Thursday, 31 August 2017
Zurich DEFG (Swissotel Chicago)
The weather radar has provided useful information about hydrometeors for various meteorological and hydrological applications and it can observe various parameters for meteorological phenomena with high spatio-temporal resolution on wide observational areas. However, it suffers from many error sources such as radar calibration, beam shielding, attenuation, bright band contamination, beam broadening, anomalous propagation, etc. Furthermore, non-meteorological echo such as ground clutter, sea clutter and chaff causes severe errors when radar variables are quantitatively used. In particular, Korea has many mountainous areas and is surrounded by water on three sides. Chaff echo due to flight training also occurs frequently. Thus, proper technique to avoid the effects of these error sources is necessary for quantitative use of radar observables in Korea.
One of the techniques to overcome these error sources is to consist of the observable-lowest elevation surface, hybrid surface, in radar volume scan that is immune to ground clutter contaminations, radar beam blockage and other non-meteorological echoes. Many researchers have explored this hybrid surface technique to improve the accuracy of radar rainfall estimation, so-called Hybrid Surface Rainfall(HSR)(e.g., Shedd et al., 1989, 1991; O’Bannon, 1997; Fulton et al., 1998; Maddox et al., 2002; Zhang et al., 2011; Kwon et al., 2012a).
In this study, the radar rainfall estimation algorithm based on hybrid surface technique was developed for improvement the accuracy in quantitative precipitation estimation and application to operational radar network in Korea. The algorithm consists of the observable-lowest elevation surface considering 1) radar beam shielding fraction, 2) ground clutter, 3) other non-meteorological echoes, sequentially. Beam shielding areas were identified and discarded based on simulated beam blockage fraction based on standard refraction and two-way gaussian beam pattern using digital elevation model(DEM). Ground clutter area were determined by apply threshold to the radial texture of reflectivity. Other non-meteorological echoes were considered by fuzzy logic-based quality index and the characteristics of dual-pol variables. The rain rate based on hybrid surface reflectivity was evaluated quantitatively using dense rain gauge network for the rain cases of narrow frontal system, wide spread precipitation(stratiform), and summer monsoon(changma system).
One of the techniques to overcome these error sources is to consist of the observable-lowest elevation surface, hybrid surface, in radar volume scan that is immune to ground clutter contaminations, radar beam blockage and other non-meteorological echoes. Many researchers have explored this hybrid surface technique to improve the accuracy of radar rainfall estimation, so-called Hybrid Surface Rainfall(HSR)(e.g., Shedd et al., 1989, 1991; O’Bannon, 1997; Fulton et al., 1998; Maddox et al., 2002; Zhang et al., 2011; Kwon et al., 2012a).
In this study, the radar rainfall estimation algorithm based on hybrid surface technique was developed for improvement the accuracy in quantitative precipitation estimation and application to operational radar network in Korea. The algorithm consists of the observable-lowest elevation surface considering 1) radar beam shielding fraction, 2) ground clutter, 3) other non-meteorological echoes, sequentially. Beam shielding areas were identified and discarded based on simulated beam blockage fraction based on standard refraction and two-way gaussian beam pattern using digital elevation model(DEM). Ground clutter area were determined by apply threshold to the radial texture of reflectivity. Other non-meteorological echoes were considered by fuzzy logic-based quality index and the characteristics of dual-pol variables. The rain rate based on hybrid surface reflectivity was evaluated quantitatively using dense rain gauge network for the rain cases of narrow frontal system, wide spread precipitation(stratiform), and summer monsoon(changma system).
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