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)