In situ determination of the remote sensing reflectance: an inter-comparison

Abstract

Abstract. Inter-comparison of data products from simultaneous measurements performed with independent systems and methods is a viable approach to assess the consistency of data and additionally to investigate uncertainties. Within such a context the inter-comparison called Assessment of In Situ Radiometric Capabilities for Coastal Water Remote Sensing Applications (ARC) was carried out at the Acqua Alta Oceanographic Tower in the northern Adriatic Sea to explore the accuracy of in situ data products from various in-and above-water optical systems and methods. Measurements were performed under almost ideal conditions, including a stable deployment platform, clear sky, relatively low sun zenith angles and moderately low sea state. Additionally, all optical sensors involved in the experiment were inter-calibrated through absolute radiometric calibration performed with the same standards and methods. Inter-compared data products include spectral waterleaving radiance L w (λ), above-water downward irradiance E d (0 + ,λ) and remote sensing reflectance R rs (λ). Data products from the various measurement systems/methods were directly compared to those from a single reference system/method. Results for R rs (λ) indicate spectrally averaged values of relative differences comprised between −1 and +6 %, while spectrally averaged values of absolute differences vary from approximately 6 % for the above-water systems/methods to 9 % for buoy-based systems/methods. The agreement between R rs (λ) spectral relative differences and estimates of combined uncertainties of the inter-compared systems/methods is noteworthy.

The Potential of Autonomous Ship-Borne Hyperspectral Radiometers for the Validation of Ocean Color Radiometry Data

“…Some of the differences observed in the blue region between the DALEC R rs and the satellite R rs may be further reduced by using data processing methods based on spectrally variant ρ (e.g., Lee, Ahn, Mobley and Arnone [22]). This study did not include an investigation and quantification of each source of uncertainty in the estimate of the DALEC R rs , such analysis of the uncertainty budget would include the effects on uncertainty of the system calibration, the superstructure perturbations, viewing geometries, distance of the instrument footprint from the hull, estimate of W, ρ and , non-cosine response of E d and further environmental perturbation such as wave effects [4,6,12].…”

“…The aboveand in-water approaches to determine R rs rely on radiometric measurements analysed with different underlying assumptions: (i) in-water radiometry enables the determination of immediately below surface radiometric quantities based on the extrapolation of subsurface continuous or fixed-depth profiles of radiometric quantities [5,7,12]; (ii) above-water systems operate with non-nadir viewing geometry and can be corrected for the skylight reflected into the field-of-view by the air-sea interface [5,6,12,13].…”

Methods in reducing surface reflected glint for shipborne above-water remote sensing

“…To better approximate R RS these parameters have to be observed with high accuracy and precision. With time and usage instruments demand routine calibration and sometimes their sensitivity or detection capabilities become depleted due to lifespan of sensors, superstructure perturbations, or improper use [15,25,26].…”

MOD2SEA: A Coupled Atmosphere-Hydro-Optical Model for the Retrieval of Chlorophyll-a from Remote Sensing Observations in Complex Turbid Waters

“…Accurate estimation of water-leaving reflectance from satellite sensors is a fundamental goal for ocean color satellite missions [83]. Basically, the commonly applied atmospheric correction methods based on zero water-leaving reflectance in the near-infrared bands fail when applied to turbid waters since the high concentrations of water constituents lead to a detectable water-leaving reflectance in the near-infrared region in satellite image.…”