Advances in the Ocean Color Component of the Aerosol Robotic Network (AERONET-OC)

Abstract

The Ocean Color component of the Aerosol Robotic Network (AERONET-OC) supports ocean color related activities such as validation of satellite data products, assessment of atmospheric correction schemes and evaluation of bio-optical models, through globally distributed standardized measurements of water-leaving radiance and aerosol optical depth. In view of duly assisting the AERONET-OC data user community, this work: i. summarizes the latest investigations on a number of scientific issues related to above-water radiometry; ii. emphasizes the network expansion that from 2002 till the end of 2020 integrated 31 effective measurement sites; iii. shows the equivalence of data product accuracy across sites and time for measurements performed with different instrument series; iv. illustrates the variety of water types represented by the network sites ensuring validation activities across a diversity of observation conditions; and v. finally documents the availability of water-leaving radiance data corrected for bidirectional effects applying a method specifically developed for chlorophyll-a dominated waters and an alternative one likely suitable for any water type.

Phytoplankton Bloom Dynamics in the Baltic Sea Using a Consistently Reprocessed Time Series of Multi-Sensor Reflectance and Novel Chlorophyll-a Retrievals

“…It should be noted that these global match-ups were based on disparate instrumentation and quality standards [12,83] featuring lower accuracy in comparison to the AERONET-OC data used as a reference in this study [84]. The satisfactory performance in the 490-670 nm spectral range and the lower accuracy reported for the blue spectral bands confirm the findings with other radiometric validation exercises carried out in the Baltic Sea [24,[32][33][34]42,64,65]. Specifically, the observed bias values for R rs (555) and R rs (670) (8.33 × 10 −5 and 1.36 × 10 −4 sr −1 , respectively) were an order of magnitude lower than the thresholds defined in [78] (i.e., 4.25 × 10 −3 and 1.22 × 10 −3 sr −1 for the 555 and 670 nm bands, respectively).…”

“…This study presented recent improvements for the 1997-2019 Chl-a time series determined for the Baltic Sea from space-borne multi-sensor data. The accuracy of OC-CCI R rs for the Baltic Sea was assessed with AERONET-OC data acquired from 2005 to 2019 at three sites located in different sub-basins [64][65][66]. In agreement with other studies [64,65], results from the analysis of R rs match-up data showed that the external bands (412 and 670 nm) are affected by larger uncertainties: R rs (412) was characterized by a high dispersion, while R rs (670) had the largest bias.…”

“…The accuracy of OC-CCI R rs for the Baltic Sea was assessed with AERONET-OC data acquired from 2005 to 2019 at three sites located in different sub-basins [64][65][66]. In agreement with other studies [64,65], results from the analysis of R rs match-up data showed that the external bands (412 and 670 nm) are affected by larger uncertainties: R rs (412) was characterized by a high dispersion, while R rs (670) had the largest bias. The OC-CCI R rs were deemed adequate for the detection of summer surface blooms as the observed bias values for R rs (555) and R rs (670) were an order of magnitude lower than the adopted thresholds.…”

“…Reference data for the assessment of space-borne R rs spectral values were derived from field measurements acquired by the Aerosol Robotic Network-Ocean Color (AERONET-OC) at three sites in the Baltic Sea [64][65][66] (Figure 1). Data acquired between 2005 and 2019 from the Gustav Dalen Tower (58.594 • N, 17.467 • E), the Helsinki Lighthouse (59.949 • N, 24.925 • E), and the Irbe Lighthouse (57.751 • N, 21.723 • E) were used for independent validation.…”

“…Data acquired between 2005 and 2019 from the Gustav Dalen Tower (58.594 • N, 17.467 • E), the Helsinki Lighthouse (59.949 • N, 24.925 • E), and the Irbe Lighthouse (57.751 • N, 21.723 • E) were used for independent validation. Specifically, AERONET-OC Level-2 measurements of normalized water-leaving radiance, L wN , corrected for bi-directional effects and quality-controlled as part of the operational data processing [64][65][66], were divided by the extra-solar irradiance spectrum to calculate the in situ R rs [67]. These data were then band-shifted to the CCI spectral wavelengths by means of inverse and direct application of the QAA algorithm [54][55][56].…”