FPAR.DOC


                                 1.  TITLE

1.1  Data Set Identification.

     Fraction of photosynthetic active radiation absorbed by the green 
     vegetation canopy (FPAR).

     FPAR (Monthly ; NASA/GSFC)

1.2  Data Base Table Name.

     Not applicable.

1.3  CD-ROM File Name. 

     \DATA\VEGETATN\FPAR\YyyMmm.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: YyyMmm.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 .FPA for this 
     data set.

1.4  Revision Date Of This Document.

     April 5, 1995

                            2.  INVESTIGATOR(S)

2.1  Investigator(s) Name And Title.

     Sietse O. Los, Piers J. Sellers
     Biospheric Sciences Branch
     NASA Goddard Space Flight Center

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    |Sietse O. Los                    |
2.3.2 Address |Biospheric Sciences Branch       |
              |code 923                         |
              |NASA Goddard Space Flight Center |
      City/St.|Greenbelt MD                     |
      Zip Code|20771                            |
2.3.3 Fax     |(301) 286-1757                   |
2.3.4 Email   |Sietse@Jello.gsfc.nasa.gov       |
______________|_________________________________|
NOTE: Providing information on these data is not part of my daily routine; 
      Please read literature and descriptions first. Allow for some delay in 
      my response.

**********************************************************
* FOR GENERAL QUESTIONS REGARDING THE DATA CONTACT THE   *
*             GODDARD DAAC (SEE SECTION 13).             *
**********************************************************

2.4. Requested Form of Acknowledgment.

     Please cite the following publications when ever these data are used:

      Sellers, P.J., S.O. Los, C.J. Tucker, C.O. Justice, D.A. Dazlich, G.J. 
         Collatz, and D.A. Randall, 1994. A global 1 by 1 degree NDVI data set 
         for climate studies. Part 2: The generation of global fields of 
         terrestrial biophysical parameters from the NDVI.  International 
         Journal of Remote Sensing, 15(17):3519-3545.
      Sellers, P.J., S.O. Los, C.J. Tucker, C.O. Justice, D.A. Dazlich, G.J. 
         Collatz, and D.A. Randall, 1995. 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.

     ACKNOWLEDGMENTS

     This research was funded by the NASA Earth Observing System Inter
     disciplinary science (EOS-IDS) program, Sellers-Mooney team.

                             3.  INTRODUCTION

3.1  Objective/Purpose.

     The 1*1 degree FPAR data set is an essential variable for the calculation 
     of photosynthesis, and the energy and water exchange between the Earth's 
     surface (in particular of vegetation) and the lower boundary layer of the 
     atmosphere. It also serves as an intermediate variable to calculate Leaf 
     area index (LAI), Roughness length (Z0), green fraction of total leaves 
     (greenness) and albedo (Sellers et al 1994, 1995). Note that FPAR refers 
     to the fraction of PAR absorbed by the green portion only of the canopy.

3.2  Summary of Parameters.

     FPAR: Fraction of Photosynthetic Active Radiation absorbed by green part 
     of vegetation.

3.3  Discussion.

     The derivation of FPAR fields depends on a near-linear relationship 
     between FPAR and Simple Ratio (a transformation of the NDVI) that was 
     found in theoretical studies by e.g. Sellers (1985) for a vegetation 
     canopy over a dark soil background. This near-linear relationship was 
     confirmed in studies during the FIFE field campaign for a grassland 
     (Hall et al 1992). The FPAR - SR relationship is driven by the very 
     different optical properties of green leaves in the red (high absorption) 
     and infrared (high reflection) bands. SR or NDVI relates less well to the 
     FPAR of the total canopy, the relationship is fairly strong for the 
     "green" FPAR.  In some cases (bright soil background), the NDVI - FPAR 
     relationship was shown to be near-linear, rather than the SR-FPAR 
     relationship. Results from other large remote sensing experiments will be 
     needed to obtain further information on this relationship. See also 
     Sellers 1985, Hall et al 1992, Sellers et al 1994, 1995 and papers quoted 
     from these.

                          4.  THEORY OF MEASUREMENTS

For the calculation we assume a linear relationship between SR and FPAR.  We 
further assume that the 98 percentile of the NDVI distribution of a vegetation 
type reflects fully "green" conditions, and an FPAR value close to maximum 
(0.95). For certain vegetation types, in general the short vegetation classes, 
it is not reasonable to make this assumptions, because these classes occur in 
environments that are sub-optimal for maximum vegetation development. We 
therefore merged the short vegetation types with classes that had a similar 
sza - P98 relationship (see FASIR document). Thus class 8 (shrubs and ground 
cover) was merged with class 1 and 6, we applied  the 98 % values of classes 
2-5 combined to class 10 (tundra), and we used the 98 % values of agriculture 
for the short types 7 (grassland, 9 (ground cover over bare soil), and 11 
(bare soil) (see Sellers et al 1994). We used one minimum NDVI value for all 
cover types. This value is the 2 percentil of the NDVI distribution of classes 
9 (shrubs with bare soil) and 11 (bare soil).

                                5.  EQUIPMENT

5.1  Instrument Description.

     See the NDVI document.

     5.1.1  Platform (Satellite, Aircraft, Ground, Person...).

            See the NDVI document.

     5.1.2  Mission Objectives.

            See the NDVI document.

     5.1.3  Key Variables.

            See the NDVI document.

     5.1.4  Principles of Operation.

            See the NDVI document.

     5.1.5  Instrument Measurement Geometry .

            See the NDVI document.

     5.1.6  Manufacturer of Instrument.

            See the NDVI document.

5.2  Calibration.

     See the NDVI document.

     5.2.1  Specifications.

            See the NDVI document.

            5.2.1.1  Tolerance.

                     See the NDVI document.

     5.2.2  Frequency of Calibration.

            See the NDVI document.

     5.2.3  Other Calibration Information.

            See the NDVI document.

                             6.  PROCEDURE

6.1  Data Acquisition Methods.

     The 1 X 1 degree FPAR data set is calculated from 1 X 1 degree global 
     FASIR - NDVI data set and the VEG_CLSS.VGC data.

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).

     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

                            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    |
--------------------------------------------------------------------------------
|FPAR                                   |            |              |          |
|    |fraction of photosynthetic active |Min 0.001   |[Unitless]*   |Sellers et|
|    |radiation absorbed by the green   |Max 0.95    |              |(1994a)   |
|    |vegetation canopy.                |            |              |          |
|    |                                  |            |              |          |
--------------------------------------------------------------------------------
*FPAR Units are non-dimensional, a fraction ranging from 0.001 to 0.95.  A 
 minimum value of 0.001 has been inserted into the FPAR data sets for regions 
 (Antarctic, Greenland...) that are classified as missing data in the NDVI 
 data set (see NDVI.DOC).

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 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 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 snow free SURFACE ALBEDO monthly global data (on this 
           CD-ROM).
     1 X 1 degree vegetation classification map (Dorman and Sellers 1989, 
           Nobre et al. 1991), on this CD-ROM.

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

                          9.  DATA MANIPULATIONS

9.2  Data Processing Sequence.

     (Sellers et al 1994, 1995)

     9.2.1  Processing Steps and Data Sets.

            Two data sets are used for the calculation of
            FPAR.

            1. 1*1 degree FASIR- NDVI data set (FASIR87)
            2. land cover classification (VEG_CLSS.VGC)

            calculation of FPAR from FASIR data

                    FPAR = (0.95-0.001)(SR - SR02)/(SR98 - SR02) + 0.001
                    truncate such that 0.001 <= FPAR <= 0.950

            where
                    SR = (1+NDVI)/(1-NDVI) (is the simple ratio
                    NDVI = FASIR NDVI
                    SR98 = 98 % SR of a particular land cover class for 
                           overhead sun SR02 =  2 % SR of desert (bare soil) 
                           for overhead sun

            SR98 and SR02 values are calculate from NDVI 98% and 02% in the 
            table.

            IV refers to land cover class, see Documentation VEG_CLSS.VGC

             ==========================
             vegetation parameters
             ==========================
             1    0.618          0.034
             2    0.686          0.034
             3    0.686          0.034
             4    0.686          0.034
             5    0.686          0.034
             6    0.618          0.034
             7    0.630          0.034
             8    0.618          0.034
             9    0.630          0.034
             10   0.686          0.034
             11   0.630          0.034
             12   0.630          0.034
             IV   NDVI98         NDVI02  

             Table with NDVI98 and NDVI2 values for each vegetation type

     9.2.2  Processing Changes.

            Not available at this revision.

9.3  Calculations.

     9.3.1  Special Corrections/Adjustments.

            Not available at this revision.

9.4  Graphs and Plots.

     Not available at this revision.

                              10.  ERRORS

10.1  Sources of Error

      1. Errors inherited from other data sets (see NDVI and FASIR - NDVI)

      2. Errors in classification (see VEG_CLSS.VGC).

      3. Assumption that 2% and 98% values for a vegetation type represent 
         conditions with FPAR of 0.001 and 0.95.

      4. Assumption that SR and FPAR relationship is linear, this linear 
         relationship is supported by model studies that use a dark soil 
         background. For a light soil background, it is the relationship 
         between NDVI and FPAR that appears to be more linear, rather than the 
         SR - FPAR relationship.

10.2  Quality Assessment.

      10.2.1  Data Validation by Source.

              A rigorous verification of FPAR has still to be done and will be 
              subject of future studies (Sellers et al 1994, 1995).

      10.2.2  Confidence Level/Accuracy Judgment.

              See the NDVI document, FASIR document and section 10.2.1 in this 
              document.

      10.2.3  Measurement Error for Parameters and Variables.

              See the FASIR Document.

      10.2.4  Additional Quality Assessment Applied.

              Not available at this revision.

                                 11.  NOTES

11.1  Known Problems With The Data.

      Related to products from which FPAR is derived (FASIR-NDVI, 
      VEG_CLSS.VGC, NDVI) as well as to assumptions used for the calculation 
      of FPAR.

11.2  Usage Guidance.

      FPAR presents generalized patterns which may result in poor 
      representations of a specific locale

11.3  Other Relevant Information.

      Not available at this revision.

                             12.  REFERENCES

12.1  Satellite/Instrument/Data Processing Documentation.

      Not available at this revision.

12.2  Journal Articles and Study Reports.

      Hall, F.G, Huemmrich, K.F., Goetz, S.J., Sellers, P.J., Nickeson, J.E.,
          1992, Satellite remote sensing of surface energy balance: Success, 
          failures and unresolved issues in FIFE, J. Geophysical Res. 97(D17):
          19061-19089.
      Los, S.O.,  C.O. Justice, C.J. Tucker, 1994. A global 1*1 degree NDVI 
          data set for climate studies derived from the GIMMS continental NDVI 
          data. International Journal of Remote Sensing, 15(17):3493-3518. 
      Sellers, P.J., 1985. Canopy reflectance, photosynthesis and
          transpiration. International Journal of Remote Sensing, 16:1335-
          1372.
      Sellers, P.J., S.O. Los, C.J. Tucker, C.O. Justice, D.A. Dazlich, G.J. 
          Collatz, and D.A. Randall, 1994. A global 1 by 1 degree NDVI data 
          set for climate studies. Part 2: The generation of global fields of 
          terrestrial biophysical parameters from the NDVI. International 
          Journal of Remote Sensing, 15(17):3519-3545.
      Sellers, P.J., S.O. Los, C.J. Tucker, C.O. Justice, D.A. Dazlich, G.J. 
          Collatz, and D.A. Randall, (1995, submitted). A revised land 
          surface parameterization (SiB2) for atmospheric GCMs. Part 2: The 
          generation of global fields of terrestrial biophysical parameters 
          from satellite data. 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-ROM is 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

AVHRR        Advanced Very High Resolution Radiometer
CD-ROM       Compact Disk (optical), Read Only Memory
DAAC         Distributed Active Archive Center
EOS          Earth Observing System
GAC          Global Area Coverage
GCM          General Circulation Model of the atmosphere
GIMMS        Global Inventory Monitoring and Modeling Studies at NASA GSFC
GSFC         Goddard Space Flight Center
GVI          Global Vegetation Index
IDS          Interdisciplinary Science
ISLSCP       International Satellite Land Surface Climatology Project
LAC          Local Area Coverage
LAI          Leaf Area Index
NASA         National Aeronautics and Space Administration
NDVI         Normalized Difference Vegetation Index
NOAA         National Oceanographic and Atmospheric Administration
FPAR         Fraction of Photosynthetic Active Radiation absorbed by 
             green vegetation
SiB2         Simple Biosphere model (Sellers et al 1995)
SR           Simple Ratio