Diffuse attenuation coefficient of downwelling irradiance: An evaluation of remote sensing methods.pdf

The propagation of downwelling irradiance at wavelength l from surface to a depth (z) in the ocean is governed by the diffuse attenuation coefficient, K(λ). There are two standard methods for the derivation of K(λ) in remote sensing, which both are based on empirical relationships involving the blue-to-green ratio of ocean color. Recently, a semianalytical method to derive K(λ) from reflectance has also been developed. In this study, using K(490) and K(443) as examples, we compare the K(λ) values derived from the three methods using data collected in three different regions that cover oceanic and coastal waters, with K(490) ranging from ~0.04 to 4.0 m⁻¹. The derived values are compared with the data calculated from in situ measurements of the vertical profiles of downwelling irradiance. The comparisons show that the two standard methods produced satisfactory estimates of K(λ) in oceanic waters where attenuation is relatively low but resulted in significant errors in coastal waters. The newly developed semianalytical method appears to have no such limitation as it performed well for both oceanic and coastal waters. For all data in this study the average of absolute percentage difference between the in situ measured and the semianalytically derived K is ~14% for λ = 490 nm and ~11% for λ = 443 nm

Immersion Factors for the RAMSES Series of Hyper-Spectral Underwater Radiometers

The immersion factors If of sample RAMSES radiance and irradiance hyper-spectral radiometers were experimentally determined in the 400-700 nm spectral range using state of the art protocols in view of supporting their use in accurate radiometric measurements for ocean color applications. Values of If obtained from the characterization of RAMSES-ACC-VIS irradiance units showed a dispersion of 2% in the blue increasing up to 4% in the red. Results obtained from the characterization of RAMSES-MRC-VIS radiance units having 20 degrees in-air full-angle field of view highlighted an average spectral bias of -2.4% in the theoretical If values determined with the sole use of the refractive indices of the medium and of the optical window. This average spectral bias exhibited values of -0.8% for the RAMSES-ARC-VIS radiometers having 7 degrees in-air full-angle-field of view. Using these results, reference If values have been proposed for the RAMSES series of radiometers.JRC.H.5-Rural, water and ecosystem resource

Empirical Model for Phycocyanin Concentration Estimation as an Indicator of Cyanobacterial Bloom in the Optically Complex Coastal Waters of the Baltic Sea

Commonly used parameters to assess cyanobacteria blooms are chlorophyll a concentration and cyanobacterial cell counts. Chlorophyll a is contained in all phytoplankton groups and therefore it is not a good estimator when only detection of cyanobacteria is desired. Moreover, laboratory determination of cyanobacterial cell counts is difficult and it requires a well-trained specialist. Instead of that, cyanobacterial blooms can be assessed using phycocyanin, a marker pigment for cyanobacteria, which shows a strong correlation with the biomass of cyanobacteria. The objective of this research is to develop a simple, remote sensing reflectance-based spectral band ratio model for the estimation of phycocyanin concentration, optimized for the waters of the Baltic Sea. The study was performed using hyperspectral remote sensing reflectance data and reference pigment concentration obtained in the optically complex coastal waters of the Baltic Sea, where cyanobacteria bloom occur regularly every summer, often causing severe damages. The presented two-band model shows good estimation results, with root-mean-square error (RMSE) 0.26 and determination coefficient (R2) 0.73. Moreover, no correlation with chlorophyll a concentration is observed, which makes it accurate in predicting cyanobacterial abundance in the presence of other chlorophyll-containing phytoplankton groups as well as for the waters with high colored dissolved organic matter (CDOM) concentration. The developed model was also adapted to spectral bands of the recently launched Sentinel-3 Ocean and Land Color Imager (OLCI) radiometer, and the estimation accuracy was comparable (RMSE = 0.28 and R2 = 0.69). The presented model allows frequent, large-scale monitoring of cyanobacteria biomass and it can be an effective tool for the monitoring and management of coastal regions

Diffuse Attenuation Coefficient of Downwelling Irradiance: An Evaluation of Remote Sensing Methods

The propagation of downwelling irradiance at wavelength λ from surface to a depth (z) in the ocean is governed by the diffuse attenuation coefficient, (λ). There are two standard methods for the derivation of (λ) in remote sensing, which both are based on empirical relationships involving the blue‐to‐green ratio of ocean color. Recently, a semianalytical method to derive (λ) from reflectance has also been developed. In this study, using (490) and (443) as examples, we compare the (λ) values derived from the three methods using data collected in three different regions that cover oceanic and coastal waters, with (490) ranging from ∼0.04 to 4.0 m−1. The derived values are compared with the data calculated from in situ measurements of the vertical profiles of downwelling irradiance. The comparisons show that the two standard methods produced satisfactory estimates of (λ) in oceanic waters where attenuation is relatively low but resulted in significant errors in coastal waters. The newly developed semianalytical method appears to have no such limitation as it performed well for both oceanic and coastal waters. For all data in this study the average of absolute percentage difference between the in situ measured and the semianalytically derived is ∼14% for λ = 490 nm and ∼11% for λ = 443 nm

Diffuse Attenuation Coefficient of Downwelling Irradiance: An Evaluation of Remote Sensing Methods

The propagation of downwelling irradiance at wavelength λ from surface to a depth (z) in the ocean is governed by the diffuse attenuation coefficient, (λ). There are two standard methods for the derivation of (λ) in remote sensing, which both are based on empirical relationships involving the blue‐to‐green ratio of ocean color. Recently, a semianalytical method to derive (λ) from reflectance has also been developed. In this study, using (490) and (443) as examples, we compare the (λ) values derived from the three methods using data collected in three different regions that cover oceanic and coastal waters, with (490) ranging from ∼0.04 to 4.0 m−1. The derived values are compared with the data calculated from in situ measurements of the vertical profiles of downwelling irradiance. The comparisons show that the two standard methods produced satisfactory estimates of (λ) in oceanic waters where attenuation is relatively low but resulted in significant errors in coastal waters. The newly developed semianalytical method appears to have no such limitation as it performed well for both oceanic and coastal waters. For all data in this study the average of absolute percentage difference between the in situ measured and the semianalytically derived is ∼14% for λ = 490 nm and ∼11% for λ = 443 nm

Remote Sensing of Shelf Sea Ecosystems - State of the Art and Perspectives

In 2005 the Marine Board - ESF established a Working Group (consisting of nominated experts) on remote sensing of shelf sea ecosystems, with a remit to review the state of the art and to make recommendations about research priorities and organisational changes needed to advance the application of scientific knowledge in this subject area. The context for the study is the increasingly urgent requirement for regular monitoring of shelf sea ecosystems in order to meet international treaty obligations for protecting the health status of European coastal waters, allied with a recognition that the contribution of ocean colour remote sensing to this operational task has been slow to develop when compared with the benefits of other satellite oceanography techniques in monitoring physical ocean properties. The report is written to inform those responsible for planning and funding marine science, remote sensing technology and the Earth Observation (EO) space programme, especially in relation to the development of operational oceanography capacity and capability in Europe. At the same time, the report aims to highlight to marine and optical scientists the intellectually challenging problems in this field which still need to be solved.JRC.H.3-Global environement monitorin

A study of episodic events in the Baltic Sea - combined in situ and satellite observations

A project was developed concerning the operational system of surveillanceand the recording of episodic events in the Baltic Sea.In situ information was to be combined with multi-sensory satelliteimagery to determine the extent of algal blooms, to track their evolutionand that of rapid environmental events like hydrological fronts. The mainelement of the system was an autonomous Ferry Box module on a ferry operatingbetween Gdynia and Karlskrona, automatically measuring temperature,salinity and chlorophyll <it>a</it> fluorescence. At pre-selected locations,discrete water samples were collected, which were subsequently analysedfor their phytoplankton content, and algal hepato- and neurotoxins;they were also used in toxicity tests with <it>Artemia franciscana</it>}