The implications of non-uniformity in fields-of-view of commonly used field spectroradiometers

Accurately determining the field-of-view (FOV) is a basic requirement in photogrammetry and imaging spectroscopy but has rarely been considered in detail in field spectroscopy where the specifications for different spectroradiometers generally lack clarity or detail. The issue can be further compounded with full spectral systems (0.4 to 2.5 mum) which include multiple spectrometers; in these systems the size and alignment of the viewing optics may cause significant spectral non-uniformity across the theoretical measurement area. When recording spectra from heterogeneous targets it is important to have the FOV accurately defined because distinct reflecting surfaces may be present in varying proportions. We assessed the FOVs of the analytical spectral devices field spec pro FR and spectra Vista Corporation GER 3700 spectroradiometers. The resulting directional response functions are plotted, highlighting several areas of concern.