Application of SCS Model in Estimation of Runoff from Small Watershed in Loess Plateau of China

Soil Conservation Service (SCS) model, developed by U. S. Soil Conservation Service in 1972, has been widely applied in the estimation of runoff from an small watershed. In this paper, based on the remote sensing geo-information data of land use and soil classification all obtained from Landsat images in 1996 and 1997 and con-ventional data of hydrology and meteorology, the SCS model was investigated for simulating the surface runoff for single rainstorm in Wangdonggou watershed, a typical small watershed in the Loess Plateau, located in Changwu County of Shaanxi Province of China. Wangdonggou watershed was compartmentalized into 28 sub-units according to natural draining division,and the table of curve number (CN) values fitting for Wangdonggou watershed was also presented. During the flood period from 1996 to 1997, the hydrograph of calculated runoff process using the SCS model and the hydrograph of observed runoff process coincided very well in height as well as shape, and the model was of high precision above 75%. It is indicated that the SCS model is legitimate and can be successfully used to simulate the runoff generation and the runoff process of typical small watershed based on the remote sensing geo-information in the Loess Plateau.

Scattering center modeling for low-detectable targets

The scattering centers(SCs)of low-detectable targets(LDTs)have a low scattering intensity.It is difficult to build the SC model of an LDT using the existing methods because these methods mainly concern dominant SCs with strong scattering contributions.This paper presents an SC modeling approach to acquire the weak SCs of LDTs.We employ the induced currents at the LDT to search SCs,and the joint time-frequency transform together with the Hough transform to separate the scattering contributions of different SCs.Particle swarm optimization(PSO)is applied to improve the estimation results of SCs.The accuracy of the SC model built by this approach is verified by a full-wave numerical method.The validation results show that the SC model of the LDT can precisely simulate the signatures of high-resolution images,such as high-resolution range profile and inverse synthetic aperture radar(ISAR)images.

Two universal runoff yield models： SCS vs. LCM

Runoff calculation is one of the key components in the hydrological modeling. For a certain spatial scale, runoff is a very complex nonlinear process. Currently, the runoff yield model in different hydrological models is not unique. The Chinese LCM model and the American SCS model describe runoff at the macroscopic scale, taking into account the rela- tionship between total actual retention and total rainfall and having a certain similarity. In this study, by comparing the two runoff yield models using theoretical analyses and numerical simulations, we have found that： （1） the SCS model is a simple linear representation of the LCM model, and the LCM model reflects more significantly the nonlinearity of catchment runoff. （2） There are strict mathematical relationships between parameters （R, r） of the LCM model and between parameters （S） of the SCS model, respectively. Parameters （R, r） of the LCM can be determined using the research results of the SCS model parameters. （3） LCM model parameters （R, r） can be easily obtained by field experiments, while SCS parameters （S） are difficult to measure. Therefore, parameters （R, r） of the LCM model also can provide the foundation for the SCS model. （4） The SCS model has a linear relationship between the reciprocal of total actual retention and the reciprocal of total rainfall during runoff period. The one-order terms of a Taylor series expansion of the LCM model describe the same relation- ship, which is worth further study.