Submitted to: International Soil Tillage Research Organization Proceedings
Publication Type: Proceedings
Publication Acceptance Date: July 1, 2000
Publication Date: N/A
Interpretive Summary: The soil surface has a distinctive shape that affects how the soil absorbs water, washes during rainfall or blows away during strong winds. Scientists use descriptions of the soil surface features in models that estimate water flow in the through soils and that predict wind and water erosion. Instruments aboard airborne aircraft or satellites have been used dto measure the soil surface reflectance. This paper reports on a study that relates the reflectance measurements taken aboard airborne sensors to soil surface shape. The study found that mathematical descriptions of surface shape can be successfully predicted using data collected by the airborne sensors. The study found that the best time to make the measurements were in mid-morning and mid-afternoon. The predictions were not as reliable when the soil was considerably shadowed and when the sun was directly overhead.
Technical Abstract: Soil surface roughness is an important surface soil characteristic used in water and wind erosion prediction equations and numerous applications in hydrology, agroclimatology, and other areas. Aircraft and space-based remote sensing systems have been used to remotely measure soil roughness using spectral radiometers. However, calibration of the space-based measurement systems with land-based methods is needed. In this study, we evaluate the usefulness of using remotely sensed soil surface reflectance data to estimate soil surface roughness. We tested four levels of tillage-induced surface roughness of a fine sandy loam soil using triplicate plots of each level. Ridge height, random roughness, and soil surface wind erosion roughness parameters were measured using a laser roughness meter. Soil surface reflectance was measured at five hourly intervals, starting about one hour after sunrise, using a hyperspectral radiometer. The soil surface wind erosion roughness parameters were used to determine the soil surface shading by applying the sun angle to the cumulative shelter angle distribution. The sunlit fraction was only different among roughness levels at 0800 h and 0900 h yet reflectance measurements were significantly correlated (P<0.05) with all roughness indexes tested. This study suggests that in this area the best time to make roughness index estimates, using reflectance measured from an airborne platform in the summer, is between 0900 h and 1100 h, CDT and at times with similar sun angles after solar noon.