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CERES produces many official data products available publically
from the
Langely Atmospheric Data Center. "FSW" comes from the phrase:
"Flux and Clouds Regional SWath". To understand the
FSW data product one must have a sense of the two previous CERES
advanced data products, the Single Satellite Footprint (SSF) and
the Clouds & Radiative Swath (CRS) data products since FSW is the
first gridded version of the CRS data product. The following
paragraphs attempt to quickly outline these three CERES data products
and their relationship to one-another.
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| CERES Project |
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NASA's Clouds & the Earth's Radiant Energy System (CERES) project
flies scanning radiometers measuring broadband radiances (SW 0.2-4.0microns),
Total(0.2-200microns) and Window (8.0-12.0microns) (LW defined as Total - SW)
aboard the TRMM, EOS Terra and Aqua satellites. Radiance is converted to flux
using LW directional and SW anisotropic directionial models developed using
the CERES instruments unique scanning capabilities. These instruments are a
follow on to NASA's Earth Radiation Budget Experiment (ERBE) which flew in
the 1980's and 1990's. It's primary mission is to determine the Earth's
radiation budget at the Top of the Atmopshere (TOA). |
| Single Satellite Flux Data Product (SSF) |
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CERES pushes the science farther to create fusion data products which
incorporate the sophistication of the EOS satellites. In the SSF product,
high spatial resolution (1km) pixels from the MODerate resolution Imaging
Spectrometer (MODIS) instrument are collocated within the much larger
CERES footprint (~30km). The CERES Cloud Group analyzes these pixels
for statistical summaries of cloud and surface properties within the view of
the CERES instrument. Each SSF file contains one hour's worth of CERES.
footprints, typically around 1 million observations. |
| Clouds & Radiative Swath Data Product (CRS) |
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The second advanced CERES data product is the Clouds & Radiative Swath (CRS) .
In this part of CERES processing, the Surface and Atmospheric Radiatioin Budget
(SARB) group utilizes the CERES TOA observations, the accumlated cloud statistics
and surface information (from the SSF) and brings in ancillary atmospheric profile,
aerosol, ozone and surface characteristic information to run a fast radiation
transfer code for a subset of the CERES footprints. For every footprint we
execute radiation transfer model runs for pristine (no aerosol, no clouds),
clear, (with aerosol, no clouds) all sky (cloud and aerosol) and Clouds
No Aerosol (CNA) (with clouds, without aerosol). The model is run once for
each condition, then compared with the CERES TOA observation and, depending on the
scene viewed, various input parameters are modified to bring the model calculation
closer to the CERES observation. This is labeled the "tuned" run of the model. Flux
profile information at five model levels is combined with it's input SSF data and
together output as a CRS file. Again each CRS contains a swath of 1 hour's worth
of CERES footprints processed through the SARB algorithms. |
| CERES FSW Data Product |
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The FSW data product is an interim data product on the way to creating
global spatially averaged and temporally modeled CERES advanced data products.
The footprint data from the CRS (which recall includes everything in the SSF
product) are binned spatially on the CERES (aproximate equal area) 1 degree grid
and binned temporally within each local hour box for a month. There are, for 31 days,
744 hour "boxes" in a month. The footprints data collected in these spatial/temporal
box are averaged for each grid/hour . They are then collected and output for a month.
CERES outputs only the hour boxes with data in them but all grid boxes in 5 zonal
bands per file. Since the number of spatial grid boxes varies by latitude and CERES
temporal sampling increases with increasing latitude, the FSW does not have a fixed
file size. However they run approximately 50MB/file. To pull out a global map one
has to download 36 files and piece the hour boxes back together. These are,
obviously, fairly complex files. |
| FSW Surface Albedo Maps |
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Given the complex nature of FSW files the SARB attempts to create a simpler file
to use. These are not "official" CERES data products and conceivably can be reproduced
by anyone willing to download the FSW data and crunch the numbers.
We have extracted from the FSW files, the SARB radiation transfer model results
for tuned, clear sky shortwave upward and downward surface fluxes. (Note this is the
"clear sky" model run. The footprint may have clouds within it's view but recall we
run the model for clear and cloudy conditions.) We use these fluxes to calculate a
surface albedo then average availabe hour box data across the month for a "monthly
mean, clear sky" surface albedo. Monthly mean is in quotes because the values are not
full diurnal cycle monthly means but instead a mean of the albedos observed within a
1 degree region at the time of the EOS Terra satellite overpass of the region. Along
with the mean albedo the data files supply the mean cosine solar zenith angle at
which the observations were made, a parameter which can be used to move the albedo
in terms of solar zenith angle and a flag indicating snow or no snow in the grid box. |
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