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[CIDC FTP Data]
[ERBE Longwave Radiant Flux]
Data Access
Outgoing Longwave Radiant Flux from the Earth Radiation Budget
Experiment
[rule]
Readme Contents
Data Set Overview
Sponsor
Original Archive
Future Updates
The Data
Characteristics
Source
The Files
Format
Name and Directory Information
Companion Software
The Science
Theoretical Basis of Data
Processing Sequence and Algorithms
Scientific Potential of Data
Validation of Data
Contacts
Points of Contact
References
[rule]
Data Set Overview
This data set is a collection of monthly means of outgoing
longwave radiation derived from the Earth Radiation Budget
Experiment (ERBE) scanning instruments aboard the ERBS, NOAA-9,
and NOAA-10 satellites. It was created from the Regional, Zonal
and Global Gridded Averages (ERBE S-4G) data product, and cover
the years 1986 -1988. More years will be added as the data is
regrided.
The Earth Radiation Budget Experiment is a system of satellites
designed to measure the Earth's energy balance. Its goal is to
provide accurate measurements of incoming solar energy and
shortwave and longwave radiation reflected or emitted from the
Earth back into space. The Earth's radiation budget is the primary
indicator of global climate change. The absorbed shortwave
radiation (incident minus reflected) fuels the earth's climate and
biosphere systems. The longwave radiation represents the exhaust
heat emitted to space. It can be used to estimate the insulating
effect of the atmosphere (the greenhouse effect). It is also a
useful indicator of cloud amount and activity.
Sponsor
The production and distribution of this data set are being funded
by NASA's Earth Science enterprise. The data are not copyrighted,
however, we request that when you publish data or results using
these data please acknowledge as follows:
The authors wish to thank Dr. Bruce Barkstrom and the
ERBE Science Team at the NASA Langley Research Center
for originally producing this data, and the Distributed
Active Archive Center (Code 902) at the Goddard Space
Flight Center, Greenbelt, MD 20771, for putting the data
in the present format and distributing them. Goddard's
share in these activities was sponsored by NASA's Earth
Science enterprise.
Original Archive
The geophysical data from which the outgoing longwave radiation
data set is derived was originally produced by the ERBE Science
Team, led by Dr. Bruce Barkstrom (Barkstrom et al., 1989) in the
Atmospheric Sciences Division of NASA's Langley Research Center.
This data, designated as ERBE S4G, is currently available from the
Langley Distributed Active Archive Center at NASA Langley Reserach
Center. The original time- and space-averaged scanner data are on
a 2.5 degree by 2.5 degree grid. It has been regridded to 1 degree
by 1 degree for inclusion into this interdiscipline data
collection.
Future Updates
This data set will be updated as additional years and parameters
are regridded.
The Data
Characteristics
* Parameters: Outgoing longwave radiation, defined as the
amount of thermal infrared energy radiated per unit area per
unit time at the top of the atmosphere.
* Units: Watts per square meter (W/m2)
Typical Range (diurnal average): 100 -300 W/m 2
* Data Source: Earth Radiation Budget Experiment scanning
instruments aboard the ERBS, NOAA-9, and NOAA-10 satellites
* Temporal Coverage: January 1986 - December 1988
* Temporal Resolution: All values are monthly means
* Spatial Coverage: Global
* Spatial Resolution: 1 degree x 1 degree
SOURCE
Satellites
The ERBE instruments were carried aboard the ERBS, NOAA-9 and
NOAA-10 satellites. The scanner operation period and the nominal
orbit parameters for each satellite are:
ERBS:
* Launch date: October 5, 1984
* Orbit: non Sun-synchronous
* Nominal altitude: 610 km
* Inclination: 57 degrees
* Nodal period: 98 minutes
* Equatorial crossing time: Variable
* Scanner operated: November 1984 - February 1990
NOAA-9:
* Launch date: December 12, 1984
* Orbit: Sun-synchronous
* Nominal altitude: 872 km
* Inclination: 98 degrees
* Nodal period: 102.08 minutes
* Equatorial crossing time: 1420 local time (ascending), but
precessed to 1500 local time by December, 1986
* Scanner operated: February 1985 - January 1987
NOAA-10:
* Launch date: September 17, 1986
* Orbit: Sun-synchronous
* Nominal altitude: 833 km
* Inclination: 98 degrees
* Nodal period: 101.2 minutes
* Equatorial crossing time: 0731 local time (descending)
* Scanner operated: November 1986 - May 1989
Additional information on the NOAA satellites is available in the
NOAA Polar Orbiter Data User's Guide.
The objectives of the Earth Radiation Budget Experiment (ERBE)
were to:
* determine for a minimum of 1 year the monthly average
radiation budget on regional, zonal, and global scales
* determine the equator-to-pole energy transport gradient
* determine the average diurnal variation of the radiation
budget on a regional and monthly scale
Instrument
Broad spectral band measurements covering the range 0.2 to 50
micrometers are made by several sensors. Both the solar irradiance
at the satellite altitude and the earth-emitted longwave and
reflected shortwave radiances and irradiances are monitored. Both
scanning and non-scanning instruments are used.
Earth Radiation Budget Satellite (ERBS), NOAA-9, and NOAA-10 ERBE
Instrument Characteristics
Channel Spectral Range Measurement
(micrometers)
Fixed Total
WFOV* 1 0.2 - 50.0 Radiance
2 0.2 - 5.0 Shortwave
Reflected
Fixed Total
MFOV** 3 0.2 - 50.0 Radiance
4 0.2 - 5.0 SW
Reflected
Fixed
Solar 5 0.2 - 50.0 Total
Monitor Irradiance
Scanning Calibrated
NFOV~ 1 0.2 - 50.0 Radiance
2 0.2 - 5.0 SW
Reflected
3 5.0 - 50.0 Longwave
Emitted
* Wide Field-of-View
** Medium Field-of-View
~ Narrow Field-of-View
Details of the fixed WFOV, MFOV and Solar Monitor channels that
comprise the non-scanning instrument package will not be discussed
here but further information can be found in Barkstrom and Smith
(1986). The following presents a brief overview of the the
characteristics of the NFOV scanning instruments aboard the
various spacecraft.
The scanner package contains three radiometric detectors each of
which consists of an f/1.84 Cassegrain telescope. All are located
within a single, rotating scan-head which, when operating in the
cross track azimuth position, scans the Earth perpendicular to the
satellite ground track from horizon to horizon. The scan-head can
also be rotated in azimuth at a slow rate (0.9 degrees/second
NOAA, 0.675 degrees/second ERBS). Each detector samples 74
measurements per scan. The total detector has no filter and so
absorbs all wavelengths. The shortwave detector has a Suprasil-W1
filter which transmits only shortwave radiation. The longwave
detector has a multilayer filter on a diamond substrate to reject
shortwave and accept longwave radiation. To enhance the spectral
flatness of the detectors, each thermistor chip is coated with a
thin layer of black paint.
Instrument Measurement Geometry:
The scanner can rotate in azimuth between 0 degrees and 180
degrees with an accuracy of 0.075 degrees. The normal scan mode is
cross-track. The effective field of view of the scanner is 3
degrees. The NFOV channels on ERBS have an instantaneous hexagonal
FOV of about 3 x 4.5 degrees, which is equivalent to a 31 km
cross-track x 47 km along-track footprint at nadir. The NFOV
channels on NOAA have a 44 km cross-track x 65 km along-track
footprint. Spatial coverage is global for the scanners aboard the
NOAA polar orbiters, but restricted to latitudes between 57
degrees North and 57 degrees South for the ERBS scanner.
The NOAA ERBE scanner instruments generally provide 2 measurements
per day (day and night) over most of the globe, with more
measurements per site as the polar regions are approached due to
overlap of successive orbits. The ERBS ERBE scanner instrument,
due to its non sun-synchronous orbit and consequent orbital
precession, will sample all points between +/- 57 degrees latitude
at all local times sometime every 2 months.
A detailed description of the ERBS instruments and the ERBE,
NOAA-9 and NOAA-10 satellites are available on the Langley
Research Center's Distributed Active Archive Center's worldwide
web site.
The Files
This data set currently consists of 36 monthly mean data files for
the period January 1986 through December 1989 and a collection of
36 gif images derived from them.
Format
* File Size: 259200 bytes
* Data Format: IEEE floating point notation
* Headers, trailers and delimiters: none
* Land/water mask: none
* Fill value: -999.9
* Image orientation: North to South
Start position: (179.5W, 89.5N)
End position: (179.5E, 89.5S)
Name and Directory Information Naming Conventions
The file naming convention listed below was derived for the Unix
operating system, and may be too long for PC systems. This will
result in the file names being truncated to eight characters with
a three character extension.
The file naming conventions for the ERBE OLR data set on a Unix
system are:
erbe.lwolr.1nmegg.[yymm].ddd
where:
erbe = data product designator (ERBE)
lwolr = parameter name (outgoing longwave radiation)
1 = number of levels
n = vertical coordinate, n = not applicable
m = temporal period, m = monthly
e = horizontal grid resolution, e = 1 x 1 degree
gg = spatial coverage, gg = global (land and ocean)
yy = year
mm = month
ddd = file type designation (bin=binary, ctl=GrADS control
file)
Directory Path to Data Files
* data/inter_disc/radiation_clouds/erbe_rad/yyyy/
where yyyy is the year
Companion Software Several software packages have been made
available on the CIDC CD-ROM set. The Grid Analysis and Display
System (GrADS) is an interactive desktop tool that is currently in
use worldwide for the analysis and display of earth science data.
GrADS meta-data files (.ctl) have been supplied for each of the
data sets. A GrADS gui interface has been created for use with the
CIDC data. See the GrADS document for information on how to use
the gui interface.
Decompression software for PC and Macintosh platforms have been
supplied for datasets which are compressed on the CIDC CD-ROM set.
For additional information on the decompression software see the
aareadme file in the directory:
software/decompression/
Sample programs in FORTRAN, C and IDL languages have also been
made available to read these data. You may also acquire this
software by accessing the software/read_cidc_sftwr directory on
each of the CIDC CD-ROMs
The Science
Theoretical Basis of Data
The Earth's radiation budget consists of three components:
incoming solar, reflected solar, and Earth-emitted radiation. The
incoming radiation from the sun is either reflected by the Earth's
atmosphere and surface, or is absorbed. Over the course of a year
the globally absorbed shortwave radiant energy is essentially
balanced by the thermal logwave radiation emitted to space. The
energy that is absorbed by the surface and atmosphere drives our
weather and climate. On average, more energy is absorbed near the
equator than near the poles. This results in a transfer of energy
from equatorial to polar zones, where more radiation is emitted
than absorbed. This serves to further magnify the dynamics of the
climate.
An accurate study of the radiation budget can only be done from
above the atmosphere because the atmosphere itself is one of the
elements of the radiation budget. To study the diurnal cycles of
the radiation budget at any geographic location, more than one
satellite is needed to obtain the necessary sampling rate
(Barkstrom and Smith, 1986). Since a single satellite in
sun-synchronous, polar orbit cannot provide independent
information on synoptic and seasonal effects, an additional
satellite in a highly inclined orbit (e.g., 57 degrees) is
required in order to periodically sample all locations at all
local times between the latitudes defined by the inclination
(e.g., between 57N and 57S). Poleward of 57 degrees latitude, a
second sun-synchronous satellite with an equatorial crossing time
6 to 7 hours out of phase with the first polar orbiter will
provide the additional sampling necessary for determination of
diurnal effects at these higher latitudes. Examples of the
variability of the diurnal cycle of outgoing longwave radiation
with latitude and surface type can be found in Harrison et al.
(1988).
Processing Sequence and Algorithms
The individual scanner measurements were collected, Earth located,
and calibrated to produce radiance measurements at the satellite.
The measurements from the ERBS, NOAA-9, and NOAA-10 spacecraft
were handled separately. The simultaneous short and longwave
scanner observations for a given scene were used to identify the
scene as one of twelve model types: clear land, desert, ocean,
coast (mixed land & ocean) or snow; partly or mostly cloudy over
land/desert, ocean, or coast; the twelfth scene was overcast
(Wielicke and Green, 1989). First a scene dependent adjustment was
made to account for the non-flat spectral response of the sensor.
Scene dependent angular models were then used to infer the
longwave irradiance from each individual longwave radiance
measurement. This last step was termed inversion. The scanner
measures a ray coming out from a given region towards the
satellite in units of watts per meter squared per steradian.
Inversion estimates the total integral over all outward angles to
yield the irradiance at the satellite altitude in watts per meter
squared over a specific geographic region.
In the scanner time and space averaging a 2.5 degree by 2.5 degree
world grid was used (72 latitude bands by 144 meridian columns).
In practice all polar cap measurements were entered in the first
polar grid box. Thus there were 70 latitude bands plus two polar
caps. For each grid box a monthly hour x day matrix was then set
up for each month (24 x N, were N= number of days in the month).
The scene tagged measurements were then sorted into this hour x
day matrix. Most of the hour x day boxes for the month had no
observations. For the longwave case all the hour x day boxes for
the month without observations were filled by interpolation. Over
land/desert on a given day, if there was at least one daylight
longwave observation at least one hour after sunrise and one hour
before sunset plus at least one before sunrise and one after
sunset, then a half sine curve centered at noon was used as the
interpolation function. This was done because there is usually a
large diurnal longwave variation over land/desert. This was only
done if the daylight observation was larger than the two night
time observations. In all other longwave cases a linear
interpolation was used.
The monthly means were determined in two ways: the columns were
averaged to obtain daily means and then these were averaged to get
the monthly daily mean; alternately the rows were averaged to get
monthly hourly means and these were averaged to obtain monthly
hourly means. For the scanner products the two monthly means
almost always agreed very closely. Note that both the longwave and
shortwave products represent the means over the 24 hours in the
day. More details can be found in the ERBE S4 (monthly means)
User's Guide.
The 2.5 x 2.5 degree monthly mean data set containing ERBE
outgoing longwave radiant flux was used by the Sounder Research
Team at NASA/GSFC for comparison with independent estimates of
this field included as part of the TOVS Path A Pathfinder suite of
geophysical parameters. Since the TOVS Pathfinder level 3 products
are mapped to a 1 degree by 1 degree grid, the ERBE data were
regridded by the Sounder Research Team to facilitate comparisons.
These were then delivered to the Goddard DAAC to be included as
part of the interdisciplinary data collection. The following steps
were performed by Sounder Research Team in the regridding process:
1. Starting with the first latitude band in the original data
set (87.5N to 90N), the first pair of grid cells (total of 5
degrees in longitude) was partitioned into five cells each of
width 1 degree; cells 1 and 2 were assigned the value of the
first 2.5 degree cell, cells 4 and 5 the value of the second
2.5 degree cell, and cell 3 the arithmetic average of the
values of the first and second 2.5 degree cells.
2. In Step 1, if either (but not both) of the original 2.5
degree cells is a fill value, then no average is performed
and cell 3 is assigned the value of the unfilled 2.5 degree
cell. If both of the original cells are fill values, then
cell 3 is likewise assigned this fill value.
3. Steps 1 and 2 were repeated for the remaining 71 pairs of 2.5
grid cells in the original data set
4. Steps 1 through 3 were performed for the remaining 71
latitude bands in the original data set to arrive at a
temporary array of size 360 x 72 (1 degree longitude by 2.5
degrees latitude)
5. The entire procedure above was repeated in the latitudinal
direction using the same grid cell partitioning scheme to
arrive at the final 360 x 180 (1 degree longitude by 1 degree
latitude) array.
6. The regridded data were visually examined to ensure
consistency with the original data.
Scientific Potential of Data
Measurements of the radiation budget provide one of the important
tools for the validation of numerical models of the atmosphere.
They also provide possibilities for "climate experiments" by
allowing the sensitivity of the radiation budget to various
forcings to be studied empirically.
The use of cloud discrimination from ERBE has provided a
significant source of information on the influence of clouds and
the characteristics of clear-sky energy fluxes. This information
is particularly important in understanding cloud forcing in the
atmosphere. It is also important for investigating the response of
clouds, or cloud sensitivity to climate change. Some examples of
studies which benefit from global measurements of outgoing
longwave radiation include:
* Radiation budget studies (absorption and emission of solar
and longwave radiation by ocean, land and atmospheric gases.)
(Kyle et al., 1986)
* Distribution and density of cloudiness and their effect upon
global climate and regional weather patterns (Harrison et
al., 1990; Arking, 1991)
* Validating and tuning general circulation models (GCMs),
which have many geophysical parameters based on the initial
conditions of radiative balance (Cess et al., 1990)
* Determining the equator to pole energy transfer and resultant
impact on regional weather and climate (Sohn and Smith, 1993)
Validation of Data
Monthly "hour x day" matrices and resultant monthly means were
calculated both for each satellite separately and for the combined
measurements from all the operating ERBE instruments. The ERBE
Science Team carefully cross checked the calibration of the three
ERBE instruments. In the combined scanner products there are
slight bias shifts in the global means in November 1986 when the
NOAA-10 measurements start to be included and a somewhat larger
shift in February 1987 indicating the end of the NOAA-9
measurements. These bias shifts are largest in the emitted
longwave and net radiation ( see for instance Kyle et al. 1993).
These bias shifts arise chiefly from the difference in the local
measurement times of the NOAA-9 and the NOAA-10 satellites.
Regionally and seasonally these differences can be fairly large
(Hartmann et al., 1991).
Data Access and Contacts
FTP Site
Points of Contact
For information about or assistance in using any DAAC data,
contact
EOS Distributed Active Archive Center(DAAC)
Code 902
NASA Goddard Space Flight Center
Greenbelt, Maryland 20771
Internet: daacuso@daac.gsfc.nasa.gov
301-614-5224 (voice)
301-614-5268 (fax)
References
Arking, A., 1991, The radiative effects of clouds and their impact
on climate, Bull. Amer. Meteor. Soc., 72, 795-813.
Barkstrom, B. R., and G.L. Smith, 1986, The Earth Radiation Budget
Experiment: science and implementation, Rev. Geophys., 24,
379-390.
Barkstrom, B.R., E. Harrison, G. Smith, R. Green, J. Kibler, R.
Cess, and the ERBE Science Team, 1989, Earth Radiation Budget
Experiment (ERBE) archival and April 1985 results, Bull. Amer.
Meteor. Soc., 70, 1254-1262.
Cess, R.D., et al., 1990, Intercomparison and interpretation of
climate feedback processes in 19 atmospheric general circulation
models, J. Geophys. Res., 96, 16601-16615.
Harrison, E.F., D.R. Brooks, P. Minnis, B.A. Wielicki, W.F.
Staylor, G.G. Gibson, D.F. Young, F.M. Denn, and the ERBE Science
Team, 1988, First estimates of the diurnal variation of longwave
radiation from the multiple-satellite Earth Radiation Budget
Experiment (ERBE), Bull. Am. Meteorol. Soc., 69, 1144-1151
Harrison, E.F., P. Minnis, B.R. Barkstrom, V. Ramanathan, R.D.
Cess, and G.G. Gibson, 1990, Seasonal variation of cloud radiative
forcing derived from the earth radiation budget experiment, J.
Geophys. Res., 95, 18687-18703.
Hartmann, D. L., K. J. Kowalewsky, and M. L. Michelsen, 1991,
Diurnal variations of outgoing longwave radiation and albedo from
ERBE scanner data, J. Climate, 4, 598-617.
Kyle, H.L., K.L. Vasanth, and the Nimbus-7 ERB Experiment Team,
1986, Some characteristic differences in the earth's radiation
budget over land and ocean derived from the Nimbus-7 ERB
Experiment, J. Climate Appl. Meteor., 25, 958-981.
Kyle, H. L., J. R. Hickey, P. E. Ardanuy, H. Jacobowitz, A.
Arking, G. G. Campbell, F. B. House, R. Maschhoff, G. L. Smith, L.
L. Stowe, and T. Vonder Haar, 1993: The Nimbus Earth Radiation
Budget (ERB) Experiment: 1975 to 1992, Bull. Amer. Meteor. Soc.,
74, 815-830.
Sohn, B.J., and E.A. Smith, 1993, Energy transports by ocean and
atmosphere based on an entropy extremum pronciple. Part I: Zonal
averaged transports, J. Climate, 6, 886-899.
Wielicki, B.A., and R.N. Green, 1989: Cloud identification for
ERBE radiative flux retrieval, J. Appl. Meteor., 28, 1131-1146.
------------------------------------------------------------------------
[NASA] [GSFC] [Goddard DAAC] [cidc site]
NASA Goddard GDAAC CIDC
Last update:Tue Aug 19 16:43:21 EDT 1997
Page Author: Lee Kyle -- lkyle@daac.gsfc.nasa.gov
Web Curator: Daniel Ziskin -- ziskin@daac.gsfc.nasa.gov
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