Due to advances in optical technology a wide range of spectrometers is available. Recent interests in soil global libraries and sensor fusion presents a challenge with respect to combining data from different instrumentation. Only little research, however, has been done on the comparison of vis-NIRS sensors for soil characterization. There is a need for more work on the effects of scanning strategies, and use of different soil instrumentation. We compared three vis-NIR sensors with varying resolution, signal-to-noise ratios and spectral range. Their performance was evaluated based on soil organic carbon (SOC) and clay calibrations for 194 Danish top soils. Scanning procedures for the three spectrophotometers where done according to uniform laboratory protocols. SOC and clay calibrations were performed using PLS regression. One third of the data was used as an independent test set. A range of spectral preprocessing methods was applied in search for model improvement. Validation for SOC content using an independent data set derived from all three spectrophotometers provided values of RMSEP between 0.45 and 0.52 %, R2=0.44-0.58 and RPD=1.3-1.5. Clay content was predicted with a higher precision resulting in RMSEP values between 2.6-3.0 %, R2=0.70-0.77 and RPD values in the range from 2.1 to 2.5. No substantial differences in the prediction accuracy were found for the three sensors, although there was a tendency that in the tradeoff between noise and resolution, low noise was the more important for SOC and clay predictions. The application of different spectral preprocessing procedures did not generate important improvements of the calibration models either. The results from this study showed that as long as strict laboratory scanning protocols were followed no significant differences in constituent determination were found despite differences in spectral range, spectral resolution, spectral sampling intervals and sample presentation methods.
Journal of Near Infrared Spectroscopy, 2013, Vol 21, Issue 1, p. 67-80