GlobColour
Products Description

Merging methods

Format

Input data sensors

Product User Guide

GlobColour Products Description

Introduction

One objective of GlobColour is to produce a long time series (10 years) of ocean color data merged from four satellite data sources:

• the Medium Resolution Imaging Spectrometer Instrument (MERIS) aboard ENVISAT,
• the Moderate Imaging Spectrometer (MODIS) on the Aqua Earth Observing System (EOS) mission,
• the Sea-viewing Wide Field of view Sensor (SeaWiFS) on board OrbView-2,

The parameters distributed to the end-users are:

• Chlorophyll-a, case I water(CHL₁)
• Chlorophyll-a, case II water (CHL₂)
• Total Suspended Matter (TSM)
• Coloured dissolved and detrital organic materials (CDM)
• Particulate back-scattering coefficient (b_bp)
• Diffuse attenuation coefficient (Kd(490))
• Fully normalised water leaving radiances at 412, 443, 490, 510, 531, 550-565, 620, 665-670 nm (Lxxx)
• Water leaving radiances at 681 and 709 nm (Lxxx)
• Relative excess of radiance at 555 nm (EL555)
• Aerosol optical thickness over water (T865)
• Cloud Fraction (CF)

Two spatial domains are covered:

• the global Earth domain.
• local Diagnostic Data Sets areas (DDS).

Products are generated for two merging techniques:

• weighted averaging
• GSM model

The following table summarizes which parameters are available.

Parameter	Description	L3 merging method	M
CHL1	chlorophyll-a concentration (mg/m3) for case 1 water	weighted averaging method + GSM model
CHL2	chlorophyll-a concentration (mg/m3) for case 2 water	weighted averaging method
TSM	total suspended matter concentration (g/m3)	weighted averaging method
CDM	Coloured dissolved and detrital organic materials (m-1)	weighted averaging method + GSM model
bbp	particulate back-scattering coefficient at 443 nm (m-1)	GSM model
Kd(490)	diffuse attenuation coefficient at 490 nm (m-1)	analytical from merged CHL1
Lxxx	fully normalised water leaving radiances at xxx nm (mW/cm/m/sr) where xxx= 412, 443, 490, 510, 531, 550-565, 620, 665-670, 681(2) and 709(2) nm	weighted averaging method
L555	inter-calibrated fully normalised water leaving radiances at 555 nm (mW/cm/m/sr)	weighted averaging methods (1)
EL555	relative excess of radiance at 555 nm (%)	analytical from merged L555 & CHL1
T865	aerosol optical thickness over water (-)	weighted averaging methods
CF	cloud fraction (%)	classification & statistical methods

(1): spectral inter-calibration is applied prior to the merging.
(2): these MERIS water leaving radiances are not normalised.
: averaged data is only available from MERIS data.

The spatial and temporal resolution of the products distributed to the end-users are:

The GlobColour global level-3 binned products have a resolution of 1/24 at the equator (i.e. around 4.63 km) and consist of the accumulated data of all merged level 2 products, corresponding to periods of one day (a data-day algorithm is applied), 8 days and a calendar month. 8-days binning periods are continuous, starting from the first day of each calendar year.

The geographical location and extend of each bin is determined by the so-called Integerized Sinusoidal (ISIN) grid (see PUG for more details).

In GlobColour binned ISIN products, bins are always written in sequential order, from the southernmost-westernmost bin to the northernmost-easternmost bin. Only valid bins are written in a binned product. Land bins and bins with no contributions (i.e. uncovered bins) are not contained in the files as well as the covered bins where no valid data has been found. As a result, the actual number of bins cannot exceed an amount of approximately 71% of the total number of bins given above.

The spatial resolution of 1/24 yields to the following grid characteristics:

The GlobColour local products are defined at several specific areas called DDS areas.

There are several kinds of DDS products:

• DDS on PC grid, at a resolution of 1 km, computed from the level 2 tracks.
• DDS on ISIN grid, at a resolution of 1/24, computed from the level 2 tracks.
• DDS on ISIN grid, at a resolution of 1/24, at daily, 8-days and monthly time scale. They are computed the same way as the global merged level-3 products.

The local ISIN grid is defined to be fully compatible with the global ISIN grid. The numbering of the local DDS bins is computed from the global ISIN grid.

The local ISIN grid is defined to includes the corresponding local PC grid, i.e. the 100x100 km² area of the PC grid is fully covered with the local ISIN grid bins.

All DDS products are generated for a set of fixed DDS areas, and also for a set of DDS areas where in-situ measurements are available.
DDS on ISIN grid at daily, 8 days and monthly time scale can be either computed from the DDS on ISIN grid at track level (following the computation path of the global ISIN products) or from the global merged level 3 products.

The European Service for Ocean Colour - GlobColour is an ESA Data User Element Project