Abstract
Near-infrared spectroscopy (NIRS) is widely used in fruit and vegetable quality evaluations, usually after harvesting. In particular, the moisture content is a key parameter for determining product quality; processing phase, e.g., drying process; and economical value. NIRS methods are well-established for laboratory practices where the specimens are properly prepared and measurement conditions are well controlled. On the other hand, it is known that in-field NIRS measurements present several difficulties, as many influencing variables, such as mechanical vibrations, electrical and optical disturbances, and dust or dirt in general, can affect the spectral measurement. In this paper, we propose the design and present the prototype of a NIRS-based measuring system for the rapid determination of the moisture content of bales. The new system uses of a halogen lamp illumination unit to recover water absorption spectral data in the range of 900–1700 nm. The compact stainless steel body makes the instrument portable and easy to transport for rapid in-field MC measurements. The prototype system was characterized and its performance extensively evaluated in a laboratory environment. Finally, a preliminary test was carried out, where the moisture contents of 12 freshly harvested crops samples were measured using the partial least squares (PLSs) regression method. The obtained results show that our prototype system can estimate the alfalfa moisture content information with a coefficient of determination R2 of 0.985 and a root mean square relative error of estimation of 7.1%.
Highlights
It is known that in-field Near-infrared spectroscopy (NIRS) measurements present several difficulties, as many influencing variables, such as mechanical vibrations, electrical and optical disturbances, and dust or dirt in general, can affect the spectral measurement
As discussed in our previous paper [7], we propose to extract the information on moisture content (MC) by analyzing the NIR absorption spectrum in in a properly selected band of interest (BOI) ∈ [1.37 μm, 1.55 μm] where the maximum correlation with the MC contents and the least correlation with the density of the collected samples is achieved
On the side opposite the optical window, the flap houses a sheet of white paper, i.e., the reflectance reference target (RRT), whose reflectivity has been determined by comparison with National Institute of Standards and Technology (NIST) certified reflectance standards (Spectralon® Diffuse Reflectance Standards, LABSPHERE©Inc., North Sutton, NH, USA)
Summary
Great efforts have been made for the research and development of techniques that allow the evaluation of the physical properties of agricultural products [1]. Two techniques offer the potential to perform MC measurements without contact: (i) microwave attenuation [1] and (ii) near-infrared spectroscopy (NIRS) [1,4,5]. In the paper by Cassanelli et al, we tested the feasibility of our approach in our laboratory using an integrating sphere and other standard laboratory equipment After this phase, we designed and realized the prototype for the in-field crop moisture measurements described in this paper. Numerous physical quantities, e.g., crop density [8], can affect the relationship between MC and the near-infrared (NIR) spectrum, especially when measurements are performed in harsh and uncontrolled conditions. As discussed in our previous papers [7,8], a robust statistical analysis can help to recover the information of interest, even with the presence of different densities or leafstem ratios in the sample.
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