Application of brightness temperature data from a ground-based microwave radiometer to issue low-level windshear alert over Hong Kong International Airport

The use of the microwave radiometer in the alerting of low-level windshear at the Hong Kong International Airport has been discussed in Chan and Lee (2011). This paper extends the previous work by considering all the 14 channels of the microwave radiometer in use in Hong Kong and trying out other proxies of the fluctuations of the brightness temperature of the radiometer apart from variance, namely, auto-correlation of the time series. It turns out that the oxygen channels with frequencies in the region of 57 to 58 GHz perform the best in the capturing of the low-level windshear, probably because their effective ranges are close to the heights of the windshear reports (below 500 m, or 1600 feet) and there are temperature fluctuations associated with terrain-induced windshear, the main cause of low-level windshear in the spring time (the period under investigation in this study). By combining the radiometer-based windshear alerts with those from the Light Detection And Ranging (LIDAR) systems or the Windshear and Turbulence Warning System (WTWS), it is possible to achieve a hit rate of pilot windshear reports close to 95% and an alert duration less than 20% over the most used departure runway corridor in the spring time, which are comparable with the overall windshear alerting service at the Hong Kong airport. Among the two approaches, viz., (i) variance and (ii) auto correlation coefficient of the brightness temperatures, the variance of brightness temperature of the radiometer performs slightly better with a higher hit rate.