Development of a compound-eye spectrometer for calibration-transfer-free spectroscopy

This study examined a novel "compound-eye spectrometer" concept to reduce instrument differences in near-infrared (NIR) spectroscopy, and eliminate the requirement for complex calibration transfer (CT) procedures. NIR spectroscopy, which is a rapid, nondestructive, and cost-effective technique, faces challenges in its wider application owing to the variations in spectral data caused by instrumentation differences. Such variations require the use of CT, which is time-consuming and labor-intensive. A custom-built compound-eye spectrometer was developed by integrating 16 micro-electro-mechanical system (MEMS) spectral sensors arranged in a circle to function as a virtual spectrometer. The objective was to minimize the impact of individual sensor variations by averaging signals from multiple sensors, thereby improving the sensitivity and potentially enabling CT-free spectroscopy. Calibration models were developed for sucrose solutions in the concentration range of 0-30 wt% using the developed compound-eye spectrometer and three commercially available reference spectrometers. When a calibration curve from a single spectrometer was shared with other spectrometers to predict the sucrose concentrations, the virtual spectrometers composed of five MEMS spectral sensors demonstrated superior performance, with a significantly smaller absolute bias and root mean squared error of prediction compared to the reference instruments. This was attributed to the lower variation in absorbance at the Brix-correlated wavelengths in the compound-eye spectrometer. Although limitations (measurement noise and performance variations) require further investigation, the compound-eye spectrometer concept holds the potential for developing CT-free spectroscopy. Future work will involve evaluating the applicability of this concept to fruit and vegetable samples measured using compound-eye spectrometers on different bodies.