Exploring field-of-view non-uniformities produced by a hand-held spectroradiometer

Abstract

The shape of a spectroradiometer’s field of view (FOV) affects the way spectral measurements are acquired. Knowing this property is a prerequisite for the correct use of the spectrometer. If the substrate is heterogeneous, the ability to accurately know what is being measured depends on knowing the FOV location, shape, spectral and spatial sensitivity. The GER1500 is a hand-held spectrometer with a fixed lens light entry slit and has a laser guide that allows control over the target by positioning the entire unit. In the current study, the FOV of the GER1500 was mapped and analysed. The spectral and spatial non-uniformities of the FOV were examined and were found to be spectrally independent. The relationship between the FOV and the built-in laser guide was tested and found to have a linear displacement dependent on the distance to the target. This allows an accurate prediction of the actual FOV position.  A correction method to improve the agreement between the expected and measured reflectance over heterogeneous targets was developed and validated. The methods described are applicable and may be of use with other hand-held spectroradiometers.