Multisensor Hydrologic Assessment of a Freshwater Wetland

Abstract

This article evaluates the use of synthetic aperture radar (SAR) and visible/infrared (VIR) satellite imagery for mapping the extent of standing water in the Peace-Athabasca Delta during spring and summer of 1998. SAR images contain data about the geometric and electrical characteristics of the objects, while VIR images contain information about the reflectivity of objects. Radar pulses can also penetrate vegetation to some degree depending on the wavelength and vegetation thickness. It is hypothesized that since Radarsat and SPOT images contain complementary information, flood mapping will be more efficient when the two image types are used in combination. Radarsat SAR and SPOT multispectral imagery from May 1998 and July 1998 were used for the flood mapping. A Radarsat S2 image (27.5° incidence angle) was obtained for May 1998. To evaluate the incidence angle effect on flood mapping, a Radarsat S1 image (27.5° incidence angle) and a Radarsat S7 image (47.0° incidence angle) were obtained for July 1998. The Radarsat scenes were calibrated and filtered, and all imagery were orthorectified to minimize geometric distortion. A Mahalanobis distance algorithm was used to classify the SPOT scenes, the Radarsat scenes, and a combination of the two into open water, flooded vegetation, and nonflooded land. The results indicate that flood mapping in both spring and summer conditions has significantly higher accuracy when Radarsat and SPOT imagery are used in combination, rather than separately. However, it is important to use Radarsat imagery acquired at low incidence angles. Classification of the SPOT scene combined with the Radarsat S1 scene achieved significantly better results than those obtained when the SPOT scene was classified in combination with the Radarsat S7 scene.