloud cover and cloud base height are the primary elements in the observation of clouds, wherein the cloud amount reflects the regional weather and climate characteristics. However, the operating artificial observation method for cloud amount in China lacks objectivity and costs too much workforce. Therefore, the research and development of an automatic measuring cloud device is extremely necessary.An infrared cloud detector based on the different characteristics of visible and infrared cloud images is developed in order to measure cloud amount. The infrared sensors regularly scan the whole sky under the control of the rotating platform, and stitching all-sky images of infrared brightness temperature. Based on the different characteristics of cloud images shown in infrared, different temperature at different elevation for the cloud point and non-cloud point is considered, combining with real-time infrared brightness temperature and ground environmental parameters. The temperature threshold functions are real-time determined from the zenith to the horizontal, the all-sky cloud distribution and cloud amount are derived using the method of segmentation. This method is effective in reducing the ground environmental parameters and the sunlight on the cloud images, and it can run properly throughout the day. The cloud measuring system can provide real-time analysis of the sky condition, cloud distribution and cloud amount. The system is fully automated and adaptable for all weather conditions, with high temporal resolution and accurate observation time, and it can show the cloud trajectory of the whole period and cloudiness trends.Measurements of cloud system has been performed experimental observation in the synthesize experiment base of Meteorological Observation Center of CMA since May 2011. Through the comparative data analysis with the results of artificial observations and the visible cloud images, this measurement of cloud systems are proved to be able to provide results with high accuracy.
  • Fig. 1  A photo for the SIRIS-1

    Fig. 2  The schematic diagram of spherical projection

    Fig. 3  The cloud images of visible light and the whole sky maps of brightness temperature

    (a) the visible map at 1132 BT 7 July 2011, (b) the brightness map at 1130 BT 7 July 2011, (c) the visible map at 1802 BT 7 July 2011, (d) the brightness map at 1800 BT 7 July 2011

    Fig. 4  Relations between scan time and infrared brightness temperature

    (a) brightness temperature trends at clear sky moment, (b) cloudy brightness temperature trends at cloudy moment

    Fig. 5  Whole sky full of clouds, radiation image of brightness temperature and brightness temperature trends

    (a) the brightness map at 0300 BT 7 July 2011, (b) cloudy and sunny brightness temperature trends

    Fig. 6  Low-visibility, relations between scan time and infrared brightness temperature

    (a) the brightness map at 1010 BT 23 August 2011, (b) the brightness map at 1110 BT 23 August 2011, (c) the brightness temperature trends of Fig. 6a and Fig. 6b

    Fig. 7  Relations between infrared brightness temperature and pitch angle

    (a) the brightness temperature trend of different time under the clear sky radiations, (b) the trend of sky brightness temperature minus the ground temperature

    Fig. 8  Comparisons of artificial observed cloud amount and infrared observed cloud amount

    (a) middle and low cloud situations with high visibility, (b) middle and low cloud situations with low visibility, (c) cirrus with high visibility

    Fig. 9  The cloud amount distribution of manual observation and ground-based measurements of cloud systems

    Fig. 10  The percentage relative error of manual observation and ground-based measurements of cloud systems

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    • Received : 2012-06-28
    • Accepted : 2012-12-26
    • Published : 2013-04-30

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