CIDC FTP Data
ERBE Longwave Radiant Flux

Data Access

Outgoing Longwave Radiant Flux from the Earth Radiation Budget Experiment
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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

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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

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:

NOAA-9:

NOAA-10:

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:

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

ChannelSpectral Range (micrometers)Measurement
Fixed WFOV*
1
0.2 - 50.0
Total Radiance

2
0.2 - 5.0
Shortwave Reflected
Fixed MFOV**
3
0.2 - 50.0
Total Radiance

4
0.2 - 5.0
SW Reflected
Fixed Solar Monitor
5
0.2 - 50.0
Total Irradiance
Scanning NFOV~
1
0.2 - 50.0
Calibrated Radiance

20.2 - 5.0SW Reflected

35.0 - 50.0Longwave 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

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

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:

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).

Contacts

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
NASAGoddardGDAACCIDC

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
NASA official: Paul Chan, DAAC Manager -- chan@daac.gsfc.nasa.gov