Micro Side-Viewing Optical Probe for VNIR-DRS Soil Measurement

In this paper, we present the design, fabrication and testing of a new micro optical sensor probe with side-viewing function to enable in-field visible-near infrared diffuse reflectance spectroscopy (VNIR-DRS) for soil. The optical probe consists of two microfabricated source chips and two collection chips. The source chips are used to deliver oblique (45 degrees) light incidence onto the soil surface, while the diffuse reflectance is received from the normal direction through the collector chips. Several design and fabrication considerations have been made to optimize the optical transmission efficiency of the probe and the signal-to-noise ratio (SNR) of the collected diffuse reflectance signal. The probe has a small outer dimension of 6 mm x 15 mm x 6 mm and thus can be easily fit into a typical soil penetrometer for in-filed VNIR-DRS measurements. Using the new optical probe, VNIR-DRS measurements have been successfully conducted on a number of soil samples, which shows the new optical probe offers better performance than the existing commercial ASD (R) 135680 bifurcated reflectance soil probe.