Integrated fiber optic spectrally resolved downwelling irradiance sensor for pushbroom spectrometers.

We present an integrated fiber optic spectrally resolved downwelling irradiance sensor for pushbroom hyperspectral imagers. The system comprises of a cosine corrector and custom fiber patch cables, collecting the ambient light in a large solid angle and feeding it directly to the entrance slit of the spectrometer. The system enables simultaneous measurement of downwelling and upwelling irradiance using the main hyperspectral camera sensor. As a demonstration, the spectral reflectance of a soil sample was measured with a RMSE of 8.4%, a significant improvement on the RMSE of 54% found without correction. At a weight of approximately 10 grams, this system provides a substantial weight saving over standalone incident light sensing instruments.