Welcome to the
NOAA/NASA Pathfinder Climate Data CD-ROM

This CD-ROM contains seven data sets from the NOAA/NASA Pathfinder Program. The majority of the data are monthly one- by one-degree gridded files with many parameters, most of which are climate-related and can be used for analysis and research. The data are for the Pathfinder Benchmark period: April, 1987, through December, 1988.

The data sets included on this CD are:

Advanced Very High Resolution Radiometers (AVHRR) Land, and

Advanced Very High Resolution Radiometers (AVHRR) Ocean,

TIROS Operational Vertical Sounder (TOVS) Path - A,

TIROS Operational Vertical Sounder (TOVS) Path - C1, and

TIROS Operational Vertical Sounder (TOVS) Path - C2,

Special Sensor Microwave/Imager (SSM/I) Precipitation, and

Special Sensor Microwave/Imager (SSM/I) Atmospheric Moisture.

Important information on the CD-ROM directory structure, instructions on visualization and browse software, an overview of the data and list of some NOAA/NASA Pathfinder web sites are all available in this document.

Directory Structure

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The highest level of the directory structure has directories for each of the data sets and for software. The software directory includes tools developed at NOAA's National Geophysical Data Center (NGDC) for viewing the data as well as the files required to install the runtime version of Microsoft Video for Windows for viewing the movies included on the disc.

Many levels of the structure include directories named doc, data, movies, or process. The doc directories contain the documentation from the data provider for that data set. The data directories contain simple binary files of gridded data (.img) described in the ASCII documentation files (.doc), and external Hierarchical Data Format header files (.hdf). Some data directories include a directory named imdi_lbl. These directories contain external header files (.lbl) for the NASA Planetary Data System (PDS) DOS display program IMDISP for viewing integer data grids. The movie directories contain animation's of each parameter (.AVI). These animation's can be viewed using the Windows Media Player if Video for Windows has been installed. The process directories include data set dependent software tools that we have developed and used to process the data sets.

File Name Extensions

Extension	Description of Extension
.doc	ASCII documentation files
.img	Simple binary files of gridded data
.lst	GeoVu histogram information (variable summary) file
.hdf	Hierarchical Data Format (HDF) files
.fmt	Format descriptions define the formats of input and output data and headers.
.avi	Movie files for each parameter
.men	GeoVu uses custom menu files for each data collection that enables the end use to easily navigate the data.
.lbl	External header files for the NASA Planetary Data System (PDS) DOS display program IMDISP for viewing integer data grids.

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Viewing the Data

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The goal of this project is to make data easy to view with a wide variety of tools. The .img files on this disk are simple binary images (rows and columns:(90,180), (180,360) and (360,720), pc byte order). These can be viewed with many image visualization tools.

GEOVU - GeoVu is included to provide all users with basic access to the data. It is not intended to replace more sophisticated tools. This CD includes GeoVu for the PC, Mac, Sun and SGI (Silicon Graphics Workstations running UNIX). At NGDC, we have an online GeoVu FAQ which attempts to answer commonly asked questions about GeoVu. Please note that the PC GeoVu (Release 6.X) supports the movie browser however the Mac, SGI and UNIX version of GeoVu do not have a movie browser. To view the movies on the Mac or a UNIX machine see the movies section below.

To install GeoVu follow the instructions in the following files:

PC	/software/geovu/pc/read_pc.htm	(Disk space needed to install GeoVu on the PC is ~4.6 mb)
Mac	/software/geovu/mac/read_mac.htm	(Disk space needed to install GeoVu on the Mac is ~5.1 mb)
Sun	/software/geovu/unix_sun/read_sun.htm	(Disk space needed to install GeoVu on the Sun is ~7.6 mb)
SGI	/software/geovu/unix_sgi/read_sgi.htm	(Disk space needed to install GeoVu on the SGI is ~5.3 mb)

HDF -There are 2 types of Hierarchical Data Format (HDF) files on this CD-ROM. The original HDF files provided to NGDC by the data contributors and the external HDF header files created by NGDC. NGDC created the external HDF header files to expand access to the image (.img) data. The original HDF files are written in big endian byte order. They are platform independent and can be viewed using any HDF tool. Due to space limitations on this CD-ROM, the original HDF files are provided for only some of the datasets. The original HDF files are located in the org_hdf directory under the appropriate data directory. For example, the AVHRR Land original HDF files are in the directory /avhrr_ld/data/org_hdf. The Tovs Path - C2 original HDF files are in the directory /tovs_c2/apr87/org_hdf. The following datasets have the original HDF files:

AVHRR Land

TOVS Path - C1

TOVS Path - C2

SSM/I Precipitation

SSM/I Atmospheric Moisture

EXTERNAL HDF FILES - The external HDF header files, created at NGDC, describe simple binary gridded data files (.img files). The external HDF header contains a data description that enables an HDF viewer, able to read external headers, to display the selected .img data file. The external HDF header files (.hdf) are in the data directories with all the ".img", and ".doc" files.

At the present there is only one viewer that can handle the external HDF files, Noesys from Fortner Research Version 1.02. JHV Version 1.20 beta from the National Center for Supercomputing Applications (NCSA) has a problem reading the external HDF files due to the files being in pc byte order (little_endian). JHV doesn't presently support swapping bytes when external file elements are involved. This situation is being addressed by NCSA and should be rectified in there next release of JHV due out at the end of February, 1998.

LISTS (*.lst): In the lists directory (under the data directory) are ASCII x-y files that give the distribution of each parameter for that month and checkvar.out which lists the minimum and maximum for each parameter/month.

EXTERNAL .LBL FILES - The SSM/I Precipitation and Atmospheric Moisture and TOVS Path A and C1 data areas contain sub-directories named imdi_lbl. These directories contain external header files (.lbl) for the NASA PDS DOS display program, IMDISP, for viewing integer data grids. IMDISP only supports the following data types: byte, integer and long integer. For the Pathfinder data sets, if the data type is byte or short, then the image file has an external label file (.lbl). If the data type is float, then there is no external label file.

There seems to be a problem with IMDISP handling the signed short data types. If the keyword "UNSIGNED_INTEGER" is used in the label file to describe data that is actually signed integers, the image is displayed properly. However, there seems to be a glitch in the in the x-axis plotting for histograms. The histograms are labeled 0 to -32768 rather than -10 to 10000. In the PDS documentation it states that for signed integers use the following keywords: PC_INTEGER or LSB_INTEGER. If either of these 2 keywords are used for the data type descriptor, then the images come out very dark. The keyword "PC_INTEGER" was used for the Pathfinder data, even though this causes dark displays. The data sets affected by this are:

1. Tovs A - 273 files - all Count image files (21 x 13 = 273)
2. SSM/I Precipitation - 14 files - Counts only (14 x 1 = 14)
3. SSM/I Atmospheric Moisture - 28 files - Counts only (14 x 2 =28).

MOVIES - The movies, written as Video for Windows files (".avi"), can be viewed using the Windows Media Player from your PC's Accessories Group. The PC version of GeoVu is the only platform with a built in movie browser. All the Video for Windows movie files have an ".avi" extension. All the ".mov" files in the movies directory are the header files for the GeoVu PC built in movie browser. (They are not in the Quicktime .mov format).

For the MAC user, you can download and use the free utility avi_to_qt.kit located at http://www.esperance.com/hacks to convert the .avi files to the Quicktime movie format.

For the UNIX user, you can download and use the free utility Xanim located at http://xanim.va.pubnix.com to view or convert the .avi files.

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Pathfinder Data Set Overview

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AVHRR - Land

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This CD-ROM contains data produced by the AVHRR Land group and provided to NGDC by Mary James of NASA Goddard Space Flight Center (Replaced by Peter Smith 301-763-8071 of NASA Goddard Space Flight Center).

Goddard Space Flight Center
Code 902.2
Greenbelt, Maryland 20771
Telephone: (301) 286-5033
Fax: (301) 286-1775
email: gsfc@eos.nasa.gov

This data set is part of the Advanced Very High Resolution Radiometer (AVHRR) Pathfinder Land Products. It consists of normalized difference vegetation index in 1 degree latitude - longitude equal angle bins. It is derived from the mean Channel 1 and mean Channel 2 reflectance for 1 degree areas for the Pathfinder Land 10-day Composite Data set. The periods are the 1st through the 10th, 11th through the 20th and 21st through the end of the month.

The only parameter for this data set is:

• Normalized Difference Vegetation Index (NDVI).

The data has been descaled for the physical NDVI values which range from -1.0 to 1.0. The equation to do the computation is:

The original HDF data files denoted missing data and ocean data with values of 0 and 1 respectively. We remapped the 0 and 1 flags to 2 and 3 respectively to move the missing data flags out the the valid data range. The descaled data now have a valid data renge fo -0.5 to 0.77 with flag values of 2.0 for missing data and 3.0 for ocean data.

For this dataset, the overall minimum is -0.5 and the maximum is 3.0. If we use these minimum and maximum, GeoVu displays the images as black due to compressing the data into a small part of the pallette. To create a meaningful display in GeoVu, the minimum and maximum values for the entire data set have been set to -0.5 and 0.77. This results in a meaningful display with the missing data flags being consistently displayed with the same color.

AVHRR Land Table

For the data providers documentation on this dataset.

AVHRR Land web site.

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AVHRR - Ocean

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This CD-ROM contains data produced by the AVHRR Ocean group and provided to NGDC by Dr. Jorge Vazquez (818-354-6980) from the Jet Propulsion Laboratory .

Jet Propulsion Laboratory
4800 Oak Grove Drive
Mail Stop 300-320
Pasadena, California 91109
Telephone: (818) 354-9890
Fax: (818) 393-2718
email: jpl@eos.nasa.gov

The NOAA/NASA Pathfinder AVHRR Oceans data sets are global, multichannel, Sea Surface Temperature data derived from the Advanced Very High Resolution Radiometers (AVHRR) on the NOAA/TIROS operational meteorological satellites (NOAA-7, -9, and -11). These satellites provide a continuous daily and composite data set. This data collection includes monthly global browse images of the Sea Surface Temperature in half degree latitude-longitude equal angle bins. The product choosen for this cdrom is the Best Sea Surface Temperature Equal Area Browse HDF files (720x360). These images were created by binning the AVHRR level-1B data. The data provided is January to December for 1987.

Rescaling of the SST values

NGDC received the original source files as bytes. The data was descaled into floats by NGDC to regain the original data value in degree celsius. The equation to calculate the original SST is:

  SST = 0.15*DN + (-3.0)
	where:
        SST = sea surface temperature (degrees Celsius)
	DN = digital number
        (DN = 0) Indicates a missing value or the presence of ice, land or cloud coverage.

This data set only has one parameter:

• Sea Surface Temperature (SST)

The flag value for the Sea Surface Temperature is -3 which indicates a missing value or the presence of ice, land or cloud coverage.

AVHRR Ocean Table

For the data providers data description on this dataset.

For the data providers user guide on this dataset.

AVHRR Ocean web site.

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TOVS PATH - A

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This CD-ROM contains data produced by the TOVS Path A group and provided to NGDC by Geoge Serafino (301-286-3021) of NASA Goddard Space Flight Center.

Goddard Space Flight Center
Code 902.2
Greenbelt, Maryland 20771
Telephone: (301) 286-5033
Fax: (301) 286-1775
email: gsfc@eos.nasa.gov

Due to the experimental nature of this CD-ROM and the space limitations only the AM data were processed. This dataset contains the TIROS Operational Vertical Sounder (TOVS) level 3 geophysical parameters. For each parameter, each cell in a 1 by 1 degree grid is characterized by a mean value, a standard deviation, and the number of observations. There are grids for each month. This data collection includes the following parameters:

• Coarse layer mean temperature for the surface-500, 500-300, 300-100, and 100-30 mb layers.
• Total cloud fraction.
• Outgoing longwave radiation.
• Cloud top pressure.
• Total precipitable water value above surface, 850, 700, 500, and 300 mb

Missing Data Values

For all mean and standard deviation arrays, a fill of -999.99 is used to indicate that data for that gridbox is either missing, invalid or suspect. For the count arrays, a corresponding fill value of 0 is used under these circumstances.

Tovs Path A Table

For the data providers documentation on this dataset.

For the data providers readme on this dataset.

Tovs Path A web site.

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TOVS PATH - C1

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This CD-ROM contains data produced by the TOVS Pathfinder group and provided to NGDC by Janice Tillman (205-922-5875) and Michael Goodman (205-922-5890) both from the NASA Marshall Space Flight Center.

Marshall Space Flight Center
Building 4492
Huntsville, Alabama 35812
Telephone: (205) 544-6329
Fax: (205) 544-5147
Email: msfc@eos.nasa.gov

Due to the experimental nature of this CD-ROM and the space limitations only the AM data was processed. This data collection includes global 1 X 1 images for 3 parameters:

• Lower Stratosphere Temperature
• Lower Tropospheric Temperature
• Ocean Precipitation

The temperature images were created by binning the Level 2 TOVS data. Three images exist for each parameter:

1. the mean for each pixel
   
2. the standard deviation
   
3. the count.
   

The ocean precipitation images were created differently. Note that the ocean precipitation data sets are identical for the AM and PM satellites. Only the ocean precipitation AM directories were processed.

Missing Data Values

Oceanic precipitation estimates are only calculated between the latitudes 60S and 60N. All grids outside this latitude band are set to -999.00. All variables for TOVS C1 have a missing data flag value of -999.00.

Variable                           Missing flag value

Lower Tropospheric Temperature        -999.00
Lower Stratospheric Temperature       -999.00
Standard Deviation Troposphere        -999.00
Standard Deviation Stratosphere       -999.00
Counts Troposphere                    -999.00
Counts Stratosphere                   -999.00
Ocean Precipitation                   -999.00

Potential Data Errors

The Ocean Precipitation data presents many interesting challenges. The missing data flag of -999 creates problems for display programs which insist on calculating the minimum and the maximum from all of the data. Also, while most data values are between 0 and 20, there are a number of data values which are above 100. These seem to occur in the Hudson Bay and Sea of Japan. The spatial concentration of these data suggest that these may be bad data values. This data range problem causes a very dark image for the individual data and movie files for the ocean precipitation variable.

Tovs Path C1 Table

Name	Filename	Type	Min	Max	Units	Comments
Lower Tropospheric Temperature Lower Stratospheric Temperature Standard Deviation Troposphere Standard Deviation Stratosphere Counts Troposphere Counts Stratosphere Ocean Precipitation	lstrtemp ltrotemp ltrostd lstrstd ltrocnt lstrcnt ocnprecp	Mean Mean Std Dev Std Dev Count Count Mean	184.00 195.00 0.00 0.00 0.00 0.00 0.00	238.00 287.00 7.50 2.30 155.00 157.00 121.50	K K K K Number Number mm/day	Flag value = -999.00

For the data providers documentation on this dataset.

Tovs Path C1 web site.

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TOVS PATH - C2

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This CD-ROM contains data produced by the NOAA TOVS Pathfinder group and provided to NGDC by Mitch Goldberg (301-763-8136). The data are available at the Satellite Active Archive.

Satellite Active Archive
5627 Allentown Road
Suite 100 PES
Suitland, Maryland 20746
Telephone: (301) 763-8400
Fax: (301) 763-8443
email: saainfo@nesdis.noaa.gov

This data collection includes global 2 X 2 images for 11 parameters:

• MSU Adjacent FOV Deep Layer Temp. (650mb)
• Scan Line Deep Layer Temp. (100, 150, 225, 350, 500, and 800 mb)
• Limb Corrected Brightness Temp. (Surface, 90, 300, and 600 mb)

These images were created by binning the Level 2 TOVS data. Three images exist for each parameter:

1. the mean for each pixel
2. the standard deviation
3. the count.

The NOAA TOVS Pathfinder Group converted floating point values into integers by applying a scaling or unit conversion to allow for a smaller transfer file size. The data providers multiplied standard deviation data values by 256 and multiplied the mean data values by 64. At NGDC, we applied the reverse conversion to recover the original units. Standard deviation data were divided by 256 and the mean data were divided by 64. We provide this data set in both converted (image) and original units (scatter plot).

The original transfer files contained 11 parameters (e.g., scan line deep layer temperature at the 100 millibar level) and each parameter contains three statistics (i.e., count, mean, and standard deviation). We divided each parameter and statistic into separate files and applied unit conversions to recover the original floating point values. The transfer (original units) files are displayed in GeoVu as point displays (scatter plots) and the converted files as image displays.

Original data file: (Point data on the CD-ROM)

• The data providers multiplied Standard deviation data by 256
• The data providers multiplied mean data by 64
  

Processed Data file: (Image data on the CD-ROM)

• Standard deviation data has been divided by 256
• Mean data has been divided by 64.
  

The missing data flag value for this data set is 0. The counts have a value of 0 for the first few rows at the top and bottom of each data file.

Potential Data Errors

In processing the TOVS Path C2 data we discovered several pixels that appear to be inconsistent. These are:
October 1987 MSU Channel 2 Standard deviation image has a value of 5988 at point 176,0.
October 1987 MSU Channel 3 Standard deviation image has a value of 2381 at point 176,0.

Tovs Path C2 Table

Name	Filename	Point Data Histogram Filename	Description	Type	Min	Max	Units
SDLCT SDLMT LCBT SDLST	CNT_100 CNT_150 CNT_225 CNT_350 CNT_500 CNT_650 CNT_800 MEAN_100 MEAN_150 MEAN_225 MEAN_350 MEAN_500 MEAN_650 MEAN_800 MSU1_CT MSU1_MN MSU1_SD MSU2_CT MSU2_MN MSU2_SD MSU3_CT MSU3_MN MSU3_SD MSU4_CT MSU4_MN MSU4_SD STD_100 STD_150 STD_225 STD_350 STD_500 STD_650 STD_800	dlt1_count dlt2_count dlt3_count dlt4_count dlt5_count FOV_count dlt6_count dlt1_mean (x64*) dlt2_mean (x64*) dlt3_mean (x64*) dlt4_mean (x64*) dlt5_mean (x64*) FOV_mean (x64*) dlt6_mean (x64*) lcbt1_count lcbt1_mean (x64*) lcbt1_std (x256**) lcbt2_count lcbt2_mean (x64*) lcbt2_std (x256**) lcbt3_count lcbt3_mean (x64*) lcbt3_std (x256**) lcbt4_count lcbt4_mean (x64*) lcbt4_std (x256**) dlt1_sd (x256**) dlt2_sd (x256**) dlt3_sd (x256**) dlt4_sd (x256**) dlt5_sd (x256**) FOV_std (x256**) dlt6_sd (x256**)	Scan Line Deep Layer Temperature(100 mb) Scan Line Deep Layer Temperature(150 mb) Scan Line Deep Layer Temperature(225 mb) Scan Line Deep Layer Temperature(350 mb) Scan Line Deep Layer Temperature(500 mb) MSU Adjacent FOV Deep Layer Temp (650 mb) Scan Line Deep Layer Temperature(800 mb) Scan Line Deep Layer Temperature(100 mb) Scan Line Deep Layer Temperature(150 mb) Scan Line Deep Layer Temperature(225 mb) Scan Line Deep Layer Temperature(350 mb) Scan Line Deep Layer Temperature(500 mb) MSU Adjacent FOV Deep Layer Temp (650 mb) Scan Line Deep Layer (800 mb) Limb Corrected Brightness temp (Surface) Limb Corrected Brightness temp (Surface) Limb Corrected Brightness temp (Surface) Limb Corrected Brightness temp (600 mb) Limb Corrected Brightness temp (600 mb) Limb Corrected Brightness temp (600 mb) Limb Corrected Brightness temp (300 mb) Limb Corrected Brightness temp (300 mb) Limb Corrected Brightness temp (300 mb) Limb Corrected Brightness temp (90 mb) Limb Corrected Brightness temp (90 mb) Limb Corrected Brightness temp (90 mb) Scan Line Deep Layer Temperature(100 mb) Scan Line Deep Layer Temperature(150 mb) Scan Line Deep Layer Temperature(225 mb) Scan Line Deep Layer Temperature(350 mb) Scan Line Deep Layer Temperature(500 mb) MSU Adjacent FOV Deep Layer Temp (650 mb) Scan Line Deep Layer Temperature(800 mb)	Count Count Count Count Count Count Count Mean Mean Mean Mean Mean Mean Mean Count Mean Std Dev Count Mean Std Dev Count Mean Std Dev Count Mean Std Dev Std Dev Std Dev Std Dev Std Dev Std Dev Std Dev Std Dev	0 0 0 0 0 0 0 179.813 192.906 203.781 203.406 211.000 199.641 170.219 0 158.094 0.0039 0 200.328 0.0039 0 197.422 0.0039 0 182.234 0.0039 0.0156 0.0039 0.01170 0.01950 0.03120 0.0039 0.0078	87 87 87 87 87 130 87 239.813 231.000 240.797 258.781 267.453 278.828 294.844 120 291.922 27.6719 120 265.609 11.2305 120 235.875 11.2539 120 242.734 21.8867 16.4531 13.0625 8.97266 8.37891 8.78125 19.6641 30.0742	Number Number Number Number Number Number Number K K K K K K K Number K K Number K K Number K K Number K K K K K K K K K

*multiply data values by 64
**multiply data values by 256

For the data providers documentation on this dataset.

Tovs Path C2 web site.

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SSM/I PRECIPITATION

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This CD-ROM contains data produced by the SSM/I group and provided to NGDC by Ron Schudalla (205-922-5792) of Marshall Space Flight Center (MSFC).

Marshall Space Flight Center
Building 4492
Huntsville, Alabama 35812
Telephone: (205) 544-6329
Fax: (205) 544-5147
Email: msfc@eos.nasa.gov

This data collection includes global 1 X 1 grids characterized by a weighted average value, a sum of the squared precipitation rates and the number of pixels per bin. The 3 parameters are:

• Precipitation Rate Grid (PRG)
• Sum of the Squared Precipitation Rates (SSQ)
• Number of Pixels per Bin (NUM)

The Sum of the Squared Precipitation Rates (SSQ) was not processed due to an error in the processing prior to our receiving the data. The sums were calculated as floating point values and then converted to 4 byte integers. Sums which were larger than the maximum value of a 4 byte integer were truncated in this process. The effect of this truncation is that the maximum value for the SSQ variable is 2,147,483,647 which is incorrect. Many months of data include over 300 of these values. There is no way to correct this error without reprocessing the original data. The SSQ images are on the CD-ROM as floats, but are not accessible from the GeoVu menu files. Also, no movie has been made for the SSQ parameter.

The satellite was launched in July, 1987, so the SSM/I Benchmark period is from August 1987 to November 1988. As opposed to the usual starting period of April 1987. The December 1987 monthly file was not generated because the SSM/I instrument was turned off on December 3, 1987 due to overheating. The January 1988 monthly file was also not generated.

Missing Data Values

                  Flags For Precipitation Rates

                 -------------------------------
                 |           | FLAG 1 | FLAG 2 |
                 -------------------------------
                 |PRG, SSQ   | -10   |  -20    |
                 -------------------------------

where:
PRG = Monthly Precipitation Rate
SSQ = Monthly Precipitation Rate Squared
FLAG 1 = No precipitation rate data was accumulated in the bin.
FLAG 2 = For pentads, if more than 40% of the valid pixel precipitation values in a bin were associated with the cold surfaces and/or identified as ambiguous, the bin value is set to the -20. For monthly grids, a 20% threshold is used.

Rescaling of the Pentad (Monthly)Precipitation Rate Grid (PRG)

The original monthly precipitation rate grid values are a weighted average of valid precipitation rate values multiplied by 100 before storing to retain a precision of 0.01 mm/day. For example, 31.5 mm/day is stored as 3150. At NGDC, we descaled the PRG data by dividing each data value by 100 except the two flag value of -10 and -20.

Original data file:

• The data providers multiplied Precipitation Rate Grid (PRG) data by 100

Processed Data file: (Image data on the CD-ROM)

• Precipitation Rate Grid (PRG) data has been divided by 100

SSM/I Precipitation Table

Name	Filename	Description	Type	Min	Max	Units	COMMENTS
PRG	MMMYYPRG	Precipitation Rate Grid	Weighted average	-20	77.93	mm/day	MMM= month,YY = year Flag values = -10, -20.
SSQ	Not processed	(See above)
NUM	MMMYYNUM	Number of Pixels per Bin	Count	-20	4442	Number	Flag values = -10, -20.

For the data providers documentation on this dataset.

SSM/I Data web site.

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SSM/I ATMOSPHERIC MOISTURE

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This CD-ROM contains data produced by the SSM/I group and provided to NGDC by Ron Schudalla (205-922-5792) of Marshall Space Flight Center (MSFC).

Marshall Space Flight Center
Building 4492
Huntsville, Alabama 35812
Telephone: (205) 544-6329
Fax: (205) 544-5147
Email: msfc@eos.nasa.gov

This data collection includes global 1X1 grids characterized by a weighted average value, a sum of the squared precipitation rates and the number of pixels per bin. The 6 parameters are:

• Cloud/Rain Liquid Water (LWG)
• Sum of Squared Cloud/Rain Liquid Water values (LWS)
• Number of Cloud/Rain Liquid Water Pixels per Bin (LWN)
• Columnar Water Vapor (WVG)
• Sum of Squared Columnar Water Vapor Values (WVS)
• Number of Columnar Water Vapor Pixels per Bin (WVN)

The Sum of the Squared Cloud/Rain Liquid Water values (LWS) contains the same error as described above for the SSM/I Precipitation data set. There is no way to correct this error without reprocessing the original data. Unlike the SSM/I data, NGDC processed the LWS data with the error because there were only 10 pixels with the maximum value of 2,147,483,647. The LWS data for March 1988 and April 1988 were changed from 2,147,483,647 to 2,147,483,520 to make processing possible. March 1988 data at the following 6 x, y locations were changed; x, y pairs: (32,325), (31,326), (32,326), (31,327), (32,327), and (31,328). April 1988 data at the following 4 x, y location were changed; x, y pairs: (31,325), (32,325), (33,325) and (32,326).

The original March 1988 image is saved as mar88lws.old in the directory \ssmi_at\mar88\org_hdf\. The original April 1988 image is saved as apr88lws.old in the directory \ssmi_at\apr88\org_hdf\. The corrected image files, mar88lws.img and apr88lws.img are used in all of our subsequent processing.

The palette file rainbow.pal was used for the parameters Cloud/Rain Liquid Water (LWG) and Sum of Squared Cloud/Rain Liquid Water values (LWS). These two parameters have a nonlinear distribution of the data values. A majority of the data values are clustered around zero, but also have high maximums. Viewing the data with the standard Pathfinder palette file RGB_256.pal results in a black image. To get a meaningful display of the image, the 16 color palette rainbow.pal was used and the number of display colors was set to 256. By doing this, the colors of rainbow.pal correspond to the first 16 data bins, where 95% of the data values fall. All the other parameters for the SSM/I Atmospheric Moisture data used the RGB_256.pal for the palette file. One can still select the palette file RGB_256.pal in GeoVu by choosing "search" and "create" and then select RGB_256.pal. In the movie files for the parameters LWG and LWS the palette RGB_256.pal was used. This creates very dark movies due to the nonlinear distribution of the data values.

The satellite was launched in July 1987, so the SSM/I Benchmark period extends from August 1987 to November 1988 as opposed to the usual start of April 1987. The December 1987 monthly file was not generated because the SSM/I instrument was turned off on December 3, 1987 due to overheating. The January 1988 monthly file was also not generated.

Missing Data Values

                Flags For Atmospheric moistures

                 -------------------------

                 |            | FLAG 1   |
                 -------------------------
                 | LWG      |      -10   |

                 | WVG      |      -10   |

                 -------------------------

where:
LWG = Monthly Cloud/Rain Liquid Water in mg/cm2
WVG = Monthly Columnar Water Vapor in g/cm2
FLAG 1 = No atmospheric moisture data was accumulated in the bin.

Rescaling of the Cloud/rain liquid water (LWG) and Columnar Water Vapor Grid (WVG)

The original monthly Cloud/rain liquid water grid values were multiplied by 10 before storing to retain a precision of 0.1 mg/cm2. For example, 31.5 mm/day is stored as 315. At NGDC, we descaled the LWG data by dividing each data value by 10 except the flag value of -10. The minumum value is 0, and the maximum unscaled value is 1000.

The origianl monthly Columnar Water Vapor Grid (WVG) values were multiplied by 100 before storing to retain a precision of 0.01 g/cm2. For example, 3.15 g/cm2 is stored as 315.At NGDC, we descaled the WVG data by dividing each data value by 100 except the flag value of -10. The minumum value is 0, and the maximum unscaled value is 10.

Original data file:

• The data providers multiplied Cloud/rain liquid water (LWG) data by 10
• The data providers multiplied Columnar Water Vapor Grid (WVG) data by 100

Processed Data file: (Image data on the CD-ROM)

• Cloud/rain liquid water (LWG) data has been divided by 10
• Columnar Water Vapor Grid (WVG) data has been divided by 100

SSM/I Atmospheric Moisture Table

Name	Filename	Description	Type	Min	Max	Units	COMMENTS
LWG	MMMYYlwg	Cloud/Rain Liquid Water	Weighted average	-10	1000	mg/cm2	MMM= month,YY = year
LWS	MMMYYlws	Sum of Squared Cloud/Rain Liquid Water values	sum of the squares	-10	2147383250	mg2/cm4	2147383250 is the corrected max value for the lws parameter
LWN	MMMYYlwn	Number of Cloud/Rain Liquid Water Pixels per Bin	Count	-10	1110	number
WVG	MMMYYwvg	Columnar Water Vapor	Weighted average	-10	10	g/cm2
WVS	MMMYYwvs	Sum of Squared Columnar Water Vapor Values	sum of the squares	-10	6273969	g2/cm4	Flag values = -10 for all parameters.
WVN	MMMYYwvn	Number of Columnar Water Vapor Pixels per Bin	Count	-10	1110	number

For the data providers documentation on this dataset.

SSM/I Data web site.

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