BKGRDREF.DOC


                                   1.  TITLE

1.1  Data Set Identification. 

     Background (soil/litter layer) reflectances. 

     (Fixed ; CSU, NASA/GSFC)

1.2  Data Base Table Name.

     Not applicable.

1.3  CD-ROM File Name. 

     \DATA\VEGETATN\BKGRDREF\BKGRDnnn.sfx

     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: BKGRDnnn.sfx, where nnn is the band 
     from which the data was created (e.g. NIR=Near Infrared, VIS=Visible) .  
     The filename extension (.sfx), identifies the data set content for the 
     file (see Section 8.2) and is equal to .BRF for this data set.

1.4  Revision Date Of This Document

     April 5, 1995.

                             2.  INVESTIGATOR(S)

2.1  Investigator(s) Name And Title

     Donald A. Dazlich
     Department of Atmospheric Science
     Colorado State University
     Fort Collins, CO

2.2  Title Of Investigation

     Earth Observing System - Inter-Disciplinary Science
     project (Sellers - Mooney)

2.3  Contacts (For Data Production Information) 

_________________________________________________
              |             Contact 1            |
______________|__________________________________|
2.3.1 Name    |Donald A. Dazlich                 |
2.3.2 Address |Department of Atmospheric Science |
              |Colorado State University         |
      City/St.|Fort Collins CO                   |
      Zip Code|80523                             |
2.3.3 Fax     |(303) 491-8428                    |
2.3.4 Email   |dazlich@erehwon.atmos.            |
              |   colostate.edu                  |
______________|__________________________________|
NOTE: Providing information on these data is not part of my daily routine; 
please read literature and descriptions prior to asking questions. Allow
for some delay in answering questions.

2.4  Requested Form of Acknowledgment

     Thanks to D.A. Dazlich for making the global 1 X 1 degree lat/long 
     background reflectance data available.  This research was funded by the 
     NASA Earth Observing System Inter disciplinary science (EOS-IDS) program, 
     Sellers-Mooney team (contract NAS-531732). Sietse Los provided the biome 
     classification map and the look-up table necessary to make the 
     calculations for this data set.

                             3.  INTRODUCTION

3.1  Objective/Purpose

     The Simple Biosphere model (SiB2) provides a surface albedo for radiative 
     calculations in General Circulation Models (GCMs) (Sellers et al. 1995a). 
     One parameter that contributes to the surface albedo is the background 
     (soil/litter layer) hemispherical reflectance. The background reflectance 
     data set has values that are a function of the biome classification. For 
     desert areas, ERBE July clear sky albedos are inserted.

3.2  Summary of Parameters.

     Background reflectance (visible and near-infrared).

3.3  Discussion.

     Part of the incident solar beam and diffuse shortwave radiation 
     penetrates the vegetation canopy and is reflected by the background 
     (soil/litter layer).  SiB2 uses this background (soil/litter layer) 
     hemispherical reflectance in the calculation of surface albedo for use by 
     GCM radiative parameterizations.  The background hemispherical 
     reflectance is available in two spectral bands, the visible (<.7 microns) 
     and the near IR (> .7 microns). It is assumed to be seasonally invariant 
     and solar zenith angle invariant.  In vegetation areas, background 
     (soil/litter layer reflectances) are assigned by vegetation type (see 
     VEG_CLSS.DOC and Defries and Townshend, 1994a, b).  These values are 
     typical of layers of dead leaves.

     Because of the sparse vegetation cover in deserts, the surface albedo is 
     very nearly the soil reflectance. Desert soil reflectances vary widely 
     regionally (the Australian desert is considerably darker than the 
     Sahara). Therefore, for the desert biomes (biome types 9 and 11) 
     equatorward of 50 degrees latitude, the vegetation-type dependent value 
     was replaced with a clear-sky planetary albedo value as determined by the 
     Earth Radiation Budget Experiment (ERBE). The four-year (1985-1988) July 
     average value was calculated on the 4x5 (CSU, GCM) grid, and that value 
     was inserted in the 1 X 1 desert grid box that was within the 4x5 grid 
     box.  The clear sky albedo was inserted directly into the visible 
     background hemispherical reflectance, and the clear sky albedo times 1.1 
     was inserted into the near IR background hemispherical reflectance. 
     Poleward of 50 degrees latitude, the bare soil values were replaced with 
     those of biome type 12, typical of a dark soil surface.

                        4.  THEORY OF MEASUREMENTS

Not available at this revision.

                            5.  EQUIPMENT

5.1  Instrument Description.

     The Earth Radiation Budget Experiment (ERBE) instrument has flown aboard 
     multiple satellites. The data from ERBE have been analyzed to provide 
     monthly averaged clear-sky and cloudy sky data, in both short and long 
     wavelength intervals. A standard reference on the science background and 
     data sets provided by ERBE may be found in Harrison et al., (1990). A 
     description of the ERBE instrument itself may be found in Kopia (1986).

     5.1.1  Platform.

            See section 5.1.

     5.1.2  Mission Objectives.

            See section 5.1.

     5.1.3  Key Variables.

            See section 5.1.

     5.1.4  Principles of Operation.

            See section 5.1.

     5.1.5  Instrument Measurement Geometry.

            See section 5.1.

     5.1.6  Manufacturer of Instrument.

            See section 5.1.

5.2  Calibration.

            See section 5.1.

     5.2.1  Specifications.

            See section 5.1.

            5.2.1.1  Tolerance.

                     See section 5.1.

     5.2.2  Frequency of Calibration.

            See section 5.1.

     5.2.3  Other Calibration Information.

            See section 5.1.

                              6.  PROCEDURE

6.1  Data Acquisition Methods.

     The background (soil/litter layer) hemispherical reflectance fields were 
     derived from ERBE data, biome classifications (see the Vegetation Map 
     Document, on this CD-ROM) and a review of the ecological literature. See 
     Dorman and Sellers (19890 and Sellers et al (1995b).

6.2  Spatial Characteristics 

     6.2.1  Spatial Coverage 

            The coverage is global.  Data in each 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).

            The background (soil/litter layer) hemispherical reflectance data 
            value coverage is between latitudes of 75 degrees North and South.  
            Latitudes higher than 75 degrees (North or South) are filler and 
            equal zero.  Data for these regions were not available in the 
            GIMMS continental data set.  The calculation of background 
            hemispherical reflectance is made for all vegetated land points 
            and deserts (no permanent ice cover), as defined by the biome 
            classification scheme (see VEG_CLSS.DOC).

     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. 

     Time invariant.

     6.3.1  Temporal Coverage.

            Not applicable.

     6.3.2  Temporal Resolution.

            Not applicable.

                            7.  OBSERVATIONS

7.1  Field Notes.
 
     Not applicable.
 
                            8.  DATA DESCRIPTION
 
8.1  Table Definition With Comments.

     Not applicable.

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   |
--------------------------------------------------------------------------------
|BACKGROUND_REFLECTANCE_VIS.             |               |           |Donald A.|
|    |Visible background hemispherical   |min = 0.1 $    |[Unitless]*|Dazlich  |
|    |reflectance is the fraction of     |max = 0.4 $    |           |         |
|    |incident visible (0.4 - 0.7        |               |           |         |
|    |microns) radiation that is         |               |           |         |
|    |reflected by the soil/litter layer |               |           |         |
|    |surface.                           |               |           |         |
|    |                                   |               |           |         |
--------------------------------------------------------------------------------
|BACKGROUND_REFLECTANCE_NIR              |               |           |Donald A.|
|    |NIR background hemispherical       |min = 0.150 $  |[Unitless]*|Dazlich  |
|    |reflectance, is the fraction of    |max = 0.419 $  |           |         |
|    |incident Near Infrared (0.7 - 1.0  |               |           |         |
|    |microns) radiation that is         |               |           |         |
|    |reflected by the soil/litter layer |               |           |         |
|    |surface.                           |               |           |         |
|    |                                   |               |           |         |
--------------------------------------------------------------------------------
$The minimum and maximum ranges are for vegetated land surface, forest and 
 desert respectively. The ranges are approximations. The potential range is 0 
 to 1. 
*Background (soil/litter layer) Hemispherical Reflectance Units are a non-
 dimensional 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

             ARRAY(I,J)
             I  = 1 IS CENTERED AT 179.5W
             I INCREASES EASTWARD BY 1 DEGREE
             J  = 1 IS CENTERED AT 89.5N
             J INCREASES SOUTHWARD BY 1 DEGREE

             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

            ARRAY(360,180)

8.5  Related Data Sets 
 
     1 X 1 degree Surface Albedo, Donald A Dazlich (on this CD-ROM). 
     1 X 1 degree Normalized Difference Vegetation Index (NDVI) global data 
           (on this CD-ROM).
     1 X 1 degree Fourier based adjustment, solar zenith angle correction, 
           interpolation of missing data and reconstruction of evergreen 
           broadleaf land cover types (tropics), FASIR - NDVI data (on this 
           CD-ROM).
     1 X 1 degree fraction of photosynthetic active radiation absorbed by the 
           vegetation canopy (FPAR) monthly global data (on this CD-ROM). 
     1 X 1 degree leaf area index (LAI) global data (on this CD-ROM).
     1 X 1 degree Greenness global data (on this CD-ROM).
     1 X 1 degree roughness length (ZO) monthly global data (on this CD-ROM).
     1 X 1 degree vegetation classification map, Dorman and Sellers (1989), 
           Sellers et al. (1995b), on this CD-ROM.

     Also see section 8.5 (Related Data Sets) in the NDVI document.

                           9.  DATA MANIPULATIONS

9.1  Formulas.

     9.1.1  Derivation Techniques/Algorithms.

            The background hemispherical reflectance data set has values that 
            are a function of the biome classification. For desert biomes, 
            ERBE July clear sky albedos are inserted. From a map of the biome 
            types and a look-up table (See VEG_CLSS.DOC section 11.3, on this 
            CD-ROM), a background reflectance in each spectral interval is 
            assigned for each vegetated 1 X 1 grid box, with the following 
            modification. For the desert biomes (biome types 9 and 11) 
            equatorward of 45 degrees latitude, the look-up table value was 
            replaced with a clear-sky planetary albedo value as determined by 
            the Earth Radiation Budget Experiment (ERBE). The Himalayas are 
            given special treatment: as the ERBE value give snow reflectance 
            in this region, rather than substrate reflectance. The original 
            biome-dependent background hemispherical reflectance are retained. 
            The four-year (1985-1988) July average value was calculated on the 
            4x5 (CSU GCM) grid, and that value was inserted in the 1*1 desert 
            grid box that was within the 4x5 grid box. The clear sky albedo 
            was inserted directly into the visible soil reflectance, and the 
            clear sky albedo times 1.1 was inserted into the near IR soil 
            reflectance.

9.2  Data Processing Sequence.

     9.2.1  Processing Steps and Data Sets.

            See section 9.1.1.

     9.2.2  Processing Changes.

            See section 9.1.1.

9.3  Calculations.

     9.3.1  Special Corrections/Adjustments.

            See section 9.1.1.

9.4  Graphs and Plots.

     None.

                                 10.  ERRORS

10.1  Sources of Error.

      Errors arise from:

      (1) The soil and litter background reflectance assigned to each 
          vegetation type in SiB2 are based on a review of the ecological 
          literature, see Dorman and Sellers (1989) and Sellers et al (1995b). 
          Obviously, these represent a very small sample of soil and litter 
          background reflectance.

      (2) A number of assumptions about the Bi-directional Reflectance 
          Distributions Functions (BRDF) of the surface and atmospheric 
          transmission are made in the derivation of ERBE clear-sky albedos. 
          Some of these are suspect in areas with extreme BRDF 
          characteristics.

      (3) When ERBE data are 'pasted in' the SiB2 desert areas, the vegetation 
          contributions to the ERBE data are ignored - the ERBE value is 
          assigned into the soil reflectance.

10.2  Quality Assessment.

      10.2.1  Data Validation by Source.

              It is difficult to be quantitative about the likely size of 
              errors in these fields. A rough estimate would be that the 
              reflectances are probably within 5-10% absolute of the area-
              averaged values, judging by the comparisons between the ERBE 
              fields and surface measurements and the few field measurements 
              that have been made.

      10.2.2  Confidence Level/Accuracy Judgment.

              See section 10.2.1.

      10.2.3  Measurement Error for Parameters and Variables.

              See section 10.2.1.

      10.2.4  Additional Quality Assessment Applied.

              See section 10.2.1.

                                 11.  NOTES 

11.1  Known Problems With The Data.

      The bulk of the background reflectance are created by assigning a few 
      field measurements values to an entire biome. This is clearly invalid 
      for biomes with variable backgrounds. Other sources of error are 
      discussed in section 9.

11.2  Usage Guidance. 

      These fields were intended to be used as the background (lower boundary) 
      conditions for canopy radiative transfer models, see the surface albedo 
      product on this CD-ROM. In most places, a very accurate estimate of this 
      reflectance is not required as it makes only a very small contribution 
      to the total surface albedo. In any case, these data should not be seen 
      as at all reliable in vegetated regions or used in point studies without 
      local confirmation of the values.

      It should be emphasized that the data are intended as lower boundary 
      conditions. For the forested parts of the world, litter layer values are 
      assigned as the actual soil surface is normally covered by litter.
 
11.3  Other Relevant Information.

      Not available at this revision.

                             12.  REFERENCES 

12.1  Satellite/Instrument/Data Processing Documentation.

      Harrison, E.F., P. Minnis, B.R. Barkstrom, V. Ramanathan, R.D. Cess, and 
          G.G. Gibbson, 1990. Seasonal variation of cloud radiative forcing 
          derived from the Earth Radiation Budget Experiment. Journal of 
          Geophysical Research, 95:18,687-18703.
      Kopia, L.P., 1986. Earth Radiation Budget Experiment scanner instrument, 
          Rev. Geophys., 21:400-406.

12.2  Journal Articles and Study Reports.

      DeFries, R. S. and J. R. G. Townshend, 1994a. NDVI-derived land 
           cover classification at global scales. International Journal of 
           Remote Sensing, 15:3567-3586. Special Issue on Global Data Sets.
      DeFries, R. S. and J. R. G. Townshend, 1994b. Global land cover:
           comparison of ground-based data sets to classifications with AVHRR 
           data. In Environmental Remote Sensing from Regional to Global 
           Scales, edited by G. Foody and P. Curran, Environmental Remote 
           Sensing from Regional to Global Scales. (U.K.: John Wiley and 
           Sons).
      Dorman, J.L., and Sellers, P.J., 1989. A Global climatology of albedo, 
          roughness length and stomatal resistance for atmospheric general 
          circulation models as represented by the simple biosphere model 
          (SiB). Journal of Applied Meteorology, 28:833-855.
      Sellers, P.J., D.A. Randall, C.J. Collatz, J.A. Berry, C.B. Field, D.A. 
          Dazlich, C. Zhang, and C.D. Collelo, 1995a. A revised land surface 
          parameterization (SiB2) for atmospheric GCMs. Part 1: Model 
          formulation. Submitted to Journal of Climate.
      Sellers, P.J., S.O. Los, C.J. Tucker, C.O. Justice, D.A. Dazlich, G.J. 
         Collatz, and D.A. Randall, 1995b. A revised land surface 
         parameterization (SiB2) for atmospheric GCMs. Part 2: The generation 
         of global fields of terrestrial biophysical parameters from satellite 
         data. Submitted to Journal of Climate.

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
      Internet:  daacuso@eosdata.gsfc.nasa.gov

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
      Internet:   daacuso@eosdata.gsfc.nasa.gov

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:  daac.gsfc.nasa.gov
      Node number: 192.107.190.139
      Login example: telnet daac.gsfc.nasa.gov
      Username:  daacims
      password:  gsfcdaac

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

      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-ROMs are available from the Goddard DAAC.

                   14.  OUTPUT PRODUCTS AND AVAILABILITY

14.1  Tape Products

      None.

14.2  Film Products 

      None.

14.3  Other Products 

      None.

                         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
GCM          General Circulation Model of the atmosphere
GIMMS        Global Inventory Monitoring and Modeling Studies at NASA GSFC
GSFC         Goddard Space Flight Center
IDS          Inter disciplinary Science
ISLSCP       International Satellite Land Surface Climotology Project
NASA         National Aeronautics and Space Administration
SiB2         Simple Biosphere model (Sellers et al 1995a)