1.  TITLE

1.1  Data Set Identification.

     ERBE S4 Clear-Sky Albedo.

     (Monthly Mean Albedo ; NASA/LaRC)

1.2  Data Base Table Name.

     Not applicable.

1.3  CD-ROM File Name. 


     Note:  capital letters indicate fixed values that appear on the CD-ROM 
     exactly as shown here, lower case indicates characters (values) that 
     change for each path and file.

     The format used for the filenames is: ERYyyMmm.sfx, where yy is the last 
     two digits of the year (e.g., Y87=1987), and mm is the month of the year 
     (e.g., M12=December).  The filename extension (.sfx), identifies the data 
     set content for the file (see Section 8.2) and is equal to .ALB for this 
     data set.

1.4  Revision Date Of This Document.

     April 5, 1995.

2.1  Investigator(s) Name and Title.

     Dr. Bruce R. Barkstrom
     Radiation Sciences Branch
     NASA Langley Research Center

2.2  Title of Investigation.

     Earth Radiation Budget Experiment.

2.3  Contacts (For Data Production Information).

              |         Contact 1        |        Contact 2          |
2.3.1 Name    |Mr. Edwin F. Harrison     |Dr. Bruce R. Barkstrom     |
2.3.2 Address |Mail Stop 420             |Mail Stop 420              |
              |Radiation Sciences Branch |Radiation Sciences Branch  |
              |NASA/LaRC                 |NASA/LaRC                  |
      City/St.|Hampton, VA               |Hampton, VA                |
      Zip Code|23681-0001                |23681-0001                 |
2.3.3 Tel.    |(804) 864-5663            |(804) 864-5656             |
2.3.4 Email   |||

              |        Contact 3       |
2.3.1 Name    |Mr. David F. Young      |
2.3.2 Address |Lockheed Engineering    |
              |& Sciences Co.          |
              |144 Research Drive      |
      City/St.|Hampton, VA             |
      Zip Code|23666                   |
2.3.3 Tel.    |(804) 766-9674          |
2.3.4 Email   | |

2.4 Requested Form of Acknowledgment.

    Please cite the following publication when these data are used:

      Barkstrom, B. R., E. F. Harrison, and R. B. Lee, 1990.  Earth Radiation 
          Budget Experiment, Preliminary seasonal results.  EOS Transactions, 
          American Geophysical Union, 71, February 27.

                            3.  INTRODUCTION

3.1 Objective/Purpose.

    The goals of the Earth Radiation Budget Experiment (ERBE) are (1) to 
    understand the radiation balance between the Sun, Earth, atmosphere, and 
    space and (2) to establish an accurate, long-term  baseline data set for 
    detection of climate changes.  Earth radiation budget (ERB) data are 
    fundamental to the development of realistic climate models and to the 
    understanding of natural and anthropogenic perturbations of the climate 
    system.  As part of ERBE, measurements of broadband shortwave radiation 
    reflected from the Earth-atmosphere system were obtained, from which 
    albedo values were calculated.  In addition, values from scenes determined 
    to be free of clouds were analyzed separately and clear-sky albedos were 

3.2 Summary of Parameters.

    For this study, only the clear-sky albedos are included.

3.3 Discussion.

    Clear-sky albedos were obtained from the scanning radiometer instruments 
    on Earth Radiation Budget Experiment.  For details on the ERBE satellites, 
    instruments, and data analysis techniques, the user is referred to 
    Barkstrom et al. (1990), Harrison et al. (1990), and Harrison et al. 

                     4.  THEORY OF MEASUREMENTS

The Earth Radiation Budget Experiment (ERBE) is the first Earth radiation 
budget instrument flown simultaneously on multiple satellites to provide the 
necessary temporal sampling for studying the diurnal variations of regional 
broadband radiative parameters over the Earth.  Identical ERBE instruments 
were launched on a dedicated NASA satellite (the Earth Radiation Budget 
Satellite, ERBS) by the Space Shuttle Challenger in October 1984, and two NOAA 
operational satellites launched in December 1984 and November 1986.  The high-
resolution ERBE scanning radiometers were used to determine regional scale 
radiative parameters.  The ERBS obtained 5 years of scanner data; each of the 
NOAA satellites provided about 2 years of scanner data.  

The ERBE data processing system performs three major tasks: 

     (1) Converts telemetry data to calibrated radiation measurements at the 

     (2) Relates the satellite measurements to radiative flux at the top of 
         the Earth's atmosphere using angular dependence models (Smith et al., 

     (3) Averages the measurements over various space and time scales (Brooks 
         et al., 1986).  

The ERBE scanners observe pixels with a nadir size of 35-50 km depending on 
the satellite.  Each 2.5 x 2.5 degree grid box of the original ERBE data 
contained approximately 100 pixels.  These pixels are classified as four 
types:  clear, partly cloudy, mostly cloudy, and overcast.  A maximum 
likelihood estimation technique is used to identify cloud-free scenes 
(Wielicki and Green, 1989).  Clear-sky radiative fluxes at each hour in a grid 
box are calculated as the averaged fluxes of the clear pixels, which are 
converted from radiance measurements through the ERBE angular-directional 
models (Suttles et al., 1988).

                             5.0  EQUIPMENT

5.1 Instrument Description.

    The ERBE scanner (Kopia, 1986) has three spectral channels, 0.2-5.0  m 
    (SW), 5-50  m (LW), and 0.2-50  m (total), to provide consistency checks 
    and redundancy.  The scanner spatial resolution at nadir, the point on the 
    Earth directly below the spacecraft, is about 40 km.  The ERBE scanner is 
    accurate, well calibrated, and stable.  

    5.1.1  Platform.

           ERBE scanning radiometers were flown on three satellites:  ERBS in 
           a 57-deg inclined orbit and NOAA-9 and NOAA-10 in sun synchronous 
           orbits at 14:30 and 07:30 equatorial crossing times, respectively.

    5.1.2  Mission Objectives.

           The goal of ERBE is to understand the radiation balance between the 
           sun, earth, atmosphere, and space, and to establish an accurate 
           baseline data set for detection of climate changes.

    5.1.3  Key Variables.

           Not applicable.

    5.1.4  Principles of Operation.

           Not applicable.

    5.1.5  Instrument Measurement Geometry.

           The ERBE scanner operates in a cross track mode, covering viewing 
           zenith angles from nadir to the limb.  In the processing, only 
           viewing zenith angles less than 70 degrees are considered.  

    5.1.6  Manufacturer of Instrument.

           TRW, Redondo Beach, CA.

5.2  Calibration.

     Ground calibration sources consist of a reference blackbody and an 
     integrating sphere in a vacuum chamber.  In flight, an internal 
     blackbody, evacuated tungsten lamps, and observations of the Sun are used 
     to check the stability and precision of the instruments. 

     5.2.1  Specifications.

            Not available at this revision.


                     Not available at this revision.

     5.2.2  Frequency of Calibration.

            Not available at this revision.

     5.2.3  Other Calibration Information.

            Not available at this revision.

                            6.  PROCEDURE

6.1  Data Acquisition Methods.

     The ERBE scanner data are available from the Langley Distributed Active 
     Archive Center (DAAC) as well as the National Space Science Data Center 
     in Greenbelt, MD.

6.2  Spatial Characteristics.

     ERBS scanner data coverage is from 70S to 70N latitude.  The NOAA 
     satellites have complete global coverage. The original ERBE albedo data 
     had a spatial resolution of 2.5 x 2.5 degree latitude/longitude grid;  
     individual measurements have a resolution of about 40 km at nadir.  For 
     this CD-ROM, the Goddard DAAC has mapped the data onto a 1 degree equal 
     angle lat/lon grid (see section 9.3.1  for details).

     6.2.1  Spatial Coverage.

            The coverage is global.  Data in file are ordered from North to 
            South and from West to East beginning at 180 degrees West and 90 
            degrees North.  Point (1,1) represents the grid cell centered at 
            89.5 N and 179.5 W (see section 8.4).

     6.2.2  Spatial Resolution.

            The data are given in an equal-angle lat/long grid that has a 
            spatial resolution of 1 x 1 degree lat/long.

6.3  Temporal Characteristics.

     6.3.1  Temporal Coverage.

            January 1987 through December 1988.

     6.3.2  Temporal Resolution.

            Monthly mean.

                             7.  OBSERVATIONS

7.1  Field Notes.

     Not applicable.

                            8.  DATA DESCRIPTION

8.1  Table Definition with Comments.

     Not applicable to these data. 

8.2  Type of Data.

|                 8.2.1                  |               |          |          |
|Parameter/Variable Name                 |               |          |          |
|    |               8.2.2               |     8.2.3     |  8.2.4   |  8.2.5   |
|    |Parameter/Variable Description     |Range          |Units     |Source    |
|ERBE_ALB                                |               |          |          |
|    |Clear sky albedo derived from ERBE |min = 0.,      |[unit-    |ERBE      |
|    |data.  Albedo is the fraction of   |max = 1.,      |less]*    |          |
|    |incident solar radiation that a    |fill = -99.00  |          |          |
|    |surface reflects.                  |               |          |          |
|    |                                   |               |          |          |
*Albedo Units are non-dimensional, a fraction between 0 and 1.

8.3  Sample Data Base Data Record.

     Not applicable.

8.4  Data Format.

     The CD-ROM file format is ASCII, and consists of numerical fields of 
     varying length, which are space delimited and arranged in columns and 
     rows.  Each column contains 180 numerical values and each row contain 360 
     numerical values.  

          Grid arrangement

             I  = 1 IS CENTERED AT 179.5W
             J  = 1 IS CENTERED AT 89.5N

             90N - | - - - | - - - | - - - | - -
                   | (1,1) | (2,1) | (3,1) |
             89N - | - - - | - - - | - - - | - -
                   | (1,2) | (2,2) | (3,2) |
             88N - | - - - | - - - | - - - | - -
                   | (1,3) | (2,3) | (3,3) |
             87N - | - - - | - - - | - - - |
                  180W   179W    178W   177W


8.5  Related Data Sets.

     ISCCP-C1 data.

                           9.  DATA MANIPULATIONS
9.1  Formulas.

     For details of the ERBE data processing algorithm, the user is referred 
     to Barkstrom and Smith (1986), Smith et al. (1986), Brooks et al. (1986), 
     Suttles et al. (1988, 1989), and the ERBE S4 User's Guide which is on-
     line at the Langley DAAC. (

     9.1.1  Derivation Techniques/Algorithms.

            Clear-sky albedo is calculated from ERBE measurements.  For a 
            clear-sky shortwave measurement, the clear-sky albedo is defined 
            as the ratio of the outgoing shortwave to the incoming solar flux.  
            For that day, clear-sky albedos at other hours are filled in using 
            the ERBE directional models.  Using only the days with clear-sky 
            measurements, the monthly average clear-sky albedo is determined.  
            The data are mapped onto a 1 x 1 degree grid for this data set.

9.2  Data Processing Sequence.

     Top-of-atmosphere monthly mean albedo is derived from shortwave (0.2-5  
     m) radiances measured by the ERBE scanners (Kopia, 1986) on the ERBS and 
     NOAA-9 spacecraft.  

     9.2.1  Processing Steps and Data Sets.

            See Barkstrom and Smith (1986) and Barkstrom et al. (1989).

     9.2.2  Processing Changes.

            This is the first version of this data set.

9.3  Calculations.

     9.3.1  Special Corrections/Adjustments.

            Below is a description of the re-gridding process done by the 
            Goddard DAAC:

            Physical Lay Out of Original Data:   These data were subset from 
            the GEDEX CD.  Resulting Input data consisted of two files, with 
            each file containing one year worth of data.  Within each file 
            the data were arranged with one data value and corresponding time, 
            latitude, and longitude per line.

            Logical Lay Out of Original Data:   These data were on a 2.5 x 2.5 
            degree grid, with the data starting at 0 longitude, 90 latitude 
            and progressing eastward, and then southward to 360 longitude, -90 
            latitude.  The data at the poles consisted of only one grid value.  
            All other latitude bands consisted of a grid value every 2.5 

               Processing Steps done by the Goddard DAAC:  Regrid each 
               latitude and longitude band of data by implementing the 
               following steps:

               1) Replicated every data value in each latitude band 360 times, 
                  assigning them to a temporary array.  Each of the original 
                  latitude bands had 144 data values, which replicated 360 
                  times produces a temporary array of 51840 data values for 
                  that latitude band.
               2) The first 144 (temporary array) data values are summed and 
                  then divided by the number (144) of original latitude band 
                  values. This was repeated 359 more times, for every 144 
                  (temporary array) data values, in affect performing a linear 
                  interpolation of the data within the latitude band.
               3) Step 1 and 2 were repeated until all latitude bands have 
                  been interpolated.
               4) A test for fill value occurrence was performed.  If fill 
                  value constitutes 50 % or more of contributing values then 
                  assign a fill value to that grid cell, otherwise compute the 
                  average data value for grid cell from only those points 
                  constituting data values.  When assigning fill values, a new 
                  fill value was used, as the existing one was extremely 
               5) The same method, discussed above, was used for regridding 
                  each longitude band of data, except that the number of 
                  replications was 180.  Utilizing the same test for fill 
                  value mentioned above, and the same fill substitution.
               6) The resulting array of data values were then split and 
                  shifted from 0 longitude -> 360 longitude to -180 longitude 
                  -> 180 longitude.
               7) These data were then flipped from -180 longitude, -90 
                  latitude to -180 longitude, 90 latitude.

9.4  Graphs and Plots.

     Not available at this revision.

                              10.  ERRORS

10.1  Sources of Error.

      Errors in clear-sky albedo come from cloud contamination of the scene,  
      instrument errors, sampling errors, and uncertainties in models used in 

10.2  Quality Assessment.

      10.2.1  Data Validation by Source.

              The ERBE clear-sky albedo values are validated by comparison 
              with data from other satellite and aircraft observations of 
              clear scenes.

      10.2.2  Confidence Level/Accuracy Judgment.

              The user is referred to Harrison et al. (1990) for a discussion 
              of ERBE error sources.

      10.2.3  Measurement Error for Parameters and Variables.

              Random error is about 0.01.  Values may also be overestimated 
              slightly due to cloud contamination.  (See Harrison et al., 

      10.2.4  Additional Quality Assessment Applied.

              Not available at this revision.

                                11.  NOTES

11.1  Known Problems with the data.

      There are no known data gaps or other problems.

11.2  Usage Guidance.

      Errors in the polar regions may be larger than those quoted in Sec. 10 
      due to the inability to reliably distinguish between clouds and snow.

11.3  Other Relevant Information.

      The clear sky albedos, estimated from ERBE, generally are a little 
      higher than albedos calculated for a molecular atmosphere with best 
      estimates of surface albedos (over the oceans surface albedos are low 
      and fairly well known).  Some of this difference is likely due to 
      aerosols effect not included in the calculation and some due to the fact 
      that ERBE may designate scenes as clear when they have a small amount of 
      subpixel cloudiness in their view.

                            12.  REFERENCES

12.1  Satellite/Instrument/Data Processing Documentation

      Barkstrom, B. R., 1984.  The Earth Radiation Budget Experiment (ERBE). 
          Bull. Amer. Meteorol. Soc., 65:1170-1185.
      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. Meteorol. Soc., 
      Brooks, D. R., E. F. Harrison, P. Minnis, J. T. Suttles, and R. S. 
          Kandel, 1986.  Development of algorithms for understanding the 
          temporal and spatial variability of the Earth's radiation balance.  
          Rev. Geophys., 24:422-438.
      Harrison, E. F., P. Minnis, and G. G. Gibson, 1983.  Orbital and cloud 
          cover sampling analyses for multisatellite Earth radiation budget 
          experiments.  J. Spacecraft and Rockets, 20:491- 495.
      Kopia, L. P., 1986.  Earth Radiation Budget Experiment scanner 
          instrument. Rev. Geophys., 24:400-406.
      Smith, G. L., R. N. Green, E. Raschke, L. M. Avis, J. T. Suttles, B. A. 
          Wielicki, and R. Davies. 1986.  Inversion methods for satellite 
          studies of the Earth's radiation budget: Development of algorithms 
          for the ERBE mission. Rev. Geophys., 24:407-421.
      Suttles, J. T., R. N. Green, P. Minnis, G. L. Smith, W. F. Staylor, B. 
          A. Wielicki, I. J. Walker, D. F. Young, V. R. Taylor, and L. L. 
          Stowe, 1988. Angular radiation models for Earth-atmosphere system, 
          vol. I, Shortwave radiation. NASA RP-1184.
      Wielicki, B. A. and R. N. Green, 1989.  Cloud identification for ERBE 
          radiative flux retrieval.  J. Appl. Meteorol., 28:1133-1146.

12.2  Journal Articles and Study Reports

      Barkstrom, B. R., E. F. Harrison, and R. B. Lee, 1990.  Earth Radiation 
          Budget Experiment, Preliminary seasonal results.  EOS Transactions, 
          American Geophysical Union, 71, February 27.
      Harrison, E. F., Minnis, P., Barkstrom, B. R., and Gibson, G. G.: 
          Radiation Budget at the Top of the Atmosphere.  Atlas of Satellite 
          Observations Related to Global Change, Edited by R. J. Gurney, J. L. 
          Foster, and C. L. Parkinson, Cambridge University Press, London, 
      Harrison, E. F., P. Minnis, B. R. Barkstrom, V. Ramanathan, R. D. Cess, 
          and G. G. Gibson, 1990a.  Seasonal variation of cloud radiative 
          forcing derived from the Earth Radiation Budget Experiment.  J. 
          Geophys. Res., 95:18687-18703.
      Ramanathan, V., B. R. Barkstrom, and E. F. Harrison, 1989a.  Climate and 
          the Earth's radiation budget.  Physics Today, May, 22-32.
      Ramanathan, V., R. D. Cess, E. F. Harrison, P. Minnis, B. R. Barkstrom, 
          E. Ahmad, and D. Hartmann, 1989b.  Cloud-radiative forcing and 
          climate: Results from the Earth Radiation Budget Experiment.  
          Science, 243:57-63.
      Zhang, M. H., R. D. Cess, T. Y. Kwon, and M. H. Chen, 1994.  Approaches 
          of comparison for clear-sky radiative fluxes from general 
          circulation models with Earth Radiation Budget Experiment data.  J. 
          Geophys. Res., 99:5515-5523.

12.3  Archive/DBMS Usage Documentation.

      Contact the EOS Distributed Active Archive Center (DAAC) at NASA Goddard 
      Space Flight Center (GSFC), Greenbelt Maryland (see Section 13 below).
      Documentation about using the archive or information about access to the 
      on-line information system is available through the GSFC DAAC User 
      Services Office.

                             13.  DATA ACCESS

13.1  Contacts for Archive/Data Access Information.

      GSFC DAAC User Services
      NASA/Goddard Space Flight Center
      Code 902.2
      Greenbelt, MD 20771

      Phone:     (301) 286-3209
      Fax:       (301) 286-1775

13.2  Archive Identification.

      Goddard Distributed Active Archive Center
      NASA Goddard Space Flight Center
      Code 902.2
      Greenbelt, MD 20771

      Telephone:  (301) 286-3209
      FAX:        (301) 286-1775

13.3  Procedures for Obtaining Data.

      Users may place requests by accessing the on-line system, by sending 
      letters, electronic mail, FAX, telephone, or personal visit.

      Accessing the GSFC DAAC Online System:

      The GSFC DAAC Information Management System (IMS) allows users to 
      ordering data sets stored on-line.  The system is open to the public.

      Access Instructions:

      Node name:
      Node number:
      Login example: telnet
      Username:  daacims
      password:  gsfcdaac

      You will be asked to register your name and address during your first

      Ordering CD-ROMs:

      To order CD-ROMs (available through the Goddard DAAC) users should 
      contact the Goddard DAAC User Support Office (see section 13.2).

13.4  GSFC DAAC Status/Plans.

      The ISLSCP Initiative I CD-ROM is available from the Goddard DAAC.


14.1  Tape Products.

      Not available at this revision.
14.2  Film Products.

      Not available at this revision.

14.3  Other Products.

      Not available at this revision.

                       15.  GLOSSARY OF ACRONYMS

CD-ROM            Compact Disk (optical) Read Only Memory
DAAC              Distributed Active Archive Center
EOS               Earth Observing System
ERBE              Earth Radiation Budget Experiment
ERBS              Earth Radiation Budget Satellite
GSFC              Goddard Space Flight Center
ISCCP             International Satellite Cloud Climatology Project
ISLSCP            International Satellite Land Surface Climatology Project
LaRC              Langley Research Center
NASA              National Aeronautics and Space Administration
NOAA              National Oceanic and Atmospheric Administration