Comment on "Long Island Sound Coastal Observatory: assessment of above-water radiometric measurement uncertainties using collocated multi and hyperspectral systems".
Harmel et al. [Appl. Opt.50, 5842 (2011)] presented an intercomparison of products from collocated above-water radiometric measurements performed with a Hyperspectral Surface Acquisition System (HyperSAS) and a multispectral Sea-viewing Wide Field of View Sensor Photometer Revision for Incident Surface Measurements (SeaPRISM). Radiometric products from HyperSAS data were determined with a processing code written by the authors, while products from SeaPRISM measurements were obtained with the standard processor of the Ocean Color component of the Aerosol Robotic Network (AERONET-OC). Despite the application of equivalent processing schemes, results exhibit spectrally averaged unbiased relative differences of +26% between HyperSAS and SeaPRISM exact normalized water leaving radiances, L(WN). Harmel et al. concluded that the sun-glint correction scheme applied for SeaPRISM data reduction is a major reason for the observed differences. This comment rejects the former conclusion as being supported by a wrong interpretation of the AERONET-OC processing scheme, and a consequent failure in describing the spectral properties of the glint radiance determined from SeaPRISM data. Afterward, the differences between HyperSAS and SeaPRISM L(WN) reported by Harmel et al. are challenged with intercomparison results from collocated measurements periodically performed over almost a decade with an in-water multispectral system and SeaPRISM. Results for L(WN) from the in-water system show spectrally averaged unbiased relative differences of +1% with respect to SeaPRISM values.
Joint Research Centre, Institute for Environment and Sustainability, Ispra, Italy. Giuseppe.zibordi@jrc.it
Giuseppe
G
Zibordi