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| Science Results (Summer 2006) |
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**Mapping surface roughness and soil moisture using multi-angle imagery without ancillary data
 
Rahman, M.M.             University of Arizona
Moran, M.S.                            SouthwestWatershedResearchCenter
Thoma, D.P.                             University of Arizona
Bryant, R.                                 University of Arizona
Holifield Collins, C.D.   SouthwestWatershedResearchCenter
Jackson, T.J.                            Hydrology and Remote Sensing Lab
Orr, B.J.                                   University of Arizona
Tischler, M.                              US ARMY
 
Information about the distribution of surface soil moisture is important for management of agriculture and natural resources.  Theoretically, soil moisture information can be obtained from a satellite image of radar backscatter in combination with a backscatter simulation model.  In practice, this approach is untenable because the model requires information about surface roughness, which is rarely known.  This study proposes a new way to parameterize the backscatter model by using two radar images acquired at two incident angles.  The surface roughness is determined from the multi-angle radar, and consequently, the radar model can be used to determine surface soil moisture from imagery acquired at any time.  When tested for a semiarid watershed over a one-year period, this approach derived regional soil moisture estimates that compared well with ground-based measurements.  Also, the implementation of this method is rather straight-forward and can be applied operationally at locations where field data are not available.  This could be a feasible and economic approach for mapping surface soil moisture over large, inaccessible regions for such important applications as flood prediction and drought assessment.

 
**Spatial and temporal variability in evapotranspiration estimates from AVIRIS at the SMEX04 site
 
Kim, H.                                    University of Arizona
Huete, A.R.                              University of Arizona
Nagler, P.                                 University of Arizona
Glenn, E.P.                               University of Arizona
Emmerich, W.E.                       SouthwestWatershedResearchCenter
Scott, R.L.                               SouthwestWatershedResearchCenter
 
Determining water movement in arid environments is critical to understanding how the ecosystem functions.  Evapotranspiration (ET) the evaporation of water from the soil surface and the transpiration of water through plants can be measured at points on the landscape.  To comprehend the water movement we must know how ET changes spatially and with time on the landscape.  Remote sensing of the vegetation and soil surface using aircraft and satellites has been successful in making estimates of ET at the point of measurement.  This work has determined the appropriate scales to make the remote sensing measurements to scale the ET measurements up from points to the landscape level and the times the remote sensing estimates of ET are most accurate.   The study will allow cost effective estimates of landscape ET measurements to improve water budgets and potentially water supplies.  
 
**A new sensitivity analysis framework for model evaluation and improvement using a case study of the Rangeland Hydrology and Erosion Model
 
Wei, H.                                    University of Arizona
Nearing, M.A.                          SouthwestWatershedResearchCenter
Stone, J.J.                                SouthwestWatershedResearchCenter
 
Complex computer models are used in the field of natural resource management for many purposes.  Because of the complexity of the numerical models used, and the large numbers of input factors there is a high risk for these models of having problematic or nonsensical model responses in certain applications. Sensitivity analysis (SA) is a useful tool for ascertaining whether model response is logical and reasonable.  This paper describes a new method for conducting this type of analysis and it describes how to use the method for identifying model deficiencies and improving model function. The method was applied to the Rangeland Hydrology and Erosion Model (RHEM), using soil erosion response as a case study. Results of the study showed that the sensitivity of the model to changes in site conditions was interdependently related to all the other the input parameter values in a complex manner. The paper also shows how this method, combined with techniques such as statistics and scatter plots, can be used effectively to know which of the input variables are most critical to proper functioning of the model and to identify incorrect relationships in the model. The paper shows how this method can be used as an element of the iterative modeling process whereby model response can be surveyed and problems identified and corrected in order to construct a robust model.  This work will help us to develop better tools for the management of natural resources across the United States.
 
**Effects of rock fragments incorporated in the soil matrix on concentrated flow hydraulics and erosion
 
Rieke-Zapp, D.                        University Berne, Switzerland
Poesen, J.                                 University  Leuven, Belgium
Nearing, M.A.                          SouthwestWatershedResearchCenter
 
Rocks in the soil profile have a dramatic effect on soil erosion, both in terms of how much erosion occurs during a rainstorm and where it occurs on the landscape.  In certain environments the effect of rocks can be very dominant.  In this study we looked quantitatively at the impacts of rocks on erosion rates.  We did this by placing soil with different amounts of rocks added in a controlled laboratory flume and measuring the soil that was eroded and the shapes of the rill patterns that formed.  We found that rate of erosion dropped dramatically with a very small presence of rocks.  We also found that rills forms in the soil with rocks were much wider, and flow depths much less than in soil without rocks.  We will use this information to develop algorithms for computer-based soil erosion models that are used to predict soil erosion in different environments.  These models are used for helping farmers and ranchers develop soil conservation plans on the land, for engineering design purposes, and for implementing national soil conservation programs.  Thus, this study will lead to better soil conservation planning tools for the United States.
 
 
**Effects of precipitation pulse sequencing on plant and soil response to pulse size in the****Sonoran********Desert**** 
Cable, J.M.                              University of Arizona
Pavao-Zuckerman, M.A.          University of Arizona
Scott, R.L.                               SouthwestWatershedResearchCenter
Huxman, T.E.                           University of Arizona
 
Discrete "pulses" of precipitation drive biological activity in arid and semi-arid ecosystems, but all pulse events may not have similar effects. Pulses differ in their sequence in time influencing antecedent soil moisture conditions prior to a subsequent rain event that can affect biological responses. In this study, we examined how a short sequence of rainfall events precondition the activity of microbes and plants and alter their responsiveness to different sized rainfall events.  In a SonoranDesert grassland, we applied an initial "preconditioning" pulse along with a series of different sized rainfall events and sampled soil, leaf, and root carbon dioxide exchange along with other environmental conditions.  We found that preconditioning did not affect the responsiveness of soil respiration to different sized target pulses.  However, preconditioning influenced both the responsiveness and duration of activity for plant photosynthesis following different sized target pulses.  Rainfall variability is expected to increase in the deserts of southwestern US, possibly resulting in non-linear responses of ecosystem carbon processes due to the differential response of plants and soils. Return to top                Last Modified:6/26/2018            Connect with ARSSign up-  ARS Home 
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