Feasibility Study of NIR Diffuse Optical Tomography on Agricultural Produce

E.K. Kemsley1, H.S. Tapp1, R. Binns 3, R.O. Mackin3 and A.J. Peyton2

1 Institute of Food Research, Norwich Research Park, Colney, Norwich, NR4 7UA, UK

2 University of Manchester, School of Electrical & Electronic Engineering, Manchester, M60 1QD, UK

3 Lancaster University, Engineering Department, LA1 4YR, UK Email: henri.tapp@bbsrc.ac.uk

ABSTRACT

Background: Monitoring the quality of fresh fruit and vegetables benefits both the producer, by offering a competitive advantage, and consumers, by improving consistency and hence encouraging a more healthy and varied diet. Near infrared (NIR) spectroscopy is a candidate technology for monitoring agricultural produce quality. Here there has been a recent trend toward transmission- based geometries which interrogates deeper into the sample. NIR tomography is the natural progression of this, offering the possibility of detecting internal defects.

Objective: To evaluate a NIR tomograph built from relatively low-cost components.

Design: The tomograph comprised a stabilised VIS/NIR broadband source; a diode-array NIR spectrometer and a sample turn-table. The angular positions of the detector and turn-table could be moved independently of each other using two stepper motors under computer control. An experimental approach was adopted to generate a linear ‘difference image’ reconstruction matrix using 47 mm diameter potato cores and a 10 mm diameter black rod acting as an absorbing perturbation. The reconstruction matrix was generated using multiple linear regression and evaluated for the case of two perturbing rods.

Results: It was possible to produce images of a comparable quality to other soft-field tomographic techniques.

Conclusions: Although conducted under highly simplified conditions, the results suggest NIR tomography has potential for monitoring internal defects in agricultural produce.

Keywords Quality Control, Near-infrared, Food, Optical Tomography, Difference Imaging