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International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences, Vol XXXV, Part B4. Istanbul 2004
The objective is to generate a global DSR product from the
fusion of geo-stationary meteorological satellites and polar
sensor systems. The global cover at mid latitudes will be
ensured by all available geo-stationary satellites: METEOSAT-
7 for Europe and Africa, METEOSAT-5 for the Indian Ocean,
GMS-5 for Japan and Australia, GOES-10 over the Pacific
Ocean, GOES-8 over Americas. The zonal gap between
METEOSAT-5 and GMS-5 should be filled in by both the
Indian INSAT satellite series and the Chinese FY-2 satellite
series. The sun-synchronous satellite NOAA/AVHRR covers
the adjacent polar regions. The high frequency of measurements .
by the geo-stationary instruments allows to yield a product on
the hourly basis.
850
bSSF in W/m*
200
0
MSC - 1 /SEVIRI
Figure 9. Simulated DSR flux over the MSG disk area.
45 Downwelling Longwave Radiation Flux
The Down-welling Long-wave Radiation (DLR) flux (W.m-2)
is defined as the thermal irradiance reaching the surface in the
thermal infrared spectrum (4-100 pm). It is determined by the
radiation that originates from a shallow layer close to the
surface, about one third being emitted by the lowest 10 meters
and 80% by the 500-meter layer.
It is a particularly difficult parameter to retrieve since it cannot
be directly measured by satellites. However, Radiative Transfer
Models (RTM) may be used to estimate DLR from atmospheric
profiles (temperature and humidity), if the cloudiness is known.
MU IS
+A
©
MSG
787
Figure 10. Land SAF DLR flux output product for MSG full
disk 12.02.2003 - 12 UTC
The strategy consists in using conjointly satellite images from
METEOSAT and NOAA to derive cloudiness, and two-meter
air and dew point temperatures and precipitable water contents
from ECMWF weather forecast data in RTM bulk empirical
parameterizations.
4.6 Land Surface Temperature
The land surface temperature (LST) is defined as equivalent to
the surface emitted radiance in the field-of-view of the sensor,
according to Planck's law. The surface emitted infrared
radiance is determined by "atmospheric correction" of the top
of atmosphere radiance measured by the satellite in the 12 um
window range. The atmospheric correction takes the reflected
part of the down-welling radiance and the attenuation of the up-
welling radiance in the atmosphere into account.
ji BE TEE a4
Time of maximum temperature
(hour)
.s WEE Em BE TREE 45
Temperature end of night Diurnal Temperature Amplitude
(°C) (°C)
Figure 11. Land Surface Temperature indicators representatives
for August 1996, derived from METEOSAT.
LST is retrieved from METEOSAT thermal infrared channel
images using a neural network. METEOSAT is the only
satellite that provides infrared measurements over Africa and
Europe that resolves the diurnal wave of LST (Figure 11). The
disadvantage of METEOSAT is that only one infrared channel
is available. Thus established LST (and Sea Surface
Temperature) determination methods like split-window
technique can not be used and the atmospheric state can not be
derived from METEOSAT data. The atmospheric situation (i.c.
the temperature and moisture profiles) are taken from ECMWF.
The physics of the atmospheric correction of a single infrared
channel is the following: Calculate the expected satellite
measurement for a reasonable range of land surface
temperature, surface elevation and emissivity for the actual
profiles and viewing angle — this constitutes the forward
calculation of atmospheric radiances. The LST is then
determined by interpolation to the actual satellite measurement
(this is the inversion of the forward calculation) for profiles
around the current pixel and horizontal interpolation of the
atmospheric correction at the surrounding pixels.
4.7 Soil Moisture
A database of soil moisture products is derived from active
microwave measurements (ERS-1/2 scatterometer). One
parameter of the database is the topsoil moisture content
(surface wetness). The topsoil moisture is a relative measure of
soil moisture in the first 5 cm of the soil ranging between 0 and
100 representing the degree of saturation. The other parameter
is the Soil Water Index (SWI). The SWI is a relative measure of
