ERBE_ALB.DOC
1. TITLE
1.1 Data Set Identification.
ERBE S4 Clear-Sky Albedo.
(Monthly Mean Albedo ; NASA/LaRC)
1.2 Data Base Table Name.
Not applicable.
1.3 CD-ROM File Name.
\DATA\RADIATN\ERBE_ALB\ERYyyMmm.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: ERYyyMmm.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 .ALB for this
data set.
1.4 Revision Date Of This Document.
April 5, 1995.
2.1 Investigator(s) Name and Title.
Dr. Bruce R. Barkstrom
Radiation Sciences Branch
NASA Langley Research Center
2.2 Title of Investigation.
Earth Radiation Budget Experiment.
2.3 Contacts (For Data Production Information).
_____________________________________________________________________
| Contact 1 | Contact 2 |
______________|__________________________|___________________________|
2.3.1 Name |Mr. Edwin F. Harrison |Dr. Bruce R. Barkstrom |
2.3.2 Address |Mail Stop 420 |Mail Stop 420 |
|Radiation Sciences Branch |Radiation Sciences Branch |
|NASA/LaRC |NASA/LaRC |
City/St.|Hampton, VA |Hampton, VA |
Zip Code|23681-0001 |23681-0001 |
2.3.3 Tel. |(804) 864-5663 |(804) 864-5656 |
2.3.4 Email |e.f.harrison@larc.nasa.gov|b.r.barkstrom@larc.nasa.gov|
______________|__________________________|___________________________|
_______________________________________
| Contact 3 |
______________|________________________|
2.3.1 Name |Mr. David F. Young |
2.3.2 Address |Lockheed Engineering |
|& Sciences Co. |
|144 Research Drive |
City/St.|Hampton, VA |
Zip Code|23666 |
2.3.3 Tel. |(804) 766-9674 |
2.3.4 Email |d.f.young@larc.nasa.gov |
______________|________________________|
2.4 Requested Form of Acknowledgment.
Please cite the following publication when these data are used:
Barkstrom, B. R., E. F. Harrison, and R. B. Lee, 1990. Earth Radiation
Budget Experiment, Preliminary seasonal results. EOS Transactions,
American Geophysical Union, 71, February 27.
3. INTRODUCTION
3.1 Objective/Purpose.
The goals of the Earth Radiation Budget Experiment (ERBE) are (1) to
understand the radiation balance between the Sun, Earth, atmosphere, and
space and (2) to establish an accurate, long-term baseline data set for
detection of climate changes. Earth radiation budget (ERB) data are
fundamental to the development of realistic climate models and to the
understanding of natural and anthropogenic perturbations of the climate
system. As part of ERBE, measurements of broadband shortwave radiation
reflected from the Earth-atmosphere system were obtained, from which
albedo values were calculated. In addition, values from scenes determined
to be free of clouds were analyzed separately and clear-sky albedos were
derived.
3.2 Summary of Parameters.
For this study, only the clear-sky albedos are included.
3.3 Discussion.
Clear-sky albedos were obtained from the scanning radiometer instruments
on Earth Radiation Budget Experiment. For details on the ERBE satellites,
instruments, and data analysis techniques, the user is referred to
Barkstrom et al. (1990), Harrison et al. (1990), and Harrison et al.
(1993).
4. THEORY OF MEASUREMENTS
The Earth Radiation Budget Experiment (ERBE) is the first Earth radiation
budget instrument flown simultaneously on multiple satellites to provide the
necessary temporal sampling for studying the diurnal variations of regional
broadband radiative parameters over the Earth. Identical ERBE instruments
were launched on a dedicated NASA satellite (the Earth Radiation Budget
Satellite, ERBS) by the Space Shuttle Challenger in October 1984, and two NOAA
operational satellites launched in December 1984 and November 1986. The high-
resolution ERBE scanning radiometers were used to determine regional scale
radiative parameters. The ERBS obtained 5 years of scanner data; each of the
NOAA satellites provided about 2 years of scanner data.
The ERBE data processing system performs three major tasks:
(1) Converts telemetry data to calibrated radiation measurements at the
instruments.
(2) Relates the satellite measurements to radiative flux at the top of
the Earth's atmosphere using angular dependence models (Smith et al.,
1986).
(3) Averages the measurements over various space and time scales (Brooks
et al., 1986).
The ERBE scanners observe pixels with a nadir size of 35-50 km depending on
the satellite. Each 2.5 x 2.5 degree grid box of the original ERBE data
contained approximately 100 pixels. These pixels are classified as four
types: clear, partly cloudy, mostly cloudy, and overcast. A maximum
likelihood estimation technique is used to identify cloud-free scenes
(Wielicki and Green, 1989). Clear-sky radiative fluxes at each hour in a grid
box are calculated as the averaged fluxes of the clear pixels, which are
converted from radiance measurements through the ERBE angular-directional
models (Suttles et al., 1988).
5.0 EQUIPMENT
5.1 Instrument Description.
The ERBE scanner (Kopia, 1986) has three spectral channels, 0.2-5.0 m
(SW), 5-50 m (LW), and 0.2-50 m (total), to provide consistency checks
and redundancy. The scanner spatial resolution at nadir, the point on the
Earth directly below the spacecraft, is about 40 km. The ERBE scanner is
accurate, well calibrated, and stable.
5.1.1 Platform.
ERBE scanning radiometers were flown on three satellites: ERBS in
a 57-deg inclined orbit and NOAA-9 and NOAA-10 in sun synchronous
orbits at 14:30 and 07:30 equatorial crossing times, respectively.
5.1.2 Mission Objectives.
The goal of ERBE is to understand the radiation balance between the
sun, earth, atmosphere, and space, and to establish an accurate
baseline data set for detection of climate changes.
5.1.3 Key Variables.
Not applicable.
5.1.4 Principles of Operation.
Not applicable.
5.1.5 Instrument Measurement Geometry.
The ERBE scanner operates in a cross track mode, covering viewing
zenith angles from nadir to the limb. In the processing, only
viewing zenith angles less than 70 degrees are considered.
5.1.6 Manufacturer of Instrument.
TRW, Redondo Beach, CA.
5.2 Calibration.
Ground calibration sources consist of a reference blackbody and an
integrating sphere in a vacuum chamber. In flight, an internal
blackbody, evacuated tungsten lamps, and observations of the Sun are used
to check the stability and precision of the instruments.
5.2.1 Specifications.
Not available at this revision.
5.2.1.1 Tolerance.
Not available at this revision.
5.2.2 Frequency of Calibration.
Not available at this revision.
5.2.3 Other Calibration Information.
Not available at this revision.
6. PROCEDURE
6.1 Data Acquisition Methods.
The ERBE scanner data are available from the Langley Distributed Active
Archive Center (DAAC) as well as the National Space Science Data Center
in Greenbelt, MD.
6.2 Spatial Characteristics.
ERBS scanner data coverage is from 70S to 70N latitude. The NOAA
satellites have complete global coverage. The original ERBE albedo data
had a spatial resolution of 2.5 x 2.5 degree latitude/longitude grid;
individual measurements have a resolution of about 40 km at nadir. For
this CD-ROM, the Goddard DAAC has mapped the data onto a 1 degree equal
angle lat/lon grid (see section 9.3.1 for details).
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 to these data.
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 |
--------------------------------------------------------------------------------
|ERBE_ALB | | | |
| |Clear sky albedo derived from ERBE |min = 0., |[unit- |ERBE |
| |data. Albedo is the fraction of |max = 1., |less]* | |
| |incident solar radiation that a |fill = -99.00 | | |
| |surface reflects. | | | |
| | | | | |
--------------------------------------------------------------------------------
*Albedo Units are non-dimensional, a 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.
ISCCP-C1 data.
9. DATA MANIPULATIONS
9.1 Formulas.
For details of the ERBE data processing algorithm, the user is referred
to Barkstrom and Smith (1986), Smith et al. (1986), Brooks et al. (1986),
Suttles et al. (1988, 1989), and the ERBE S4 User's Guide which is on-
line at the Langley DAAC. (userserv@eosdis.larc.nasa.gov)
9.1.1 Derivation Techniques/Algorithms.
Clear-sky albedo is calculated from ERBE measurements. For a
clear-sky shortwave measurement, the clear-sky albedo is defined
as the ratio of the outgoing shortwave to the incoming solar flux.
For that day, clear-sky albedos at other hours are filled in using
the ERBE directional models. Using only the days with clear-sky
measurements, the monthly average clear-sky albedo is determined.
The data are mapped onto a 1 x 1 degree grid for this data set.
9.2 Data Processing Sequence.
Top-of-atmosphere monthly mean albedo is derived from shortwave (0.2-5
m) radiances measured by the ERBE scanners (Kopia, 1986) on the ERBS and
NOAA-9 spacecraft.
9.2.1 Processing Steps and Data Sets.
See Barkstrom and Smith (1986) and Barkstrom et al. (1989).
9.2.2 Processing Changes.
This is the first version of this data set.
9.3 Calculations.
9.3.1 Special Corrections/Adjustments.
Below is a description of the re-gridding process done by the
Goddard DAAC:
Physical Lay Out of Original Data: These data were subset from
the GEDEX CD. Resulting Input data consisted of two files, with
each file containing one year worth of data. Within each file
the data were arranged with one data value and corresponding time,
latitude, and longitude per line.
Logical Lay Out of Original Data: These data were on a 2.5 x 2.5
degree grid, with the data starting at 0 longitude, 90 latitude
and progressing eastward, and then southward to 360 longitude, -90
latitude. The data at the poles consisted of only one grid value.
All other latitude bands consisted of a grid value every 2.5
degrees.
Processing Steps done by the Goddard DAAC: Regrid each
latitude and longitude band of data by implementing the
following steps:
1) Replicated every data value in each latitude band 360 times,
assigning them to a temporary array. Each of the original
latitude bands had 144 data values, which replicated 360
times produces a temporary array of 51840 data values for
that latitude band.
2) The first 144 (temporary array) data values are summed and
then divided by the number (144) of original latitude band
values. This was repeated 359 more times, for every 144
(temporary array) data values, in affect performing a linear
interpolation of the data within the latitude band.
3) Step 1 and 2 were repeated until all latitude bands have
been interpolated.
4) A test for fill value occurrence was performed. If fill
value constitutes 50 % or more of contributing values then
assign a fill value to that grid cell, otherwise compute the
average data value for grid cell from only those points
constituting data values. When assigning fill values, a new
fill value was used, as the existing one was extremely
large.
5) The same method, discussed above, was used for regridding
each longitude band of data, except that the number of
replications was 180. Utilizing the same test for fill
value mentioned above, and the same fill substitution.
6) The resulting array of data values were then split and
shifted from 0 longitude -> 360 longitude to -180 longitude
-> 180 longitude.
7) These data were then flipped from -180 longitude, -90
latitude to -180 longitude, 90 latitude.
9.4 Graphs and Plots.
Not available at this revision.
10. ERRORS
10.1 Sources of Error.
Errors in clear-sky albedo come from cloud contamination of the scene,
instrument errors, sampling errors, and uncertainties in models used in
processing.
10.2 Quality Assessment.
10.2.1 Data Validation by Source.
The ERBE clear-sky albedo values are validated by comparison
with data from other satellite and aircraft observations of
clear scenes.
10.2.2 Confidence Level/Accuracy Judgment.
The user is referred to Harrison et al. (1990) for a discussion
of ERBE error sources.
10.2.3 Measurement Error for Parameters and Variables.
Random error is about 0.01. Values may also be overestimated
slightly due to cloud contamination. (See Harrison et al.,
1990).
10.2.4 Additional Quality Assessment Applied.
Not available at this revision.
11. NOTES
11.1 Known Problems with the data.
There are no known data gaps or other problems.
11.2 Usage Guidance.
Errors in the polar regions may be larger than those quoted in Sec. 10
due to the inability to reliably distinguish between clouds and snow.
11.3 Other Relevant Information.
The clear sky albedos, estimated from ERBE, generally are a little
higher than albedos calculated for a molecular atmosphere with best
estimates of surface albedos (over the oceans surface albedos are low
and fairly well known). Some of this difference is likely due to
aerosols effect not included in the calculation and some due to the fact
that ERBE may designate scenes as clear when they have a small amount of
subpixel cloudiness in their view.
12. REFERENCES
12.1 Satellite/Instrument/Data Processing Documentation
Barkstrom, B. R., 1984. The Earth Radiation Budget Experiment (ERBE).
Bull. Amer. Meteorol. Soc., 65:1170-1185.
Barkstrom, B. R. and G. L. Smith, 1986. The Earth Radiation Budget
Experiment: Science and implementation. Rev. Geophys., 24:379-390.
Barkstrom, B. R., E. Harrison, G. Smith, R. Green, J. Kibler, R. Cess,
and the ERBE Science Team, 1989. Earth Radiation Budget Experiment
(ERBE) archival and April 1985 results. Bull. Amer. Meteorol. Soc.,
70:1254-1262.
Brooks, D. R., E. F. Harrison, P. Minnis, J. T. Suttles, and R. S.
Kandel, 1986. Development of algorithms for understanding the
temporal and spatial variability of the Earth's radiation balance.
Rev. Geophys., 24:422-438.
Harrison, E. F., P. Minnis, and G. G. Gibson, 1983. Orbital and cloud
cover sampling analyses for multisatellite Earth radiation budget
experiments. J. Spacecraft and Rockets, 20:491- 495.
Kopia, L. P., 1986. Earth Radiation Budget Experiment scanner
instrument. Rev. Geophys., 24:400-406.
Smith, G. L., R. N. Green, E. Raschke, L. M. Avis, J. T. Suttles, B. A.
Wielicki, and R. Davies. 1986. Inversion methods for satellite
studies of the Earth's radiation budget: Development of algorithms
for the ERBE mission. Rev. Geophys., 24:407-421.
Suttles, J. T., R. N. Green, P. Minnis, G. L. Smith, W. F. Staylor, B.
A. Wielicki, I. J. Walker, D. F. Young, V. R. Taylor, and L. L.
Stowe, 1988. Angular radiation models for Earth-atmosphere system,
vol. I, Shortwave radiation. NASA RP-1184.
Wielicki, B. A. and R. N. Green, 1989. Cloud identification for ERBE
radiative flux retrieval. J. Appl. Meteorol., 28:1133-1146.
12.2 Journal Articles and Study Reports
Barkstrom, B. R., E. F. Harrison, and R. B. Lee, 1990. Earth Radiation
Budget Experiment, Preliminary seasonal results. EOS Transactions,
American Geophysical Union, 71, February 27.
Harrison, E. F., Minnis, P., Barkstrom, B. R., and Gibson, G. G.:
Radiation Budget at the Top of the Atmosphere. Atlas of Satellite
Observations Related to Global Change, Edited by R. J. Gurney, J. L.
Foster, and C. L. Parkinson, Cambridge University Press, London,
1993.
Harrison, E. F., P. Minnis, B. R. Barkstrom, V. Ramanathan, R. D. Cess,
and G. G. Gibson, 1990a. Seasonal variation of cloud radiative
forcing derived from the Earth Radiation Budget Experiment. J.
Geophys. Res., 95:18687-18703.
Ramanathan, V., B. R. Barkstrom, and E. F. Harrison, 1989a. Climate and
the Earth's radiation budget. Physics Today, May, 22-32.
Ramanathan, V., R. D. Cess, E. F. Harrison, P. Minnis, B. R. Barkstrom,
E. Ahmad, and D. Hartmann, 1989b. Cloud-radiative forcing and
climate: Results from the Earth Radiation Budget Experiment.
Science, 243:57-63.
Zhang, M. H., R. D. Cess, T. Y. Kwon, and M. H. Chen, 1994. Approaches
of comparison for clear-sky radiative fluxes from general
circulation models with Earth Radiation Budget Experiment data. J.
Geophys. Res., 99:5515-5523.
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.
Not available at this revision.
14.2 Film Products.
Not available at this revision.
14.3 Other Products.
Not available at this revision.
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
ERBS Earth Radiation Budget Satellite
GSFC Goddard Space Flight Center
ISCCP International Satellite Cloud Climatology Project
ISLSCP International Satellite Land Surface Climatology Project
LaRC Langley Research Center
NASA National Aeronautics and Space Administration
NOAA National Oceanic and Atmospheric Administration