ADVANCES IN ATMOSPHERIC SCIENCES, VOL. 24, NO. 5, 2007, 893–906 An Improved Velocity Volume Processing Method LI Nan ∗ 1,2 ( ), WEI Ming 3 ( ), TANG Xiaowen 1 ( ), and PAN Yujie 1 ( ) 1 Key Laboratory of Mesoscale Severe Weather of Ministry of Education, Nanjing University, Nanjing 210093 2 Global Change Research Center, Nanjing University, Nanjing 210093 3 Jiangsu Key Laboratory of Meteorological Disaster, Sino-American Cooperative Remote Sensing Center, Nanjing University of Information Science and Technology, Nanjing 210044 (Received 20 March 2006 revised 22 January 2007) ABSTRACT Velocity volume processing (VVP) retrieval of single Doppler radar is an effective method which can be used to obtain many wind parameters. However, due to the problem of an ill-conditioned matrix arising from the coefficients of equations not being easily resolved, the VVP method has not been applied adequately and effectively in operation. In this paper, an improved scheme, SVVP (step velocity volume processing), based on the original method, is proposed. The improved algorithm retrieves each group of components of the wind field through a stepwise procedure, which overcomes the problem of an ill-conditioned matrix, which currently limits the application of the VVP method. Variables in a six-parameter model can be retrieved even if the analysis volume is very small. In addition, the source and order of errors which exist in the traditional method are analyzed. The improved method is applied to real cases, which show that it is robust and has the capability to obtain the wind field structure of the local convective system. It is very helpful for studying severe storms. Key words: velocity volume processing (VVP), ill-conditioned matrix, stepwise retrieval, residual radial velocity DOI: 10.1007/s00376-007-0893-0 1. Introduction When used in meteorology after World War II, Doppler radar exhibited its effectiveness and efficiency as an active remote sensing system. From then on, studies on the problems of Doppler radar analysis be- came important in meteorological observations and re- search. Whereas a single Doppler radar yields only radial velocity, every attempt to gain the vector wind field must involve some hypotheses or simplifications. Since Lhermitte and Atlas proposed the VAD (velocity azimuth display) (Lhermitte and Atlas, 1961) single- Doppler method applicable to a uniform wind field, a number of studies have been devoted to retrieving two- dimensional or three-dimensional wind fields. These methods mainly include VAD (Caton, 1963; Brown- ing and Wexler, 1968), EVAD (extended velocity az- imuth display) (Srivastava et al., 1986), CEVAD (con- current extended velocity azimuth display) (Matejka, 1993), VARD (velocity area display) (Easterbrook, 1975), BVP (band velocity processing) (Johnston and Marwitz, 1990), VAP (velocity azimuth processing) (Tao, 1992), and VVP (velocity volume processing) (Waldteufel and Corbin, 1979). In addition, many sophisticated dynamical retrieval methods in a vari- ational framework (Kapitza, 1991; Sun et al., 1991; Qiu and Xu, 1992; Laroche and Zawadzki, 1994; Xu et al., 1994a,b; Wei et al., 1998; Gao et al., 2001; Liu et al., 2005) and dual-Doppler radar retrieval meth- ods (Miller and Strauch, 1974; Brandes, 1977; Gao et al., 1999) have also been introduced. However, be- cause dynamical retrieval brings with it many extra factors and assumptions during the calculation pro- cess, and dual-Doppler radar retrieval is confined by the match of time and space, both more or less degrade the accuracy and are difficult to be put into operation. Therefore, non-dynamical retrieval methods for single- Doppler radar are still worth studying. ∗ Corresponding author: LI Nan, shangjineh@163.com