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BOREAS FOLLOW-ON HMET-01 MERGED SSM/I AND RAIN GAUGE PRECIPITATION DATA
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Summary

A gridded data set has been assembled over the BOREAS hydro-meteorological study region that combines a precipitation data set based on a rain gauge network with precipitation estimates based on SSM/I satellite images. The result is an hourly precipitation data set covering 122 consecutive days beginning on June 1, 1996.

Note that some of the data files have been compressed using Zip compression. See Section 8.2 for details.

Data Citation

Cite this data set as follows (citation revised on October 30, 2002):

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.

Table of Contents

  1. Data Set Overview
  2. Investigator(s)
  3. Theory of Measurements
  4. Equipment
  5. Data Acquisition Methods
  6. Observations
  7. Data Description
  8. Data Organization
  9. Data Manipulations
  10. Errors
  11. Notes
  12. Application of the Data Set
  13. Future Modifications and Plans
  14. Software
  15. Data Access
  16. Output Products and Availability
  17. References
  18. Glossary of Terms
  19. List of Acronyms
  20. Document Information

1. Data Set Overview

1.1 Data Set Identification
      BOREAS Follow-On HMet-01 Merged SSM/I and Rain Gauge Precipitation Data

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

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2. Investigator(s)

2.1 Investigator(s) Name and Title
      Dr. Eric A. Smith, Professor

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

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3. Theory of Measurements

The only difference between the combined data set 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.
      For additional information on each input data set, see section 9.1.1 and appropriate references and documentation for those data.

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4. Equipment

For the equipment used in the collection of each of the data sources we refer to the documentation files of each data source individually.

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 Specifications
      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.

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5. Data Acquisition Methods

None given.

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6. Observations

6.1 Data Notes
      None given.

6.2 Field Notes
      Not applicable.

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7. Data Description

7.1 Spatial Characteristics
7.1.1 Spatial Coverage 
Corner              Latitude             Longitude 
------------------------------------------------------
NW                   57° N                 107° W
NE                   57° N                  96° W
SW                   52° N                 107° W
SE                   52° N                  96° W
7.1.2 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/hour

7.3.4 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.

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8. Data Organization

8.1 Data Granularity
      File names for the combined set are of the form:

      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:

  1. 2100 GMT of the previous day to 0200 GMT of present day
  2. 0300 GMT of the present day to 0800 GMT of present day
  3. 0900 GMT of the present day to 1400 GMT of present day
  4. 1500 GMT of the present day to 2000 GMT of present day
Thus, each SSM/I file corresponds to exactly six rain gauge based files that fall within its 6-hour time interval. An exception is the SSM/I file for time period 1 of day 1, since there is no rain gauge data for times 2100 GMT 2200 GMT and 2300 GMT of May 31. Also, rain gauge files for day 122 times 2100 GMT, 2200 GMT, and 2300 GMT have no corresponding SSM/I files and thus remain unchanged from BOREAS Phase II Gridded Meteorological data.
     The image files have been compressed with the MS Windows-standard Zip compression scheme. These files were compressed using Aladdin's DropZip on a Macintosh. DropZip uses the Lempel-Ziv algorithm (Welch, 1994), also used in Zip and PKZIP programs. The compressed files may be uncompressed using PKZIP (with the -expand option) on MS Windows and UNIX, or with StuffIt Expander on the Mac OS. You can get newer versions from the PKZIP Web site at http://www.pkware.com/download-software/ [Internet Link].

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9. Data Manipulations

9.1 Formulae
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.

  1. For every pixel in a given rain gauge file, acquire the SSM/I based rain rates for that pixel. Because there are three SSM/I satellites (F10, F11, F13) there can be as much as three of these SSM/I based rain rates. Also, because wide gaps exist between SSM/I swaths, there may be no SSM/I data for a given pixel.
  2. If no SSM/I measurements exist, retain the rain gauge measurement. Otherwise, average the one or more SSM/I based measurements and use this as the new rain rate value for that pixel.
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.

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10. Errors

10.1 Sources of Error
      This data set was completed around May 13, 1999. Therefore, changes made to the BOREAS Phase II Gridded Meteorological data in August 1999 or any changes to the SSM/I data after this date have NOT been taken into account.

10.2 Quality Assessment
      None given.

10.2.1 Data Validation by Source
      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.

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11. Notes

11.1 Limitations of the Data
      None given.

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.

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12. Application of the Data Set

These data were derived for temporal and spatial modeling at regional scales.

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13. Future Modifications and Plans

None.

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14. Software

14.1 Software Description
      Software code that can be used to read the data is provided below.

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

    end
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15. Data Access

15.1 Contact for Data Center/Data Access Information
      These BOREAS data are available from the Earth Observing System Data and Information System (EOS-DIS) Oak Ridge National Laboratory (ORNL) Distributed Active Archive Center (DAAC). The BOREAS contact at ORNL is:

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.

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16. Output Products and Availability

16.1 Tape Products
      None

16.2 Film Products
      None.

16.3 Other Products
      None.

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17. References

17.1 Platform/Sensor/Instrument/Data Processing Documentation
      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.

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18. Glossary of Terms

None given.

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19. List of Acronyms

    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 Locator
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20. Document Information

20.1 Document Revision Dates

Written: 21-Jul-2000
Last Updated: 05-Feb-2001 (citation revised on 30-Oct-2002)

20.2 Document Review Dates

BORIS Review:
Science Review:

20.3 Document ID

hmet01_ssmi_precip

20.4 Citation

Cite this data set as follows (citation revised on October 30, 2002):

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.

20.5 Document Curator:

webmaster@daac.ornl.gov

20.6 Document URL:

http://daac.ornl.gov/BOREAS/FollowOn/guides/hmet01_ssmi_precip_doc.html

Keywords:
SSM/I
Rain Radar
Precipitation

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Revision Date: Monday, 22-Apr-2024 10:02:01 EDT