In-Situ Application of Near Infrared Reflectance Spectroscopy to Soils

Recent environment developments have created increased demand for in-field measurement of soil constituents. Soil carbon measurements are needed to study carbon sequestration and measurements of soil nitrogen could be used to manage and minimize the leaching of nitrates into the ground water. Near infrared reflectance spectroscopy is an optical method that has shown good results in the laboratory for measuring soil carbon, soil nitrogen and other soil constituents. If this method could be applied in-situ without substantial loss of measurement accuracy, then a rapid field analysis of soil would be possible. Previous attempts have used designs that were prone to interference from dust and mud. This research proposes a method of performing in-situ optical measurements through a sapphire window. The sapphire, which has good optical qualities and is extremely durable, is pressed against the soil to maintain a smooth and consistent sample geometry. The window will be used to measure soil spectra in both a stationary mode and a non-stationary mode. Multivariate statistical analysis will then be used to correlate the spectra to levels of various soil constituents including carbon and nitrogen. These results will be compared to a similar analysis of spectra acquired in the laboratory.