Remote sensing of hydrological fluxes

Abstract

Remote sensing is developing as a measurement technique to the point where data are starting to be used operationally in a quantitative way other than just in weather forecasting. In addition, many other uses of the data are being developed because of the sparseness of conventional data in many parts of the world. A recent session of AGU's Hydrology Section at the Spring Meeting in Baltimore, Md., featured discussions of some of the recent advances in the use of remotely sensed data to estimate hydrological fluxes.Several papers dealt with remote sensing aspects of the First ISLSCP Field Experiment (FIFE), following another session of the Hydrology Section, which discussed nonremote sensing results from FIFE. S. N. Goward (University of Maryland, College Park) presented a review of empirical results from time series of Advanced Very High Resolution Radiometer at the FIFE site and their relationship to some conventional observations. He showed strong relationships between spectral vegetation indices and surface temperature with scatter being at least partly caused by surface moisture variations. Unraveling the relationships from a physical point of view will involve a greater understanding of atmospheric effects and surface properties from other concurrent measurements during FIFE. Similar relationships between spectral vegetation indices and surface temperature were observed and reported by C. L. Walthall (University of Maryland, College Park), who used a radiometer mounted on a helicopter to collect data at the FIFE site. This indicates that the relationships are not entirely due to atmospheric effects. M. F. Jasinski and P. S. Eagleson (Massachusetts Institute of Technology, Cambridge) described a theoretical reflectance model for spectral vegetation indices in terms of ground cover that will be extremely useful in interpreting these experimental results. R. N. Halthore (Applied Research Corp., Landover, Md.) described some of the measurements of aerosols during FIFE, in a paper coauthored by R. S. Fraser (Goddard Space Flight Center, Greenbelt, Md.), R. Ferrare (University of Maryland, Greenbelt) and T. O. Aro (University of Ilorin, Nigeria). Their results disagree with some others collected during FIFE by other investigators: all measurements have to be reconciled. J. R. Wang (Goddard) in a paper coauthored by J. C. Shiue (Goddard), T. J. Schmugge (USDA, Baltimore, Md.), and E. T. Engman (USDA, Beltsville, Md.) described some of the measurements of soil moisture made using an airborne L‐band passive microwave radiometer on the FIFE site. These estimates were shown to be replicable over several years, although there was some sensitivity to whether the vegetation in the area had been burned the previous year. All the FIFE investigators are now only starting to look at several sets of data of different types, and use them together, and to begin to look at the problem of relating observations taken at different spatial scales.