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Presentation of the Products
Atlantic Sea Surface Temperature
For further details consult the
Atlantic Sea Surface Temperature Product Manual
Physical definition
Subskin SST : Comparable to in situ (buoy) measurements at night.
Relation to bulk SST : equivalent to bulk SST by night. By day, a bias of
several Kelvin may be found under favorable diurnal heating conditions.
Relation to skin SST : by day and by night the subskin SST
is convertible to skin temperature by subtracting 0. 2K.
Delivered products
The delivered SST products are :
The LML SST, 3-hourly means centered
on 0100, 0400, 0700,...h UTC , derived from the geostationary satellite
data (GOES and MSG), covering the oceanic area from 60 N to 60 S and from
100 W to 45 E , at 0.1 degree resolution,
The MAP SST, 12-hourly means
centered on 0000 and 1200 h UTC, derived from GOES, MSG and NOAA polar
orbiter satellite data, covering the oceanic area from 90 N to 60 S and
from 100 W to 45 E , at 0.1 degree resolution.
SST products are accessible to all users on
Météo-France and IFREMER ftp servers, via EUMETCAST,
and may be delivered on request through the Regional Meteorological
Data Communication Network (RMDCN) to the European Meteorological
services in GRIB format.
Satellites data sources
The LML SST products are derived from Met-08 and GOES-12.
The MAP SST are derived from Met-08, GOES-12 and NOAA polar satellites.
Product content
Main product : subskin SST
Associated field 1 : time : the mean time of the product calculated for every pixel
Associated field 2 : quality indexes : they include information on the processing conditions and confidence levels defined for each pixel:
5 excellent, 4 good, 3 acceptable, 2 bad, 1 erroneous, 0 unprocessed.
Unit and range
CentiKelvins. When using GRIB format, a scaling factor of 100 must be applied.
No lower limit is imposed on the SST calculations, providing the sea is ice free/
The expected range is thus about -3°C till 35°C, corresponding to the actual values
of 27000 to 30800. Unprocessed data (for whatever reason) show a negative value (-32768)
in HDF format, or is flagged as missing in GRIB section 3.
Processing scheme
At Met.no :
For each satellite pass (NOAA and further METOP) received at Met.no,
data are processed to produce HL SST fields according the following scheme :
HL SST calculation scheme
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At CMS :
GOES or MSG IR data are processed every hour, producing instantaneous
Sea Surface Temperature solar irradiance fields. The hourly processing
scheme is described below.
LML SST calculation scheme
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The hourly SST fields are combined to produce 3-hourly and 12-hourly SST fields,
separately for each satellite, GOES or MSG.
The GOES and MSG 3-hourly or 12-hourly SST fields are merged into a LML
product.
Finally, the 12-hourly LML and 12-hourly HL, derived from NOAA
and produced by Met.no and DMI, are merged into the MAP product.
In overlapping areas, several values may be available. A merging process selects the
best, so that any final SST value is derived from one unique satellite.
Algorithm
The algorithms used are in principle the following :
-
split window Nls algorithms (applied by day and night on the AVHRR data
and by day ont the geostationary satellites having the split window capacity) :
Ts=A0 T11 + (B1 S + B2 Tsclim) (T11-T12) + C0
-
triple window T3.7 algorithms (by night only on the geostationary satellites
having the split window capacity) :
Ts=(D0 + D1S) T3.7+ (E0 + E1S) (T11-T12) + F0 + F1S
-
dual window algorithms (by night only on the geostationary satellites
without the split window capacity, e.g. GOES-12) :
Ts=(G0 + G1S) T11 + (H0 +
H1S) (T3.7-T11) + I0 + I1S
(Ts: calculated SST, T3.7, T11 and T12 : brightness
temperatures in channels 3.7, 11 and 12 micron, S= sec(teta)-1 with teta:
satellite zenith angle, Tsclim: climatologic SST values; all temperatures
are in Celsius).
Current parameters:
The algorithm coefficients and the values of the thresholds used in the processing are described in a configuration file:
