Tardías o Postquirúrgicas

Ocean-colour radiance is the wavelength-dependent solar energy captured by an optical sensor looking at the sea surface. The spectral distribution of the water-leaving radiance contains information on the ocean-

albedo and optical constituents of the seawater, in particular the concentration of the phytoplankton pigment chlorophyll-a (a proxy for phytoplankton biomass). Deriving ocean-colour products is not easy because the water-leaving radiance signal is relatively weak at the altitude of a satellite sensor (only 5-15 per cent of incident solar radiation, the remaining light having an atmospheric origin).

Ocean-colour radiometry (OCR) observations from space have revealed decadal-scale changes in the ocean biosphere. Passive ocean-colour sensors observe only the first (top) optical depth of the ocean (40- 60m in the open ocean to less than 1m in turbid coastal waters). However, when coupled with in situ

observations and numerical models, these space-based observations provide a three-dimensional understanding of ocean processes, their complexity, and their interactions with other parts of the Earth system. Therein, enhanced in situ sampling of ocean-colour and ecosystem variables is a requirement

and complement to satellite-based data.

The FCDR for ocean colour is the time series of calibrated TOA radiances, which are then corrected for the atmospheric contribution to the signal to obtain the water-leaving radiance suite, from which data products such as chlorophyll-a concentration are derived. The most important ocean-colour ECV products are the normalized water-leaving radiances and chlorophyll-a concentration. Other products are in development, such as coloured dissolved organic matter and particulate backscatter (used to estimate total suspended material). OCR products are the only measurements related to biological and biogeochemical processes in the ocean that can be routinely obtained at ocean-basin and global-ocean scales. These products are used to assess ocean ecosystem health and productivity, to understand the role of the oceans in the global carbon cycle, to manage living marine resources, and to quantify the impacts of climate variability and change.

The following is required for this ECV:

Product O.6.1 Ocean colour radiometry – water leaving radiance

Product O.6.2 Oceanic chlorophyll-a concentration derived from ocean colour radiometry Benefits

• Climate monitoring;

• Chlorophyll-a linked to carbon-cycling, including between the ocean and the atmosphere;

• Ecological indicators of the marine environment and mapping of marine ecological provinces. Target Requirements

Variable/ Parameter Horizontal Resolution

Vertical Resolution

Temporal

Resolution Accuracy Stability

Water Leaving Radiance 4km N/A Daily 5%* 0.5%

Chlorophyll-a concentration 30km N/A Weekly averages 30% 3%

*this 5% requirement is specifically for the blue and green wavelengths

Rationale: The rationale is based on values chosen to detect global and regional changes of a few percent in ocean chlorophyll cycles. The accuracy of 5 per cent for water leaving radiances for the blue and green wavelengths and 30 per cent for chlorophyll is intended for the concentration range 0.01-10 mg m-3 _{in waters in which chlorophyll-a dominates. These are termed Case-1 waters i.e., those whose} inherent optical properties can be adequately described by phytoplankton (represented by chlorophyll-a concentration), whereas Case-2 waters are optically complex water where additional in-water constituents considerably influence the optical variability. Four km horizontal resolution and a daily observing cycle are required at the global scale. For regional and coastal applications, 1km or smaller horizontal resolution is preferable. Stability of the OCR ECV has not yet been assessed. Several scientific papers have been published that show the trend in satellite derived chlorophyll concentration being on the order of +/- 2-3 per cent per year with maximums of +/- 5 per cent per year.

Currently achievable performance

• Accuracy: 5-15 per cent for water leaving radiances (Product O.6.1) (for the blue and green wavelengths) and 30-70 per cent for chlorophyll (Product O.6.2) in the concentration range 0.01-10 mg m-3 _{in Case 1 waters. For coastal waters and regional seas, which are typically Case 2, these} errors are considerably higher, typically on the order of 60-70 per cent for chlorophyll-a, but in areas

of extreme optical-complexity as high as 200-300 per cent. For these areas it is recommended that tailored algorithms be implemented;

• Spatial and temporal resolution: 4-9km horizontal resolution, daily, weekly and monthly observing cycles are available at global scale, dependent on sensor. For regional applications 1km horizontal resolution is available.

Requirements for satellite instruments and satellite datasets

FCDR of appropriate multispectral VIS imager radiances, derived from sensors with spectral and radiometric characteristics, which should be at a minimum of the same class as SeaWiFS, for example through:

• Sustained continuity of current provision of MODIS and MERIS-class, followed by development of a strategy based on advances beyond MODIS, MERIS and SeaWiFS-class capabilities;

• Future satellite observations with higher resolution and accuracy and more spectral bands from polar- orbiting and geostationary satellites; improved capability for ocean-colour observations in optically complex (e.g. coastal and turbid waters) and freshwater systems;

• Ancillary data required for ocean-colour radiances processing, including improved interpretation of sea-ice data from satellites; satellite measurement of salinity;

• Pixel-by-pixel uncertainty information attached to each measurement, where relevant (this is particularly relevant for the products derived from the water-leaving radiances, where large spatial differences are manifested).

Adequacy/inadequacy of current holdings

• Contributions to OCR ECV data records include current and commissioned polar-orbiting global OCR satellite missions, particularly SeaWiFS, MERIS on Envisat, MODIS-Aqua, OCM-2 on Oceansat-2, OLCI on Sentinel 3A and 3B, SGLI on GCOM-C, VIIRS on NPP and JPSS, as well as future NASA and CNES instruments under consideration; other instruments, such as China’s COCTS and Korea’s recently launched GOCI on geostationary or geosynchronous orbits, are also of considerable interest, and while these are not collecting global data, a constellation of ocean-colour radiometry on geostationary or geosynchronous platforms would be invaluable for addressing the aforementioned concerns in coastal and regional applications.

• There is no systematic consolidation of a global FCDR based on existing data from SeaWiFS, MODIS, and MERIS (although programmes in this direction have started – e.g. ESA CCI for OCR), and activities to address this need and to derive products should be encouraged; this requires cross- calibrated OCR from multiple satellites which should be merged to provide a data record of water- leaving radiances;

• Planned, next generation, OCR sensors (e.g. PACE and ACE) aim at achieving improved accuracy (i.e. < than 5 per cent for water-leaving radiance and 20 per cent for chlorophyll-a concentration); the OCR time series will undoubtedly benefit from this additional capability.

Calibration, validation and data archiving needs

• International coordination to establish an integrated network for sensor inter-comparison and uncertainty assessment for Ocean Colour Radiometry;

• Enhancement of the network of in situ measurements for calibration purposes, including appropriate

planning and coordination to improve the limited spatial coverage of in situ measurements;

• Continuation of support, by agencies, of bio-optical systems (e.g. MOBY, BOUSSOLE) for in situ data collection, to ensure appropriate vicarious calibration of spaceborne sensors;

• Enablement, by agencies, of the maintenance and expansion of in situ measurement networks (e.g.

AERONET-OC), providing standardized and spatially distributed time-series for the validation of OCR products;

• Promotion of the collection of comprehensive globally distributed in situ bio-optical (both inherent and

apparent) properties of sea-water constituents to support algorithm development and assessment;

• Harmonization of the methodologies and protocols for the vicarious calibration of OCR sensors;

• Promotion of the augmentation the Argo profiling drifter network to include the addition of sensors for observing the biological and light-field variables in the surface ocean (separate configurations should be implemented for validation purposes and to improve synoptic knowledge on the 3D structure of the ocean biology and biogeochemistry);

• Improvements in in situ platforms for observing the 3-D structure of the light field and biology/biogeochemistry in coastal regions, including improved ‘glider’ and mooring technology to provide a means of extrapolating the OC data through the water column;

• More international collaboration on establishing centralized data archive and distribution centres for in situ data, such as the SeaBASS and MERMAID systems;

• Further steps to strengthen OCR data stewardship activities for satellite OCR data record, including tools that provide easy access to multiple sources of satellite and in situ data (tools should also be

provided for the regular processing and analysis of combined datasets).

Immediate action, partnerships and international coordination

• Capitalizing on the OCR community benefits from several international bodies, the IOCCG, which provides the scientific basis and recommendations for advancing OCR science, and the OCR-Virtual Constellation, which provides the coordination for subsequent implementation;

• Revisiting of instrument calibration for historical OC sensors to improve consistency;

• Definition and implementation of an international initiative to establish an integrated network for sensor inter-comparison and uncertainty assessment for Ocean Colour Radiometry;

• Coordination, through user groups, of ocean-colour data such as IOCCP and CMIP and projects (e.g. CMUG and OC-CCI) and GEO initiatives such as SAFARI, ChloroGIN and Global Water Quality Tasks;

• Continuation of research on assimilation of ocean-colour products into ocean-climate models in order to improve carbon-cycle products such as pCO2 and air-sea CO2 fluxes;

• Implementation of plans for a sustained and continuous deployment of ocean-colour satellite sensors, together with research and analysis.

Link to GCOS Implementation Plan

• [IP-10 Action O15] Implement continuity of ocean colour radiance datasets through the plan for an

Ocean Colour Radiometry Virtual Constellation.

• [IP-10 Action O23] Establish a global network of long-term observation sites, covering all major ocean

habitats, and encourage collocation of physical, biological and ecological measurements.

Other applications

• Assimilation in ecosystem models for ecological state of the environment applications;

• Monitoring of the health and water quality of coastal seas (including the monitoring of harmful algal blooms).