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Earth Syst. Sei. Data, 8, 235-252, 2016
ical Data Center ETOPOl; Amante and Eakins, 2009). For
observations where the closest water depth was above sea
level (e.g. data collected very near the coast), it was given
the value of zero.
Data processing thus included two major steps: prepro
cessing and merging. The first step was related to each set
of contributing datasets in particular and aimed to identify
problems and convert the data of interest to a standard for
mat. The second step dealt with the integration of all data
into one unique hie and included the elimination of dupli
cated data between the individual sets of data acquired. In
the next subsections a brief overview of each original set of
data is provided.
2.2 Preprocessing of each set of data
2.2.1 Marine Optical Buoy (MOBY)
The Marine Optical Buoy (MOBY) is a fixed mooring sys
tem operated by the National Oceanic and Atmospheric Ad
ministration (NOAA) that provides a continuous time series
of water-leaving radiance and surface irradiance in the visi
ble region of the spectra from 1997 onwards. The site is lo
cated a few kilometres west of the Hawaiian island of Lana’i
where the water depth is about 1200 m. Since its deployment,
MOBY measurements have been the primary basis for the
on-orbit vicarious calibrations of the SeaWiFS and MODIS
ocean-colour sensors. A full description of the MOBY sys
tem and processing is provided in Clark et al. (2003). Data
are freely available for scientific use at the MOBY Gold di
rectory. The products of interest are the Scientific Time Se
ries hies, which refer to MOBY data averaged over sensor-
specific wavelengths and particular hours of the day (around
20:00-23:00 UTC). For this work, the satellite band-average
products for SeaWiFS, MODIS AQUA and MERIS were
compiled from the January 2005 reprocessing for the early
data and from the latest reprocessing for data after 2011.
The “inband” average subproduct was used, and to main
tain the highest quality, only data determined from the upper
two arms (Fwl) and hagged “good” quality were acquired.
Data from the MOBY203 deployment were discarded due
to the absence of surface irradiance data. The compiled vari
able was the remote-sensing rehectance, rrs, which was com
puted from the original water-leaving radiance (Fw) and sur
face irradiance (Es). The water-leaving radiances were cor
rected for the bidirectional nature of the light held (Morel
and Gentili, 1996; Morel et al., 2002) using the same look-up
table and method as that used in the SeaWiFS Data Analy
sis System (SeaDAS) processing code. As mentioned before,
the MOBY data compiled in this work are sensor-specific.
Therefore, attention is necessary to use the correct MOBY
data when validating a particular sensor. The way MOBY
data are stored in the final merged table is consistent with
the original wavelengths; however, these wavelengths can
differ from what is sometimes expected to be the central
wavelength of a given band and sensor. Irrespective of the
wavelength where MOBY data are stored in the final ta
ble, for validation of bands 1-6 of SeaWiFS, MOBY data
stored in the final merged table at 412, 443, 490, 510, 555
and 670 nm, respectively, should be used. For validation of
bands 1-6 of MODIS AQUA, MOBY data stored in the final
merged table at 416, 442, 489, 530, 547 and 665 nm, respec
tively, should be used. Finally, for validation of bands 1-7
of MERIS, MOBY data stored in the final merged table at
410.5, 440.4, 487.8, 507.7, 557.6, 617.5 and 662.4 nm, re
spectively, are the appropriate data.
2.2.2 BOUée pour I’acquiSition de Séries Optiques à
Long termE (BOUSSOLE)
The BOUée pour F acquisition de Séries Optiques à Fong
termE (BOUSSOFE) project started in 2001 with the ob
jective of establishing a time series of bio-optical properties
in oceanic waters to support the calibration and validation
of ocean-colour satellite sensors (Antoine et al., 2006). The
project is composed of a monthly cruise program and a per
manent optics mooring (Antoine et al., 2008). The mooring
collects radiometry and inherent optical properties (IOPs)
in continuous mode every 15 min at two depths (4 and 9 m
nominally). The monthly cruises are devoted to the mooring
servicing, to the collection of vertical profiles of radiome
try and IOPs, and to water sampling at 11 depths from the
surface down to 200 m, for subsequent analyses including
phytoplankton pigments, particulate absorption, CDOM ab
sorption and suspended particulate matter load. The BOUS
SOFE mooring is in the western Mediterranean Sea at a wa
ter depth of 2400 m. All pigment (2001-2012) and radio-
metric (2003-2012) data were provided by the principal in
vestigator. The compiled variables were rrs and chla_hplc.
Observations of the diffuse attenuation coefficient (kd) were
not included in the present compilation, as they were un
der internal quality revision at the time of data acquisition.
Remote-sensing reflectance was computed from the original
“fully normalised” water-leaving radiance (nFw_ex), which
is the “normalised” water-leaving radiance (nFw previously
described), with a correction for the bidirectional nature of
the light held (Morel and Gentili, 1996; Morel et al., 2002).
The solar irradiance (Fo) was computed from two available
variables in the original set of data - nFw and rrs - using the
equation Fo = nFw/rrs. Only radiometric observations that
meet the following criteria were used: (1) tilt of the buoy was
less than 10°; (2) the buoy was not lowered by more than
2 m as compared to its nominal water line (to ensure the Es
reference sensor is above water and exempt from sea spray);
and (3) the solar irradiance was within 10 % of its theoretical
clear-sky value (determined from Gregg and Carder, 1990).
The latter criterion was used to select clear skies only. An
additional quality control was to remove observations that
were 50 % higher or lower than the daily average. This re
moved a small number of spikes in the time series. The final
