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Research Project: Understanding Water-Driven Ecohydrologic and Erosion Processes in the Semiarid Southwest to Improve Watershed Management

Location: Southwest Watershed Research Center

Title: An improved excavation method for measuring bulk density of rocky soil using terrestrial LiDAR

item Polyakov, Viktor
item Nearing, Mark
item Nichols, Mary
item Cavanaugh, Michelle

Submitted to: Journal of Soil and Water Conservation
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/3/2019
Publication Date: 6/3/2019
Citation: Polyakov, V.O., Nearing, M.A., Nichols, M.H., Cavanaugh, M.L. 2019. An improved excavation method for measuring bulk density of rocky soil using terrestrial LiDAR. Journal of Soil and Water Conservation. 74(3):265-268.

Interpretive Summary: Soil density near the surface is important to know for a variety of reasons, but is a difficult measurement to make in stony soils. Traditional and otherwise well-accepted methods are not conducive to accurate application when soils contain high levels of stones and gravel. Terrestrial lidar is a surveying method that very precisely measures the distance to a body of interest using a pulsating laser light and then detecting the reflected pulses with very accurate timing. It is a highly sensitive technique that allows for very precise mapping of surfaces. It is commonly used to create detailed surface maps for various applications. In this study we used the lidar technique to accurately measure the density of stony surface soils. Undisturbed soil surfaces were scanned, a hole was dug to the desired depth or interest, and the contour of the resulting surface was again scanned with the lidar. The difference between surface scans indicated the volume of the hole, and the weight of the soil removed was then used with the measured volume to calculate the soil density. The small variations between replicates measurements indicated that the method was quite accurate. This method will provide a way to measure soil density in these otherwise difficult-to-measure soil materials.

Technical Abstract: A new method to estimate soil bulk density of rocky soil is presented. The method utilizes soil surface scanning with terrestrial lidar. It allows to determine volumes of comparatively large samples and measure several of them at a time. The experimental procedure also eliminates the need for reference points. All this contributes to low variability of measurements and decreases time in the field. The average bulk density of Luckyhill very gravely sandy loam from southern Arizona was 1.48 g cm-3 with standard deviation of 5.4%, while the same determined by a traditional excavation method was 1.45 g cm-3 with standard deviation of 10.3%.