Reflectometers for Absolute and Relative Reflectance Measurements in the Mid-IR Region at Vacuum

We demonstrated spectral reflectometers for two types of reflectances, absolute and relative, of diffusely reflecting surfaces in directional-hemispherical geometry. Both are built based on the integrating sphere method with a Fourier-transform infrared spectrometer operating in a vacuum. The third Taylor method is dedicated to the reflectometer for absolute reflectance, by which absolute spectral diffuse reflectance scales of homemade reference plates are realized. With the reflectometer for relative reflectance, we achieved spectral diffuse reflectance scales of various samples including concrete, polystyrene, and salt plates by comparing against the reference standards. We conducted ray-tracing simulations to quantify systematic uncertainties and evaluated the overall standard uncertainty to be 2.18% (k = 1) and 2.99% (k = 1) for the absolute and relative reflectance measurements, respectively.

The detection of Alternaria solani infection on tomatoes using ensemble learning

This paper presents a detection method of Alternaria solani in tomatoes. Several machine learning models were used to detect the pathogen, such as the implementation of decision trees and ensemble learning methods. The use of these methods requires the acquisition of large volumes of data and adequate preprocessing of this data. For the presented study the dataset of hyperspectral measurements of two varieties of tomatoes was used. Measurements were split into two groups: one inoculated with the Alternaria solani pathogen and the other one was treated as the reference. Measurements were taken by the spectroradiometer in consecutive measurement series. The main part of the study was the evaluation of the decision trees and the popular ensemble learning algorithms to select the most accurate one. After subsequent iterations of the training process and adjustment of hyperparameters, satisfactory accuracy results, equal to 0.987 for random forest, were obtained. This paper also covers the examination of the spectral range required for Alternaria solani identification. From several variants, the accuracy of models based on VIS and NIR spectral range was the closest to the accuracy obtained with the whole spectrum of measured absolute reflectance.

A simplified two layer model for light diffuse reflectance in thin skin fruits

A simple model of light diffuse reflectance in thin skin fruits is presented. The model is based in a semi-infinite two-layer geometry (skin and flesh) and introduces simplifications due to the fact that the first layer is very thin. The flesh is described in terms of the usual reduced scattering and absorption coefficients µs′ and µa but the skin is modeled by simple reflection (R), absorption (A) and transmission (T) coefficients. The problem of diffuse reflectance is thus reduced to the problem of determining the four constants µs′, µa, R and T. It is shown that the problem can be solved by using absolute reflectance and spatially resolved reflectance measurements simultaneously. The coefficients µs′ and µa are determined by the usual fit of the diffuse reflectance profile (photons re-emitted from the flesh far from the incidence point) to the diffusion approximation. The coefficients R and T are determined by a second fit involving the total reflectance profile (photons reemitted both from skin and flesh), the incident beam profile and the diffuse reflectance profile calculated according to the previously determined values of µs′ and µa. The anisotropy of the light re-emitted by the fruit can also be roughly compared with the Lambertian expected behavior. In order to test the model we have followed a population of 22 ‘Rocha’ pears along a period of two weeks. We have then performed the population averages along the time and checked the plausibility of the values obtained for µs′, µa, R and T according to the expected fruit physiological changes along ripening. The results show that all parameters are physically acceptable and evolve in time according to the expected fruit ripening physiology.