ROUGHNESS.DOC
1. TITLE
1.1 Data Set Identification.
Roughness length (Zo).
Zo (Monthly ; NASA/GSFC)
1.2 Data Base Table Name.
Not applicable.
1.3 CD-ROM File Name.
\DATA\VEGETATN\ROUGHNSS\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 .ZOL 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., 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.
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 X 1 degree roughness length (Zo) data set was compiled to calculate
the energy and water exchange between the biosphere and atmosphere with
the simple biosphere model. (SiB2) (Sellers et al. (1995a). With the SiB2
calculations the effect of vegetation on climate can be incorporated in a
General Circulation Model (GCM) of the atmosphere.
3.2 Summary of Parameters
Z0: (Z subscript naught) Roughness length
see also section 3.3
3.3 Discussion.
Roughness length is calculated using a one-dimensional, first-order
turbulent transfer model (Sellers et al 1989, 1995a). The parameters
involved in calculating Zo are:
LAI = leaf area index m^2 m^-2
Cd = leaf drag coefficient m
Z2 = canopy top height m
Z1 = canopy base height m
Zs = soil/litter layer roughness length m
4. THEORY OF MEASUREMENTS
The first-order closure model of Sellers et al. (1989, 1995a) is applied
repeatedly to the vegetation properties subset of morphological parameters,
e.g., vegetation height, leaf morphology, etc., to create look-up tables of
roughness length Zo, for each vegetation type. The model is cycled to produce
values of this parameter for each vegetation type for leaf area indices
ranging from [0] to [8.0] in [0.5] increments. This look-up table (section
9.2.1) is relationally combined with the LAI fields and land cover map
(VEG_CLSS.VGC) to produce 1 X 1 degree monthly fields of Zo. Linear
interpolation is used between the look-up table values.
5. EQUIPMENT
5.1 Instrument Description.
See NDVI and VEG_CLSS.VGC documents on this CD-ROM.
5.1.1 Platform.
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 Zo data set is calculated from the 1 X 1 degree global
VEG_CLSS.VGC data set, the LAI data and a look-up table (section 9.2.2).
6.2 Spatial Characteristics.
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.
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 |
--------------------------------------------------------------------------------
|ROUGHNESS LENGTH | | | |
| |The aerodynamic roughness length |Min = 02 $ |[m] |Sellers |
| |(Zo), is defined as the height |Max = 2.99 $ | |et al |
| |above the ground where the wind | | |(1994a)* |
| |speed becomes zero due to the | | | |
| |effects of vegetation. | | | |
| | | | | |
--------------------------------------------------------------------------------
$ The range in roughness values is dependent on vegetation class, see table in
section 92. A minimum value of 0.02 has been inserted into the ROUCHNESS
data sets for regions (Antarctic, Greenland...) that are classified as
missing data in the NDVI data set (see NDVI.DOC). Note: some of these
regions have no vegetation.
* The roughness data was derived from 1 X 1 degree global LAI data set and
land cover data set discussed Sellers et al (1994, 1995b).
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 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 snow free Surface Albedo monthly global data (on this
CD-ROM).
1 X 1 degree land cover map (VEG_CLSS.VGC), on this CD-ROM.
Also see section 8.5 (Related Data Sets) in the NDVI document.
9. DATA MANIPULATIONS
9.1 Formulas.
Data have been adjusted using both formulas and rules, the
description of the complete procedure is provided under 9.2.
9.1.1 Derivation Techniques/Algorithms.
See section 9.2
9.2 Data Processing Sequence.
In adition to the description given below see the description in (Sellers
et al 1994, 1995b)
Two data sets and a lookup-table (below) are used for the calculation of
roughness length.
1. 1 X 1 degree LAI data set
2. land cover classification (VEG_CLSS.VGC)
3. The turbulent transfer model is run off-line repeatedly for different
vegetation types over a range of Leaf Area Index values to generate a
lookup table (see below).
Specification of Zo is done by linear interpolation of roughness length
values that are known for a particular LAI and vegetation type (see
below).
For example,
given LAI = 3.25, vegetation type = 1 (broadleaf evergreen),
Zo = (3.25 - 3.0)*(2.99 - 2.99) + 2.99 = 2.99
===========================================================================
vegetation classes
===========================================================================
LAI 1 2 3 4 5 6 7 8 9 10 11 12
0.5 0.02 0.02 0.02 0.02 0.02 0.02 0.02 0.02 0.02 0.02 0.02 0.02
1.0 1.89 0.45 0.56 0.65 0.68 0.12 0.12 0.12 0.06 0.08 0.12 0.12
1.5 2.50 0.62 0.78 0.88 0.91 0.13 0.13 0.13 0.06 0.08 0.13 0.13
2.0 2.80 0.72 0.91 1.00 1.03 0.13 0.13 0.13 0.06 0.08 0.13 0.13
2.5 2.94 0.79 0.99 1.08 1.10 0.13 0.13 0.13 0.07 0.08 0.13 0.13
3.0 2.99 0.83 1.04 1.12 1.14 0.13 0.13 0.13 0.07 0.08 0.13 0.13
3.5 2.99 0.86 1.09 1.16 1.17 0.13 0.13 0.13 0.07 0.08 0.13 0.13
4.0 2.97 0.87 1.11 1.18 1.19 0.13 0.13 0.13 0.07 0.08 0.13 0.13
4.5 2.92 0.89 1.13 1.19 1.20 0.13 0.13 0.13 0.07 0.08 0.13 0.13
5.0 2.87 0.90 1.15 1.20 1.21 0.13 0.13 0.13 0.07 0.08 0.13 0.13
5.5 2.81 0.90 1.16 1.21 1.21 0.13 0.13 0.13 0.07 0.08 0.13 0.13
6.0 2.74 0.90 1.17 1.21 1.21 0.13 0.13 0.13 0.07 0.08 0.13 0.13
6.5 2.68 0.90 1.17 1.21 1.21 0.12 0.12 0.12 0.07 0.08 0.12 0.12
7.0 2.62 0.90 1.18 1.21 1.21 0.12 0.12 0.12 0.07 0.08 0.12 0.12
7.5 2.56 0.90 1.18 1.21 1.21 0.12 0.12 0.12 0.07 0.08 0.12 0.12
8.0 2.5 0.90 1.18 1.21 1.20 0.12 0.12 0.12 0.07 0.08 0.12 0.12
8.5 2.47 0.90 1.18 1.21 1.20 0.12 0.12 0.12 0.07 0.08 0.12 0.12
9.0 2.47 0.90 1.18 1.21 1.20 0.12 0.12 0.12 0.07 0.08 0.12 0.12
Roughness length (Z0) lookup table as a function of vegetation type and
LAI. For more information on the vegetation classes, see the
documentation for VEG_CLSS.VGC.
9.2.1 Processing Steps and Data Sets.
See section 9.2.
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
Known errors are those inherited from other data sets, first order
dependence on errors in VEG_CLSS.VGC, second order dependence on
errors in leaf area index (see NDVI, FASIR and FPAR, LAI and
VEG_CLSS.VGC data sets).
10.2 Quality Assessment.
10.2.1 Data Validation by Source.
A rigorous verification of Zo has still to be done (Sellers et
al 1994, 1995b).
10.2.2 Confidence Level/Accuracy Judgment.
The roughness length data have a first order dependency on land
cover type, and depend only to a minor degree on leaf area
index. Hence, the values will be very sensitive towards errors
in the vegetation classification and the inability to address
mixtures of types with a land cover classification. Especially
in dense woodlands (included in type 6) roughness lengths are
low, whereas in reality they can approach values of the
evergreen broadleaf forests Additionally, it is assumed that
each grid cell is uniformly covered by one vegetation class and
LAI value. In practice, heterogeneity's combine in a non-linear
way to yield different aggregate roughness values than those
arrived at by simple averaging, as in this case.
10.2.3 Measurement Error for Parameters and Variables.
See VEG_CLSS.VGC and above.
10.2.4 Additional Quality Assessment Applied.
Not available at this revision.
11. NOTES
11.2 Usage Guidance.
Roughness length fields should only be used with extreme caution.
11.3 Other Relevant Information.
Not available at this revision.
12. REFERENCES
12.1 Satellite/Instrument/Data Processing Documentation.
Not applicable.
12.2 Journal Articles and Study Reports.
Los, S.O., C.O. Justice, C.J. Tucker, 1994. A global 1 by 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., W.J. Shuttleworth, J.L. Dorman, A. Dalcher, J.M. Roberts,
1989. Calibrating the Simple Biosphere model for Amazonian tropical
forest using field and remote sensing data. Part I: Average
calibration with field data, Journal of Applied Meteorology. 28:727-
759.
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., 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-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 Destributed Active Archive Center
EOS Earth Observing System
GAC Global Area Coverage
GCM General Circulation Model of the atmosphere
FASIR (NDVI) Fourier Adjusted, Solar zenith angle correction,
Interpolation (of missing data during winter), and
Reconstruction of NDVI over tropical forests.
FPAR Fraction of Photosynthetic Active Radiation absorbed by
green vegetation
GIMMS Global Inventory Monitoring and Modeling Studies at
NASA GSFC
GSFC Goddard Space Flight Center
GVI Global Vegetation Index
IDS Inter disciplinary Science
IFOV Instantaneous Field Of View
ISLSCP International Satellite Land Surface Climotology 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
pixel Picture element
SiB2 Simple Biosphere model (Sellers et al 1995a)
SR Simple Ratio