Mapping saturated areas with a helicopter‐borne C band scatterometer

Abstract

The “contributing area” concept is one of several basic concepts in modeling hydrologic processes used to explain storm runoff production. The main difficulty in using this concept of variable source areas is the identification and characterization of saturated areas according to the temporal and spatial variability during a storm event. In this experiment a helicopter‐borne C band scatterometer has been used to locate the saturated areas within a small watershed. In contrast to the general results, where radar cross section increases with soil moisture, calibration shows a backscatter coefficient decreasing for the high gravimetric water contents of the saturated areas, which may be due to the increasing importance of specular reflection processes. It appears that a threshold on the backscatter coefficient may be determined which would allow the location of saturated areas, independent of the nature of the field surface (vegetation cover or slope). These experiments, which were intended partly as ERS 1 satellite simulations, show that active microwaves may be a good tool for partial hydrology.

Operational performance of current synthetic aperture radar sensors in mapping soil surface characteristics in agricultural environments: application to hydrological and erosion modelling

“…Surface runoff occurs when rainfall intensity exceeds the soil infiltration capacity or when rainfall volumes exceed the soil storage capacity (Zobeck and Onstad, 1987;Boiffin et al, 1988;Brun et al, 1990;Le Bissonnais, 1990). For both of these variables, in addition to vegetation and pedological characteristics, soil roughness and moisture content play a major role.…”

On constraining TOPMODEL hydrograph simulations using partial saturated area information

“…A remote sensing technique to map saturated areas would be extremely useful, even if repeat times were long or irregular, but most remote sensing methods are limited by insensitivity of emmissivities close to saturation and by image speckle from wet surfaces (e.g. Brun et al, 1990). On the other hand, a perceptual model for the response of this catchment includes the fact that the catchment is very wet for much of the year and that the dynamics of the contributing areas are important for runoff formation.…”

Radar remote sensing of the source areas from the Coët-Dan catchment

“…RESULTS AND DISCUSSION The threshold detection scheme Figure 5 presents the saturated areas predictions for the ground truth zone when a threshold of À7 dB (Brun et al, 1990) is applied to the ®ltered images for Julian days 37, 46 and 82. The major rainfall event of this dry winter occurred between these ®rst two dates, followed by about one month with practically no rain, at the end of which the third image was taken ( Figure 6).…”

“…Based on a helicopter-borne C-band scatterometer and extensive ground experiments over the CoeÈ t-Dan catchment in French Brittany, Brun et al (1990) have proposed mapping of the saturated area extent by applying a threshold on the back-scattering coecient. For the ERS synthetic aperture radar (SAR) con®guration, a threshold value of À7 dB was found independent of the nature of the ®eld surface.…”