摘要
为提高洪水设计值 X_p 的有效性,本文提出了一种新的参数估计方法—下限法.其基本原理在于:首先在原始空间用概率权重矩法确定出位置参数α_0的估计值_0,然后将洪水系列 x 由原始空间转换到变换空间 y,变换后的系列 y=x-_0即服从二参数的伽玛分布。在 y 域中,用概率权重矩法或用自协方差法估计出 y 域的参数,最后换算到 x 域。统计试验的结果表明:下限法所得的设计值 X_p 的无偏性和有效性显著优于矩法,和概率权重矩法相比,无偏性大致相当,但有效性较优。
A new procedure,the method of lower-bound(MLB),is proposed for determining the design quantile Xp.The basic concept is:first to determine an estimate _0 of the location parameter a_0 using the PWM method,and then,to transform the variable X from original(X)space to a new(Y) space by using Y=X-_0.The variable Y is considered to have a 2-para- meter Gamma distribution.In Y-space the two parameters are estimated by the PWM method or an autocovariance method.then transformed from Y- space to X-space.The results from the Monte Carlo experiments show that the estimates of MLB is less biased than MOM's and more efficient than PWM's for design quantiles Xp.
关键词
洪水频率
分布参数
P-Ⅲ型
下限法
the method of Lower-bound
original space
transformed space
probability weighted moments
autocovariance
