Penetrometer-Mounted Visnir Spectroscopy: Assimilating in-Situ Spectra with Dry, Ground Spectral Libraries.

Visible, near inferred (VisNIR) spectroscopy has become a common technique for measuring soil properties of dried and ground laboratory soil samples.  Recently, technologies have emerged to allow for the rapid collection of VisNIR spectra in the field.  Soil scientists have lauded these in situ VisNIR sensors as important tools for on-the go soil sensing; however, the application of such sensors has been limited.  A major challenge for in situ VisNIR spectroscopy is that, unlike laboratory samples, soil in the field is heterogeneous and contains variable amounts of soil moisture.  For VisNIR spectroscopy to be applied in situ, either new in situ spectral libraries must be collected or methods must be developed to utilize existing laboratory spectral libraries.   In this study we demonstrate the application of dry-ground spectral libraries to prediction of soil properties from in situ VisNIR.  In situ VisNIR spectra were collected using a penetrometer mounted spectrometer.  Soil properties (e.g. clay and organic carbon content) were then predicted using the in situ VisNIR spectra and an existing dry-ground spectral library.  Results show that the preexisting library can successfully predict in situ soil properties with accuracy comparable to that of predictions made on VisNIR spectra collected on laboratory samples.