Development of a multichannel hyperspectral imaging probe for property and quality assessment of horticultural products

This paper reports on the development and calibration of a new multipurpose, multichannel hyperspectral imaging probe for property and quality assessment of horticultural and food products. The new multichannel probe consists of a 910 μm diameter fiber as a point light source and 30 light receiving fibers of three sizes (i.e., 50 μm, 105 μm and 200 μm) arranged in a symmetrical pattern, for simultaneous acquisition of 30 spatially-resolved reflectance spectra of horticultural and food samples with either flat or curved surface over the spectral region of 550-1650 nm. Three types of calibration for the multichannel probe were carried out, i.e., linearity calibrations for each fiber of the hyperspectral imaging system to ensure consistent linear responses of individual fibers, spectral response calibrations of individual fibers for each fiber size group and between the three groups of different size fibers, and optical property calibrations using four reference liquid samples. The calibration results showed that all 30 fibers had high linearity with exposure time with the coefficient of determination being greater than 0.990 for wavelengths greater than 700 nm; however, linear responses, as measured by the slope and intercept, for the individual fibers differed greatly and also varied with wavelength. After the calibrations, the probe was able to measure the scattering coefficient of the reference liquid samples with the relative errors between 3%-21%, whereas higher measurement errors were obtained for the absorption coefficient due to low absolute absorption values for the samples. Furthermore, the probe was demonstrated for measuring the absorption and scattering coefficients of tomato fruit at four maturity stages for the wavelengths of 550-1350 nm.