Soil surface roughness in temperate forest during SMAPVEX19-22

Authors: WALKER, V - Oak Ridge Institute For Science And Education (ORISE); Cosh, Michael; White, William; COLLIANDER, A - California Institute Of Technology; KELLY, V - Cary Institute Of Ecosystem Studies; SIQUEIRA, P - University Of Massachusetts, Amherst

Submitted to: IEEE Journal of Selected Topics in Applied Earth Observations and Remote Sensing
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/1/2025
Publication Date: 1/15/2025
Citation: Walker, V.A., Cosh, M.H., White, W.A., Colliander, A., Kelly, V., Siqueira, P. 2025. Soil surface roughness in temperate forest during SMAPVEX19-22. IEEE Journal of Selected Topics in Applied Earth Observations and Remote Sensing. 18:4640-4647. https://doi.org/10.1109/JSTARS.2025.3530710.
DOI: https://doi.org/10.1109/JSTARS.2025.3530710

Interpretive Summary: Surface roughness of the soil impacts remote sensing and thus impacts any remote sensing product that is based upon microwave frequencies. The application of these frequencies to forested landscapes is relatively new so there has been little investigation into the surface roughness of forest soils. An investigation of the roughness of two forest domains was conducted to support microwave remote sensing observations in 2022 in a New York and a Masschusetts forest. It was determined that when freshly fallen surface debris was removed, the forest floor was very smooth with vary little roughness, much smoother that agricultural fields that have tillage and other activity. This is useful for foresters and remote sensing scientists who will need this information to interpret forest remote sensing products.

Technical Abstract: Data were collected across multiple forested domains during the Soil Moisture Active Passive alidation Experiment 2019-2022 (SMAPVEX19- 22) to improve understanding of soil moisture retrievals under dense vegetation. Soil surface roughness was one of many soil and vegetation parameters sampled during intensive operations periods during the spring and summer of 2022 because of its importance to retrieval accuracy (rougher soils have a higher emissivity and reduced sensitivity to soil moisture compared to smooth soils with otherwise identical characteristics). A total of 410 valid pinboard transects were collected across 24 sites between the two temperate forest domains located in the northeastern United States. Two experimental methods (handheld lidar and ultrasonic robot) were additionally tested at select sites. After removal of topographic slope, the forest floor was found to be rela tively smooth with average rms heights of 9 ± 1 mm in the central Massachusetts domain and 6 ± 1 mm in the Millbrook, New York domain. These correspond to estimates of the model roughness parameter, h, of 0.31 and 0.16, respectively, which is within the range of accepted lookup table values but smoother than suggested by recent studies retrieving h over forests.