Reprint 890 Application of a Ground-based Microwave Radiometer in Cloud Observations

The use of cloud-base height data obtained from a groundbased microwave radiometer in the estimation of total cloud amount has been studied by Chan and Li (2009). The present paper extends the study by considering the performance of the total cloud amount estimation algorithm in different seasons and different years. It is found that the algorithm works generally well in different periods by comparison with the human observations of the cloud amount at the Hong Kong International Airport (HKIA). The major challenge to the methodology is the occurrence of isolated cumuli in the summer time, especially those developing over the mountains nearby HKIA. It is because such cumuli may just stay nearby the mountains and are outside the observation region of the radiometer, which is basically the column of the troposphere right above the instrument. The radiometer has also been equipped with an azimuthal positioner to make observations in different directions. As a result, a 2D map of integrated water vapour (IWV) is obtained every hour. This IWV map shows the potential of making cloud observations over nearly the whole sky dome, which is an improvement over the conventional zenith observation of the radiometer in terms of the sampling volume. Some examples of the observations of cloud movement and clearance from the 2D IWV maps would be presented in the paper.