IMIS

This dataset contains autonomously acquired abovewater PANTHYR water reflectance data from a pair of TriOS RAMSES radiance and irradiance sensors. Measurements are performed under a sun-sensor geometry that minimises sun and sky glint on the air-water interface, as recommended by Mobley (1999), and utilised commonly in above water measurements, e.g. by Ruddick et al. (2006). Irradiance and radiance measurements are made sequentially rather than simultaneously, with a full cycle containing 3 irradiance (Ed), 3 downwelling radiance (Ld), 11 upwelling radiance (Lu), 3 more Ld and 3 more Ed. This sequence takes about 1 minute to complete in normal illumination conditions, and temporal stability checks are performed on these sequential measurements (Vanhellemont 2020). A given number of valid measurements (Ed: 5/6, Ld: 5/6, Lu: 9/11) are required for further processing. RAMSES data are resampled to a common wavelength grid between 355 and 945 nm with a 2.5 nm step. A "Fresnel" correction for the air-water interface reflectance is performed using the Mobley (1999) LUT for a fixed (2 m/s) or modeled (NCEP) wind speed. Full details on the PANTHYR system are provided in Vansteenwegen et al. 2019. This dataset contains the average and standard deviation of hyperspectral irradiance (ed), downwelling radiance (ld), total upwelling radiance (lu), and derived water-leaving radiance (lw). Water-leaving radiance reflectance is provided with NIR similarity spectrum correction (rhow) and without NIR similarity spectrum correction (rhow_nosc). Data passed automated quality control but have not been screened by an expert.

The general objective of the HYPERMAQ project was to develop and test new algorithms for aquatic remote sensing of coastal and inland waters, using both hyperspectral and high resolution multispectral satellite data to provide more than “just” concentration of suspended particulate matter and chlorophyll. Test sites focused particularly on turbid waters. The PANTHYR (pan-and-tilt hyperspectral radiometer system) was designed in HYPERMAQ for autonomous measurement of hyperspectral water reflectance for the validation of satellite reflectance in visible and near-infrared bands (400–900 nm).