Determining the Utility of Synthetic Aperture Radar (SAR) in Estimating Surface Soil Moisture Conditions for Trafficability Analyses; Phase III Progress Report
Dates
Year
2000
Citation
Hinzman, L. D., Nolan, M., Prokein, P., Fatland, R., Gentry, J. F., and Johnson, B. C. J., III, 2000, Determining the Utility of Synthetic Aperture Radar (SAR) in Estimating Surface Soil Moisture Conditions for Trafficability Analyses; Phase III Progress Report: Water and Environmental Research Center, University of Alaska Fairbanks: Fairbanks, v. INE/WERC 00.07, 34 p.
Summary
Introduction Improving vehicle trafficability planning is a major defense mission, and we believe that this research has made significant improvements towards this end. We are striving to develop new space-borne Synthetic Aperture Radar (SAR) techniques to measure temporal changes in soil moisture, soil freeze/thaw state, and snowmelt, utilizing both amplitude and phase signal information. Such knowledge is of great use to a variety of end-users. Military planners need to predict the bearing strength of the underlying soil and thus the number and weight of vehicles able to travel across it. Global climate modelers need to know the surface greenhouse gas and latent heat flux. The common variables in these applications are soil moisture, [...]
Summary
Introduction Improving vehicle trafficability planning is a major defense mission, and we believe that this research has made significant improvements towards this end. We are striving to develop new space-borne Synthetic Aperture Radar (SAR) techniques to measure temporal changes in soil moisture, soil freeze/thaw state, and snowmelt, utilizing both amplitude and phase signal information. Such knowledge is of great use to a variety of end-users. Military planners need to predict the bearing strength of the underlying soil and thus the number and weight of vehicles able to travel across it. Global climate modelers need to know the surface greenhouse gas and latent heat flux. The common variables in these applications are soil moisture, snowmelt, and soil moisture phase (frozen or thawed) over large, often remote areas, over short time intervals. Our techniques involve multi-temporal amplitude comparisons, SAR interferometry, expert hydrological systems, artificial neural networks, and new geo-spatial/temporal data representation techniques. The basis of this research is that because the dielectric properties of soils change with varying moisture content (or snow melt or frozen/unfrozen ground), both the amplitude and phase of the signal received by the SAR satellites will change as well. Our approach to this type of research in the past has made extensive use of field data for ground truthing. In this report we present field results from the Pinon Canyon Maneuver Site (PCMS; managed by Ft. Carson in Colorado Springs) in southern Colorado and Caribou Poker Creeks Research Watershed (CPCRW) near Fairbanks, Alaska. PCMS is reserved for major tank maneuvers, and has an excellent reputation for range management. In particular, the range managers are very sensitive to the role that soil moisture plays in damage to the site, and restrict maneuvers to areas in which long-term traffic-related damage will be minimal. CPCRW is a research watershed in the boreal forest of Subarctic Alaska where we are concurrently conducting other hydrologic studies that provide complementary data needed for these analyses. This project uses new and innovative SAR techniques to solve problems related to vehicle trafficability and global climate change, namely remotely-sensed soil moisture measurement. We have three main objectives for this project: 1) Build on the existing uses of SAR by developing new techniques for its implementation, 2) Continue our field data collection efforts in the Pinon Canyon Maneuver Site (PCMS; managed by Ft. Carson in Colorado Springs) and Caribou Poker Creeks Research Watershed (CPCRW), and 3) Initiate development of prototype applications of vehicle trafficability planning for national decision makers relying on timecritical geospatial information. Conclusions Results to date indicate satellite borne synthetic aperture radar is a promising tool for estimation of ground surface condition. Several analyses techniques are being examined. Our analysis approaches are changing from doing direct comparisons of field measured soil moisture with SAR reflectance values, to more refined comparisons. Interferometric analyses appear very promising, demonstrating marked responses to rainfall events. Coherograms also appear to be a valuable approach to detect changes. Through a Quadtree analysis, it should be fast and easy to quantitatively map specific areas of interest to soil moisture levels. Further, an analysis tool named SARfari is being developed to compartmentalize analysis techniques, enabling a trained user to quickly examine SAR imagery for field analyses of surface condition over broad areas. A spatially distributed hydrological model has been applied to the Pinon Canyon Maneuvering Site to enable a more compatible comparison of soil moisture levels simulated on similar spatial scales by two independent techniques. Although not fully calibrated yet, the hydrologic model is performing quite well and the broader comparisons (over large spatial areas and numerous satellite viewing dates) will permit further refinement f SAR analysis techniques.
