Note that some of the data files have been compressed using Zip compression. See Section 8.2 for details.
Smith, E. A., J. Lamm, and J. Gu. 2001. BOREAS Follow-On HMet-01 Merged SSM/I and Rain Gauge Precipitation Data. Data set. Available on-line [http://www.daac.ornl.gov] from Oak Ridge National Laboratory Distributed Active Archive Center, Oak Ridge, Tennessee, U.S.A.
1.2 Data Set Introduction
None given.
1.3 Objective/Purpose
The BOREAS rain gauge data that contributed
to the BOREAS Phase II Gridded Meteorological data is sparse, causing many
rain rate values to be interpolated. The Special Sensor Microwave/Imager
(SSM/I) data is also sparse. The data set provided here combines the BOREAS
Phase II Gridded Meteorological data and the hourly microwave rain rate
images from the SSM/I sensor into a gridded precipitation product with
fewer interpolated values.
1.4 Summary of Parameters
Precipitation in mm/hr.
1.5 Discussion
This data set combines a rain rate data
set based on 3 SSM/I satellites with a data set based on interpolated rain
gauge data. This combined SSM/I and rain gauge data set corresponds to
the 122 successive days starting on June 1, 1996 and ending on Sept. 30,
1996.
1.6 Related Data Sets
BOREAS Gridded Meteorological Data Over Hydromet Study Area 1994-1996
GPROF 4.0 6-Hourly Global Microwave Rain Rate Images
2.2 Title of Investigation
Retrieval of Surface Radiation Fluxes
Over BOREAS
2.3 Contact Information
Contact 1:
Professor Eric Smith
Florida State University
Tallahassee Fl
(850) 644-0922
(850) 644-9639 fax
email: esmith@metsat.met.fsu.edu
Contact 2:
Jim Lamm
Florida State University
Tallahassee Fl
(850) 644-8578
(850) 644-9639 fax
email: lamm@met.fsu.edu
Contact 3:
Jiujing Gu
Florida State University
Tallahassee Fl
(850) 644-7511
(850) 644-9639 fax
email: jgu@met.fsu.edu
4.1 Sensor/Instrument Description
None given.
4.1.1 Collection Environment
None given.4.1.2 Source/Platform
None given.4.1.3 Source/Platform Mission Objectives
None given.4.1.4 Key Variables
Precipitation.4.1.5 Principles of Operation
None given.4.1.6 Sensor/Instrument Measurement Geometry
None given.4.1.7 Manufacturer of Sensor/Instrument
None given.
4.2 Calibration
None given.
4.2.1 SpecificationsReturn to top of document.
None given.4.2.1.1 Tolerance
None given.
4.2.2 Frequency of Calibration
None given.4.2.3 Other Calibration Information
None given.
6.2 Field Notes
Not applicable.
7.1.1 Spatial CoverageCorner Latitude Longitude ------------------------------------------------------ NW 57° N 107° W NE 57° N 96° W SW 52° N 107° W SE 52° N 96° W7.1.2 Spatial Coverage Map
Not available.7.1.3 Spatial Resolution
The resolution of the data set is 10 minutes horizontal by 5 minutes vertical.7.1.4 Projection
The projection is latitude-longitude.7.1.5 Grid Description
The grid size is 66 columns by 60 lines.
7.2 Temporal Characteristics
7.2.1 Temporal Coverage
This combined SSM/I and rain gauge data set corresponds to the 122 successive days starting on June 1, 1996 and ending on Sept. 30, 1996.7.2.2 Temporal Coverage Map
Not applicable.7.2.3 Temporal Resolution
Data were gridded at an hourly interval. Temporal units are GMT.
7.3 Data Characteristics
7.3.1 Parameter/Variable
Precipitation.7.3.2 Variable Description/Definition
Precipitation amount, also referred to as rain rate.7.3.3 Unit of Measurement
mm/hour7.3.4 Data Source
Data sources are the hourly BOREAS Phase II Gridded Meteorological data and the 6-hourly microwave rain rate images from the SSM/I sensor.7.3.5 Data Range
None given.
7.4 Sample Data Record
Not applicable to binary gridded data.
96-mm-dd_hh_ssmi.zip
where 'mm' is the month, 'dd' is the day, and 'hh' is hours GMT for
the starting time of the corresponding one-hour interval.
Text file hmet01_ssmi_filecounts.dat
provides the number of pixels in each image that were derived based on
satellite versus rain gauge. See comments within that file for more info.
8.2 Data Format(s)
Files for the combined data set are
written out as 4 byte real numbers representing rain rates in mm/hr
(the data may need to be byte swapped to display correctly). The
format for this combined data set is exactly the same as the BOREAS Phase
II Gridded Meteorological data. For instance, they are both formatted as
binary files (see included FORTRAN program in section 14 for reading files).
The corresponding latitude and longitude for each pixel is the same as
that
for the BOREAS Phase II Gridded Meteorological data. The text file, hmet01_ssmi_lat_lon.dat
has also been provided, it lists the lat/long corresponding to each 4 byte
value as they appear consecutively in a file. Positive latitude values
are North, negative longitude values are West.
Each SSM/I file corresponds to one of
the following four six-hour time intervals:
9.1.1 Derivation Techniques and Algorithms
For the input data sets for this product:Rain gauge network
The data were interpolated using the weighted distance average of each pixel relative to each station. First, for each station the distance to the center of the pixel was determined, then the square of the inverse distances were added. For each station the square of the inverse distance to the pixel divided by the sum was used as a weight to obtain the interpolated value for the pixel.
This procedure did not produce satisfactory results for precipitation. In order to eliminate the large number of very low-intensity precipitation events caused by the interpolation of observed precipitation over large distances, a threshold method was applied for each grid. All time steps with a precipitation rate lower than the specified threshold were reset to zero and their precipitation amounts were added to the nearest event with a precipitation rate larger than the threshold. This method was found to yield the best results using a threshold precipitation rate of 0.075 mm/h. As a next step, the total number of rain-hours for each grid was calculated. For all grids there were approximately a total of 5000 rain-hour over the three years total (as opposed to the approximately 1500 rain-hours observed by the gauges). To solve this discrepancy, the length of all individual storms was rescaled by multiplying the length of the storm by the ratio of the number of observed to interpolated rain-hours. The new storm duration was centered around the midpoint of the original storm. For example, if an original storm lasted from 1000 through 1900 GMT (10 hours), and the length of the contracted storm was 5 hours, then the contracted storm would occur from 1200 through 1700 GMT. The total storm volume was conserved by first calculating the total volume of precipitation for both the original and contracted storms, and then by multiplying the precipitation rate of each time step of the contracted storm by the ratio of the original and contracted storm volumes. Using this method, we were able to conserve the diurnal cycle of precipitation and the total rainfall amounts, together with the storm duration and the distribution of rainfall rates (as observed by the various rain gauges).SSM/I precipitation
The Goddard Profiling Algorithm, Version 4 (GPROF4.0), is used to generate global rain rate maps every six hours centered on 00, 06, 12, and 18Z (i.e. 06Z is from 03 to 09Z). The global grid is 0.5 degrees latitude by 0.5 degrees longitude and extends from 90N to 90S and 0 to 360, resulting in an array size of 360 rows by 720 columns. The center of the grid box at position (1,1) is thus 89.75 N, 0.25 E.
Each time period produces two files; rain rate and observation population. The rain rate file contains floating-point values (R*4) in mm/hr. The observation file contains short-integer values (I*2) of the total pixels per grid box. Values in the observation files are negative when the corresponding rain rate is considered questionable. "Questionable" is defined as grid boxes that contain 10 percent or more "ambiguous" and "cold surface" pixels (as determined by the GPROF4 algorithm).
9.2 Data Processing Sequence
The only difference between the combined
data set presented here and the BOREAS Phase II Gridded Meteorological
Data is that many of the rain gauge values are replaced with rain rates
based on SSM/I measurements.
The method for making these replacements
is as follows.
9.2.1 Processing Steps
None given.9.2.2 Processing Changes
None given.
9.3 Calculations
None given.
9.3.1 Special Corrections/Adjustments
None given.9.3.2 Calculated Variables
None given.
9.4 Graphs and Plots
None.
10.2 Quality Assessment
None given.
10.2.1 Data Validation by SourceReturn to top of document.
None given.10.2.2 Confidence Level/Accuracy Judgment
None given.10.2.3 Measurement Error for Parameters
See Section 11.10.2.4 Additional Quality Assessments
None given.10.2.5 Data Verification by Data Center
None.
11.2 Known Problems with the Data
None given.
11.3 Usage Guidance
WARNING: This data set was completed
around May 13, 1999. Therefore, any changes made to the BOREAS Phase II
Gridded Meteorological data or the SSM/I data after this date have NOT
been taken into account.
11.4 Other Relevant Information
None given.
14.2 Software Access
NOTE: The file names for this data set
have been changed from "SSMIGauPrec_96_212_11.binC" to "96-07-30_11_ssmi_prec.bin"
to conform with the standard file naming scheme used in BOREAS. The following
program has *not* been rewritten to handle the new file names. You must
do that yourself (sorry).
FORTRAN Program For Reading In Data program readrr parameter (nx=66,ny=60) real rr(nx ,ny ) character fname*80,julian*3,ihr*2 call getarg(1,fname) open (1,file=fname,status='old',form='unformatted', & access='direct',recl=15840) read (1,rec=1) rr c123456789012345678901234567890 cSSMIGauPrec_96_212_11.binC read (fname,'(15x,a3,1x,a2)') julian,ihr rrm=0 do 20 j=1,ny do 10 i=1,nx rrm=rrm+rr(i,j) 10 continue 20 continue rrm=rrm/(nx*ny) write (*,'(a3,a2,f10.2)') julian,ihr,rrm stop endReturn to top of document.
ORNL DAAC User Services
Oak Ridge National Laboratory
(865) 241-3952
ornldaac@ornl.gov
ornl@eos.nasa.gov
15.2 Procedures for Obtaining Data
BOREAS data may be obtained through
the ORNL DAAC World Wide Web site at http://www.daac.ornl.gov/
[Internet
Link] or users may place requests for data by telephone
or by electronic
mail.
15.3 Output Products and Availability
Requested data can be provided electronically
on the ORNL DAAC's anonymous HTTP site or on various media including, CD-ROMs,
8-mm tapes, or diskettes.
16.2 Film Products
None.
16.3 Other Products
None.
17.2 Journal Articles and Study Reports
Pauwels, V.R.N., Examination of the Sources of Uncertainty in Land-Atmosphere
Model Results for Boreal Ecosystems, Ph.D. thesis, Department of Civil
Engineering and Operations Research, Princeton University, 1999.
Pauwels, V.R.N., J. Gu, B. Nijssen, A.K. Betts, K.R. Snelgrove, E.A. Whidden, N. Kouwen, D.P. Lettenmaier, E.A. Smith, E.D. Soulis, and E.F. Wood, A multiscale surface meteorological data set for BOREAS, in preparation.
GPROF 4.0 6-Hourly Global Microwave Rain Rate Images for 122 days in
1996 See ftp site: camille.gsfc.nasa.gov, pub/ssmi/BOREAS Contact Eric
Nelkin (nelkin@hilda.gsfc.nasa.gov) or George Huffman (huffman@agnes.gsfc.nasa.gov).
17.3 Archive/DBMS Usage Documentation
None.
ASCII - American Standard Code for Information Interchange BOREAS - BOReal Ecosystem-Atmosphere Study BORIS - BOREAS Information System CD-ROM - Compact Disk-Read-Only Memory DAAC - Distributed Active Archive Center DAT - Digital Archive Tape EOS - Earth Observing System EOSDIS - EOS Data and Information System FSU - Florida State University GMT - Greenwich Mean Time GSFC - Goddard Space Flight Center ISCCP - International Satellite Cloud Climatology Project NAD83 - North American Datum of 1983 NASA - National Aeronautics and Space Administration NOAA - National Oceanic and Atmospheric Administration NSA - Northern Study Area ORNL - Oak Ridge National Laboratory SSM/I - Special Sensor Microwave/Imager URL - Uniform Resource LocatorReturn to top of document.
Smith, E. A., J. Lamm, and J. Gu. 2001. BOREAS Follow-On HMet-01 Merged SSM/I and Rain Gauge Precipitation Data. Data set. Available on-line [http://www.daac.ornl.gov] from Oak Ridge National Laboratory Distributed Active Archive Center, Oak Ridge, Tennessee, U.S.A.
Keywords:
SSM/I
Rain Radar
Precipitation
Revision Date: Friday, 01-Nov-2024 13:12:35 EDT