Metadata Report for BODC Series Reference Number 1199771

• Metadata Summary

• Problem Reports

• Data Access Policy

• Narrative Documents

• Project Information

• Data Activity or Cruise Information

• Fixed Station Information

• BODC Quality Flags

• SeaDataNet Quality Flags

Metadata Summary

Problem Reports

No Problem Report Found in the Database

AMT Bio-Optics - Above-water radiance measurements (MicroSAS) Data Quality Report

Data was screened using the BODC in-house software, Edserplo.

During periods when the sun was less than 20° from the horizon the data has null flags 'N' applied. 'N' flags are also applied to any data considered outside the realms of possibility. 'M' flags were applied to any suspect data meeting the BODC data quality procedure. The data was sent as a final QC dataset received from the orginator. Flags were therefore only applied when deemed outside the data ranges or suspect.

Data Access Policy

Academic domain data

These data have no specific confidentiality restrictions for academic users. However, users must acknowledge data sources as it is not ethical to publish data without proper attribution. Any publication or other output resulting from usage of the data should include an acknowledgment.

The recommended acknowledgment is:

"This study uses data from data source/organisation/programme, provided by the British Oceanographic Data Centre and funded by the funding body."

Narrative Documents

Satlantic Surface Acquisition Systems (MicroSAS and HyperSAS)

The Satlantic Surface Acquisition System (SAS) is designed for above-water measurements of ocean colour using multispectral (MicroSAS) or hyperspectral (HyperSAS) digital optical sensors. Both the MicroSAS and the HyperSAS normally consist of two radiance and one irradiance sensor. One radiance sensor is pointed at the ocean and measures the sea surface signal, while the other is pointed at the sky and provides information for surface glint correction of the data acquired with the first sensor. The irradiance sensor is used to monitor the downwelling light field, which is required for computing remote sensing reflectance.

The MicroSAS uses the Satlantic OCR-500 series digital optical sensors. It has a sampling frequency of 20 Hz and provides spectral sampling of seven channels between 300 and 865nm for each of water radiance, sky radiance and irradiance. The HyperSAS uses the Satlantic OCR-3000 (MiniSpec) series digital optical sensors. It provides an increased spectral sampling of 136 channels between 350 and 800 nm at a lower and variable sampling rate.

SAS data may be used to derive concentrations of sea-water constituents, estimate estimate phytoplankton abundance and marine productivity, monitor organic pollution, calibrate and validate satellite ocean colour products. The system can be mounted on vessels or marine structures such as towers or platforms, and can also be used for aerial surveys.

Optional extras for the SAS include GPS units and a tilt and heading sensor to provide orientation, geo-referencing and accurate time information, and a radiation pyrometer for land or sea surface temperature measurements.

Specifications

*Special adapters can also be mounted to the MicroSAS radiometer to narrow the field of view to a half angle of 1.5° to 0.75°.

AMT Bio-Optics - Above Water Radiance Measurements (MicroSAS)

Data Acquisition and Analysis

In order to check the PIC algorithm performance, free of atmospheric error, total upwelling radiance, downwelling sky radiance and total downwelling irradiance were measured using a Satlantic SeaWiFS Aircraft Simulator (MicroSAS). The system consisted of a down-looking ocean radiance sensor and an up-looking sky-viewing radiance sensor, both mounted on the meteorological platform. The water-viewing radiance detector was set to view the ocean surface at 40° from nadir and the sky-viewing radiance sensor was set to view the sky 40° from the zenith (used in the correction for Fresnel reflectance) as recommended by Mueller et al. (2003b). The downwelling irradiance sensor was mounted high up to minimise shading from surrounding structures. Data from these sensors will be used to calculate spectral normalized water-leaving radiance (after filtering out white-caps and high pitch/roll anomalies) for comparison to the satellite estimates of normalized water-leaving radiance.

Sensors were rinsed regularly with Milli-Q water in order to remove salt deposits and any dust. The water radiance sensor was able to view over an azimuth range of ~180° across the ship's heading with no contamination from the ship's deck or wake. The direction of the sensor was adjusted constantly to view the water 120° from the sun's azimuth, to minimize sun glint. This was done using a computer-based system that calculated the sun's azimuth angle relative to the ship's heading and elevation constantly. The system used the ship's gyro-compass to determine the heading of the ship. Depending on the ship's course, the computer controlled a stepper motor that turned the sensors to the proper viewing angle. Protocols for operation and calibration were performed according to Mueller (Mueller et al. 2003a; Mueller et al. 2003b; Mueller et al. 2003c). Data were collected when the sun was above 20° elevation. Post-cruise, the 16Hz data was filtered to remove as much residual white cap and glint as possible. Calibrations with 10% reflectance plaque were performed during the cruise in order to assess the status of the radiometric calibrations. A factory calibration of the radiometers was performed before the cruise.

Reference:

Mueller J.L., Austin R.W., Morel A., Fargion G.S., McClain C.R. 2003a. Ocean optics protocols for satellite ocean color sensor validation, Revision 4, Volume I: Introduction, background, and conventions. Greenbelt, MD: Goddard Space Flight Center. 50 p.

Mueller J.L., Morel A., Frouin R., Davis C., Arnone R., Carder K., Lee Z.P., Steward R.G., Hooker S.B., Mobley C.D., McLean S., Holben B., Miller M., Pietras C., Knobelspiesse K.D., Fargion G.S., Porter J., Voss K. 2003b. Ocean optics protocols for satellite ocean color sensor validation, Revision 4, Volume III: Radiometric measurements and data analysis protocols. Greenbelt, MD: Goddard Space Flight Center. 78 p.

Mueller J.L., Pietras C., Hooker S.B., Austin R.W., Miller M., Knobelspiesse K.D., Frouin R., Holben B., Voss K. 2003c. Ocean optics protocols for satellite ocean color sensor validation, Revision 4, Volume II: Instrument specifications, characterisation and calibration. Greenbelt, MD: Goddard Space Flight Center.

BODC Data Processing Procedures

Data were submitted to BODC as a .out file, which was then saved to the archive following the relevant BODC transfer procedure:

The files were provided to BODC containing MicroSAS radiance parameters at seven different wavelengths. Temperature, salinity and chlorophyll-a from sea surface water taken from the ship's non-toxic water supply and these were banked separately. Additional metadata was supplied including: cruise, latitude, longitude, date.

The data were converted from the comma delimited SeaBass format into BODC internal format using the relevant BODC transfer function.

Parameter codes defined in BODC parameter dictionary were assigned to the variables as shown in the table below. Unit conversions were necessary for downwelling irradiance which was provided in µW cm^-2 nm and were converted to µW mm^-2 nm. The units for the other radiance parameters were provided in µW cm^-2 nm sr and were converted to µW m^-2 nm sr.

Parameter Mapping Table

Screening

Once transferred the reformatted data were imported into the BODC in-house visualisation software, Edserplo. Data were appropriately flagged and double checked for any anomalous results. This was completed according to BODC procedures.

AMT Bio-Optics Instrumentation - Above-water Radiance Measurements (MicroSAS)

Project Information

Oceans 2025 Theme 10, Sustained Observation Activity 1: The Atlantic Meridional Transect (AMT)

The Atlantic Meridional Transect has been operational since 1995 and through the Oceans 2025 programme secures funding for a further five cruises during the period 2007-2012. The AMT programme began in 1995 utilising the passage of the RRS James Clark Ross between the UK and the Falkland Islands southwards in September and northwards in April each year. Prior to Oceans 2025 the AMT programme has completed 18 cruises following this transect in the Atlantic Ocean. This sustained observing system aims to provide basin-scale understanding of the distribution of planktonic communities, their nutrient turnover and biogenic export in the context of hydrographic and biogeochemical provinces of the North and South Atlantic Oceans.

The Atlantic Meridional Transect Programme is an open ocean in situ observing system that will:

• give early warning of any fundamental change in Atlantic ecosystem functionng
• improve forecasts of the future ocean state and associated socio-economic impacts
• provide a "contextual" logistical and scientific infrastructure for independently-funded national and international open ocean biogeochemical and ecological research.

The specific objectives are:

• To collect hydrographic, chemical, ecological and optical data on transects between the UK and the Falkland Islands
• To quantify the nature and causes of ecological and biogeochemical variability in planktonic ecosystems
• To assess the effects of variability in planktonic ecosystems on biogenic export and on air-sea exchange of radiatively active gases

The measurements taken and experiments carried out on the AMT cruises will be closely linked to Themes 2 and 5. The planned cruise track also allows for the AMT data to be used in providing spatial context to the Sustained Observation Activities at the Porcupine Abyssal Plain Ocean Observatory (SO2) and the Western Channel Observatory (SO10).

More detailed information on this Work Package is available at pages 6 - 9 of the official Oceans 2025 Theme 10 document: Oceans 2025 Theme 10

Weblink: http://www.oceans2025.org/

Data Activity or Cruise Information

Cruise

Complete Cruise Metadata Report is available here

Fixed Station Information

No Fixed Station Information held for the Series

BODC Quality Control Flags

The following single character qualifying flags may be associated with one or more individual parameters with a data cycle:

SeaDataNet Quality Control Flags

The following single character qualifying flags may be associated with one or more individual parameters with a data cycle: