中文摘要：

该文利用反演工具UCODE与4种Richards方程数值模型（Ross模型、Picard-θ模型、Picard-mix模型和Picard-h模型）进行耦合,构建了4种不同的反演模型。基于田块尺度含水率观测数据,分别用4种反演模型优化了研究田块的土壤参数。研究结果表明,4种模型的反演精度依次为：Ross模型、Picard-θ模型、Picard-mix模型和Picard-h模型,但差异并不显著,反演效率以Ross模型最优。随着网格的加密,各种模型所反演参数的模拟精度改善不明显。本文还讨论了土壤水运动中＂异参同效性＂现象,并提出＂参数曲线带＂的概念——即由反求的同效参数土壤水分曲线和水力传导度曲线形成的包络图。随着模拟精度要求越高,同效参数越少,＂参数曲线带＂越窄,并认为反求的同效参数曲线在含水率观测信息较多的地方交汇。

英文摘要：

Unsaturated zone hydrological processes played an important role between the processes of surface and groundwater hydrology. The Richards＇ equation was widely utilized to describe unsaturated zone flow due to its solid physical foundation. It was essential to know the parameters of this equation before simulation, and these parameters were also called as soil hydraulic parameters in this paper. Comparing with experimental methods, the inverse method was a more realistic way to obtain parameters. Universal Inverse Code（UCODE） using gradient-type minimization method provided users with flexibility in estimating parameters of forward models. However, there were many numerical methods to solve Richards＇ equation, and four representative numerical models discussed in this paper were Ross model, Picard-θ model, Picard-mix model and Picard-hmodel, respectively. It had been known that the Ross model was of the most computational efficiency, while Picard-h model may lead to serious mass balance problem. Based on the combination of UCODE and four numerical models of Richards＇ equation, four different inverse models of unsaturated flow were constructed in this paper to optimize three parameters of Richards＇ equation, i.e., Ks（Saturated Hydraulic Conductivity）, α（Reciprocal of Air Entry Pressure） and n（Grain Size Distribution Parameter）. In this paper, a ten days infiltration test was conducted in a 7.77 m ×29.38 m area located in Wuhan University Water Conservancy and Water Environmental Laboratory（China）, and observed data was the soil water content measured by TRIME-PICO IPH system. Every 24 hours was as an irrigation-measurement period. The upper boundary flux Ra[L/T] changed with time. More specifically, Ra was 80 mm/d during the first 3 hours, while it was 0 mm/d in the last 21 hours. Before the infiltration test, Ks was measured directly by 29 double rings, and the others parameters were measured by centrifugal method（4 filled samples and 36 undisturbed samples）. The parameters Ks an