James Fishwick

Validation of MERIS reflectance and chlorophyll during the BENCAL cruise October 2002: preliminary validation of new demonstration products for phytoplankton functional types and photosynthetic parameters

We measured water leaving reflectance, phytoplankton pigments, optical properties and photosynthetic parameters in the southern Benguela ecosystem in October 2002. These data were used to validate MERIS standard products: reflectance (MERIS wavelengths) and Case 1 Chlorophyll‐a. In this heterogeneous area, accurate validation required sampling within a few minutes of the satellite overpass. Inter‐pigment relationships e.g. Total Chlorophyll (TChla) to Total Pigment (TP) were robust (R2∼0.99) yet pigment ratios (TChla/TP) were not constant (range 0.44 to 0.62) increasing log‐linearly with biomass (R2∼0.7). Photosynthetic parameters (e.g. Photosynthetic Quantum Efficiency, PQE) and optical ratios (a676/a440) also increased log‐linearly with biomass (R2∼0.8). PQE, pigment and optical ratios were linearly inter‐correlated (R2∼0.7 to 0.8). From these data we derived the bio‐optical traits for several phytoplankton functional types (PFTs): micro‐plankton (diatoms and dinoflagellates) had high biomass, pigment ratios and PQE; nano‐flagellates had low to intermediate biomass, pigment ratios and PQE; prokaryotes had very low biomass, pigment ratios and PQE. We present MERIS data analysed for PFTs and new products (PQE).

Functional relationships and bio-optical properties derived from phytoplankton pigments, optical and photosynthetic parameters; a case study of the Benguela ecosystem

The relationships between phytoplankton pigments, optical properties and photosynthetic parameters for different phytoplankton functional types (derived by diagnostic pigment indices, DPI) were determined from data acquired in the Benguela ecosystem and the offshore region in October 2002. We observed robust inter-pigment relationships: total chlorophyll-a (TChla) was highly correlated with total pigment (TP) and accessory pigment (AP). However, the regression equations for stations dominated by flagellates differed from the equations for stations dominated by diatoms and dinoflagellates. The pigment ratio TChla/TP and the optical ratio a676/a440 were not constant but increased non-linearly with increasing TChla or TP; complimentarily the AP/TP and a490/a676 ratios decreased. There were significant non linear relationships between the photosynthetic parameters F v /F m or σ PSII measured by Fast Repetition Rate Fluorometry and TChla orTP. Pigment ratios, optical ratios, F v /F m and σ PSII were all inter-correlated with high significance. We determined the distinctive bio-optical properties associated with dominant phytoplankton functional types (derived by DPI) that conformed to the classical partitioning: flagellates (nano-plankton, comprising several taxa) had low biomass, low TChla/TP fraction and low F v /F m and high σ PSII ; diatoms and dinoflagellates (micro-plankton) had high biomass, pigment ratios, F v /F m and low σ PSII .

Relationship between the distribution function of ocean nadir radiance and inherent optical properties for oceanic waters

The distribution function of the ocean nadir radiance, defined by the upward radiance-to-irradiance ratio, is investigated as functions of the absorption coefficient and the volume scattering function to understand their relationship rather than to develop a numerical algorithm. It is shown for oceanic waters that the distribution function is directly proportional to the volume scattering function normalized by the backscattering coefficient. The relatively small spectral variation of the distribution function is explained by the small spectral variation of the normalized volume scattering function, as well as by a function that describes the contribution of the backscattering-to-absorption ratio to the distribution function. The interpretation described was verified against in situ data, highlighting factors controlling the distribution function of oceanic waters.

Technology, Design, and Operation of an Autonomous Buoy System in the Western English Channel

Abstract A buoy system has been developed to continually monitor the operationally demanding coastal and open-shelf environment of the western English Channel. The buoys measure a range of physical and biogeochemical parameters on an hourly basis at two established long-term monitoring sites and the data are relayed to shore in near–real time using radio communications. This paper describes the technological challenges faced in such long-term marine deployments including the mooring design, warning systems, command and control, and radio communications, and how each were overcome. The fine temporal frequency data are used within an operational oceanography context, will underpin the long-term sustained observations in the western English Channel, and will form the basis of improvements to finescale ecosystem modeling to better predict any changes in the U.K. shelf seas.

Evaluating Operational AVHRR Sea Surface Temperature Data at the Coastline Using Benthic Temperature Loggers

The nearshore coastal ocean is one of the most dynamic and biologically productive regions on our planet, supporting a wide range of ecosystem services. It is also one of the most vulnerable regions, increasingly exposed to anthropogenic pressure. In the context of climate change, monitoring changes in nearshore coastal waters requires systematic and sustained observations of key essential climate variables (ECV), one of which is sea surface temperature (SST). As temperature influences physical, chemical and biological processes within coastal systems, accurate monitoring is crucial for detecting change. SST is an ECV that can be measured systematically from satellites. Yet, owing to a lack of adequate in situ data, the accuracy and precision of satellite SST at the coastline are not well known. In a prior study, we attempted to address this by taking advantage of in situ SST measurements collected by a group of surfers. Here, we make use of a three year time-series (2014–2017) of in situ water temperature measurements collected using a temperature logger (recording every 30 min) deployed within a kelp forest (∼3 m below chart datum) at a subtidal rocky reef site near Plymouth, UK. We compared the temperature measurements with three other independent in situ SST datasets in the region, from two autonomous buoys located ∼7 km and ∼33 km from the coastline, and from a group of surfers at two beaches near the kelp site. The three datasets showed good agreement, with discrepancies consistent with the spatial separation of the sites. The in situ SST measurements collected from the kelp site and the two autonomous buoys were matched with operational Advanced Very High Resolution Radiometer (AVHRR) EO SST passes, all within 1 h of the in situ data. By extracting data from the closest satellite pixel to the three sites, we observed a significant reduction in the performance of AVHRR at retrieving SST at the coastline, with root mean square differences at the kelp site over twice that observed at the two offshore buoys. Comparing the in situ water temperature data with pixels surrounding the kelp site revealed the performance of the satellite data improves when moving two to three pixels offshore and that this improvement was better when using an SST algorithm that treats each pixel independently in the retrieval process. At the three sites, we related differences between satellite and in situ SST data with a suite of atmospheric variables, collected from a nearby atmospheric observatory, and a high temporal resolution land surface temperature (LST) dataset. We found that differences between satellite and in situ SST at the coastline (kelp site) were well correlated with LST and solar zenith angle; implying contamination of the pixel by land is the principal cause of these larger differences at the coastline, as opposed to issues with atmospheric correction. This contamination could be either from land directly within the pixel, potentially impacted by errors in geo-location, or possibly through thermal adjacency effects. Our results demonstrate the value of using benthic temperature loggers for evaluating satellite SST data in coastal regions, and highlight issues with retrievals at the coastline that may inform future improvements in operational products.