GERB Data Formats
This page aims to give you a brief description of the various
formats used to disseminate and archive the GERB data.
A complete description is available in the Chapter 2 of the
GERB level 2 User Guide
.
Introduction
The GERB level 2 data provide TOA unfiltered radiance and flux for
the SW and LW.
The level 2 data are available in 3 formats that differ
in the spatial and temporal processing applied to the
GERB observations.
Although the geolocation of the GERB footprint (PSF) is changing at
each scan, the level 2 data are always provided on constant
rectified geostationary grids.
Therefore, the production of the GERB level 2 data involves
rectification processes which are different for the
3 formats as described in Dewitte et al.,(2008)
(see Publications in the main menu) and summarized
hereafter.
ARG : Averaged Rectified Geolocated
The Averaged Rectified and Geolocated (ARG) data are an
average of three successive GERB scans (covering a period of
approximately 17 minutes) presented on
a regular (in viewing angle) grid with a sampling distance
of 44 km x 44 km at nadir.
The ARG values are obtained by bilinear interpolation of the
original observations.
As no attempt is made to correct for the GERB PSF the radiance
and flux values at each grid point are representative of the
energy from a larger region than the grid spacing.
Additionally, the GERB geolocation noise and the linear
interpolation of the observations will affect the radiance
and flux values at each point.
BARG : Binned Averaged Rectified Geolocated
The Binned Averaged Rectified and Geolocated (BARG)
products are averages over fixed 15 minute time intervals
(00:00 to 00:15 UTC, 00:15 to 00:30 UTC, etc) presented on
a regular (in viewing angle) grid with a spacing of
45 km x 45 km at nadir.
The processing is considerably more complex than for
the production of the ARG data.
It attempts to remove the effect of the PSF, and also
provides corrections for errors that may have been
introduced in the ARG by the geolocation and
rectification processes.
This is achieved by using fine scale
estimates of the broadband SW and LW radiances
inferred from NB measurements made by the SEVIRI instrument
on the same MSG satellite.
Merging the GERB BB observations and the fine--scale SEVIRI BB estimates
results in level 2 BARG radiances and fluxes which are representative
of the radiation from exact 15 x 15 SEVIRI pixel areas
(i.e. 45 km x 45 km).
HR : High Resolution
Finally, the High Resolution (HR) product is presented on a
grid with a spacing of 3 x 3 SEVIRI pixels
(i.e. 9 km x 9 km at nadir).
It is provided every 15 minutes as instantaneous
values at the time of the SEVIRI observations.
As for the BARG, fine scale estimates of the BB radiances from SEVIRI
are combined with GERB observations to produce the GERB High Resolution
data.
The GERB HR product is requested to study the radiation budget
at relatively small scales (e.g. valley fog).
Data at Stations
For this product, the main quantities are extracted during the processing
for a list of pre-defined pixels.
These pixels correspond to existing radiometric ground stations.
Each 15' and for each station, the data are appended in an ASCII file.
This product is designed for processing validation and comparison with
ground measurement over extended temporal periods.
More info here.
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