Calibration verification of an underwater hyperspectral imaging push broom instrument to measure light in absolute units and field demonstration

The push broom design of an underwater hyperspectral imaging (UHI) instrument makes it possible to measure angle-resolved spectral radiance L(λ) in a plane. We describe the characterization of a commercial UHI instrument (UHI-4, Ecotone AS, Norway) and the spectral, geometric, and radiometric calibration transfer for measuring L(λ) in absolute units [µWcm−2nm−1sr−1]. We present a low-cost instrument characterization approach that is intended to be easily replicated for other users to perform their own calibration transfer. Cross-calibration with a RAMSES-ARC spectroradiometer (TriOS, Germany) in air and in water shows good linear correlation across the observed spectral range and over four orders of magnitude in dynamic range, with the UHI instrument providing higher sensitivity overall.