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