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Detailed Overview of Radar Based Hail Detection System
Although severe hailstones are rare the damage associated with them can result in great economic loss especially in the agriculture industry. Precisely detecting hail from ground weather stations is difficult because of its spatial and temporal variability. The ideal alternative is to use information from weather radars to predict hail occurrence. This method uses algorithms to detect the development of hail. There are several algorithms available that are used for this purpose. To detect hail and distinguish between hail and rain meteorologists use two main techniques single-polarization radar or dual-polarization radar.
The Dual-polarization radar technique is touted as the most effective method to detect and distinguish hail today. This technique can make a precise distinction between spherical stones and non-spherical rain droplets. The Dual-polarization radar technique is also capable of measuring the ratio between horizontal and vertical polarization which helps to differentiate between rainfall and hailstone where rain always has positive deferential reflectivity. Despite its effectiveness, the dual-polarization radar technique remains underutilized and most weather stations use single-polarization radars. Most meteorological institutes use single-polarization radars information together with data from other sources to detect and distinguish hail.
There are several algorithms meteorologists use to distinguish between rain and hail where each method is unique and its effectiveness varies from one method to the other. The most common ones are the constant altitude plan position indicator (CAPPI), maximum reflectivity, the Auer method, NEXRAD method, vertical integrated liquid water (VIL) method, VIL-density, and regression equations. All these methods detect and estimate the presence and size of hail using the single-polarization radar technique. This is perhaps the main reason meteorologist institutes are still stuck with this technique today despite the presence of relatively advanced and efficient dual-polarization radar techniques.
The application of the methods stated above varies where some are used to detect hail while others are good at estimating hail size. It is worth noting that the methods of hail detection are more precise and successful compared to those of estimating hail size. Generally, most hail detection methods use upper air soundings temperature information, calibrated infrared measurements, or numerical weather predictions to estimate the presence of hails. Among the mentioned hail detection methods, the NEXRAD algorithm is established as the most reliable in detecting hail compared to other methods but the Auer method also looks promising in this field and a good number of meteorological institutes have started utilizing it. Although it is challenging identifying and detect the threshold, weather stations use the vertically integrated liquid to give hail alerts to the public. It is worth noting the effectiveness and efficiency of the hail detection method can differ significantly because of the variability in the radar system used. Therefore, it is possible to establish some differences regarding the efficiency of hail detection where a similar hail detection method is applied. Furthermore, the effectiveness and precision capability of the hail detection method will be influenced significantly by the knowledge and experience of the individuals monitoring, analyzing, and interpreting the meteorological information gathered by the hail radar system. Therefore, to successfully detect hails the ideal radar system, right hail detection methods, and experienced weather professionals must be in place.