Calibration of a pushbroom hyperspectral imaging system for agricultural inspection

A method to calibrate a pushbroom hyperspectral imaging system has been demonstrated for use in agricultural inspection where the imaged object is close to the imaging system. The method consists of a modified geometric control point correction to remove smile and keystone effect from the system, and both wavelength and distance calibrations to reduce the wavelength and distance errors to less than 0.5 nm and 0.01 mm (across entrance slit-width), respectively. Next, a pixel-by-pixel percent reflectance calibration was performed at all wavelengths with dark current and 99% reflectance calibration-panel measurements, and results were verified with measurements on a certified gradient Spectralon panel with nominal values ranging from 12% to 99%. Results indicate that the method is capable of calibrating the hyperspectral system across the entire spectral range of the detector, but errors increase below 420 nm and above 840 nm. Further research should be performed to evaluate the stability of the calibration over time, and techniques must be developed to implement the calibration for real-time analysis.