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Title:   Author  item
                                            Walthall, Charlesitem
                                            Gish, Timothyitem
                                            CHINKUYU, A - UNIV. CAitem
                                            Dulaney, Wayneitem
                                            Kaul, Monishaitem
                                            Daughtry, Craig
  Submitted to: IEEE IGARSS Annual Proceedings
                                    Publication Type: Proceedings
                                    Publication Acceptance Date: 7/15/2004
                                    Publication  Date: 9/20/2004
                                    Citation: Walthall, C.L., Gish, T.J., Chinkuyu, A., Dulaney, W.P., Kaul, M.N., Daughtry, C.S. 2004. Analysis of surrogate indicators for evidence of subsurface preferential flow pathways: Impact of subsurface preferential flow on varibility of NDVI. In: Proceedings of the 2004 IEEE International Geoscience and Remote Sensing Symposium, September 20-24, 2004, Anchorage, Alaska. VI:3992-3995.Interpretive Summary:
                                Technical Abstract: Watershed-scale processes governing chemical fluxes to adjacent ecosystems are so poorly understood that strategies for mitigating chemical contamination cannot be formulated. Characterization of hydrologic processes and chemical behavior at the watershed scale is critical to the development of sustainable agricultural practices. Identifying locations for monitoring hydrologic processes like subsurface preferential flow is difficult because conventional sampling methods are inadequate for measuring this highly variable, critical process.  A method for detecting and mapping subsurface preferential flow pathways was developed that is based on ground-penetrating radar (GPR) data and digital elevation maps (DEM).  This procedure was confirmed for a cornfield in Maryland using real-time soil moisture data, maps of within-field grain yield, and remotely sensed imagery of the field. Unfortunately, it is economically unfeasible and logistically impractical for producers to use the GPR-DEM procedures to map subsurface preferential flow pathways for all crop fields.  It may, be possible to use remotely sensed imagery, grain yield maps, and a DEM as surrogate indicators of subsurface preferential flow pathways occurring at or near crop rooting depth.  Image NDVI was found to increase NDVI with distance from pathways during normal rainfall.  Imagery collected during drought conditions shows a decrease of NDVI with distance from flow pathway.  The drought year imagery appears especially useful as only within-field locations with subsurface irrigation from preferential flow pathways maintain vigor.  It is suggested that maps of vegetative productivity derived from remotely sensed imagery may be more useful than within-field grain yield maps for detecting and delineating locations of subsurface preferential flow pathways. The ability to delineate within-field locations with a high probability of subsurface preferential flow pathways will allow producers to better manage crop production, and mitigate losses of agricultural chemical inputs to neighboring ecosystems and waterways


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