Demonstration of a Visible and Near-infrared Illuminated Penetrometer Probe for In Situ Subsurface Soil Interrogation
David J. Brown, Washington State University
This paper was presented at the Art, Science and Applications of Reflectance Spectroscopy Symposium sponsored by ASD Inc. and IEEE GRSS, February 23-25, 2010 in Boulder, Colorado.
Authors: David J. Brown, Ross S. Bricklemyer
Affiliation: Washington State University, Pullman, WA USA
Abstract
Visible and near-infrared (VisNIR, 400-2500 nm) diffuse reflectance spectroscopy is a rapid, inexpensive soil characterization method that has proven capable of quantifying constituents of dried and ground soil samples. However, very little is known about how VisNIR performs in a field setting on soils interrogated in-situ. Commercial VisNIR probes have only recently become available, and there is little information on the performance of these probes relative to previously published interrogations of intact soil materials using standard VisNIR contact probes. Here we present preliminary data on the performance of a VisNIR soil probe that supports in situ interrogation of soils to a depth of 1 m with an Analytical Spectral Devices AgriSpec® spectrometer (350-2500 nm, ASD Inc., Boulder, CO, USA). To evaluate this instrument, we have conducted two experiments. First, we interrogated dried soil samples and other standard optical materials in the laboratory using both the VisNIR soil penetrometer and the ASD contact probe to quantify any loss in signal quality associated with the longer fiber optics and “periscope” optics of the penetrometer. Secondly, we interrogated a complex experimental farm with loess soils (silt to silty clay loams) adjacent to several hundred locations where soil cores were earlier extracted and analyzed. Though we have experienced a signal-to-noise degradation across the VisNIR spectrum with the penetrometer relative to the ASD contact probe, this instrument shows promise for rapid, semi-quantitative in situ soil characterization.