ISCCP/Ice Snow indexed Documentation


Content


1.TYPE OF DATA

2.SPATIAL CHARACTERISTICS

3.TEMPORAL CHARACTERISTICS

4. INSTRUMENT DESCRIPTION

5. DATA PROCESSING SEQUENCE

6. QUALITY ASSESSMENT

7. CONTACTS FOR DATA PRODUCTION INFORMATION

8. OUTPUT PRODUCTS AND AVAILABILITY

9. DATA ACCESS

10. CONTACTS FOR ARCHIVE/DATA ACCESS INFORMATION

11. REFERENCES

12. RELATED DATA SETS

13. SUMMARY/SAMPLE

14. NOTES



1. TYPE OF DATA

1.1 Parameter/Measurement.

Sea ice fraction and snow cover.

1.2 Unit of Measurement.

Sea ice fraction in tenths and snow/no snow information (snow=1 and no snow=0).

1.3 Data Source.

The International Satellite Cloud Climatology Project (ISCCP) ice/snow data set was created by combining two Navy/National Oceanic and Atmospheric Administration (NOAA) data sets: sea ice and snow data. The sea ice data were derived from the weekly analyses of ice maps prepared by the Navy/NOAA Joint Ice Center. The weekly analyses are based on four types of data: shore station reports, ship reports, aerial reconnaissance and satellite image analysis. The satellite-based information constitutes 90-98% of the total and comes from two types of data: visible/infrared imagery from the operational weather satellites and microwave imagery from experimental satellites (when available).

Snow data were based on the operational snow product created by NOAA. These data were digitized from the NOAA/NESDIS (National Environmental Satellite Data and Information Service) Northern Hemisphere Weekly Snow and Ice Cover Charts prepared by the Synoptic Analysis Branch. Snow cover is estimated by visual inspection of all available visible band satellite imagery on a daily basis.

1.4 Data Set Identification.

5-day averaged ice/snow data in a global equal-angle map with 1 degree increments in latitude and longitude.



2. SPATIAL CHARACTERISTICS

2.1 Spatial Coverage.

Global (90 degrees S - 90 degrees N).

2.2 Spatial resolution.

One degree in latitude and longitude.



TEMPORAL CHARACTERISTICS

3.1 Temporal coverage.

July 1983 - December 1990 (continuing product)

3.2 Temporal Resolution.

5 days



4. INSTRUMENT DESCRIPTION

4.1 Mission Objectives.   N/A

4.2 Key Satellite Flight Parameters.   N/A

4.3 Instrument Description and Data Characteristics.   N/A

4.4 Measurement Geometry.   N/A



5. DATA PROCESSING SEQUENCE

5.1 Processing Steps and Data Sets.

The ISCCP ice/snow data are based on the weekly analyses of snow and ice data prepared by the Navy and NOAA.

The sea ice data are obtained from the Navy/NOAA Joint Ice Center and represent a digital version of the weekly analyses issued as paper maps since 1972. The weekly analyses combine four types of data: shore station reports, ship reports, aerial reconnaissance and satellite image analysis. A major contribution (90-98%) to the analyses comes from satellite based information: visible/infrared imagery from the operational weather satellites and microwave imagery from experimental satellites (when available). If data do not arrive during the analysis cycle, older values are retained. All these data are combined by analysts and contoured to produce sea ice charts.

The analysis grid has constant latitude increments of 0.25 degrees and variable longitude increments such that the spatial resolution is better than 15 nautical miles (1853 meters) and the number of longitude increments is an integer divisor of 180 degrees. This results in longitude increments varying between 0.25 degrees near 45 degrees latitude to 30 degrees at the pole.

The original snow data are the operational snow product produced by NOAA, and these data are digitized from the NOAA/NESDIS Northern Hemisphere Weekly Snow and Ice Cover Charts prepared by the Synoptic Analysis Branch. Snow cover is estimated by visual inspection of all available visible band satellite imagery on a daily basis. If cloud cover is persistent, older observations are retained. For the unilluminated portions of the polar regions, snow cover is assumed to be complete and constant. The snow charts are prepared in a polar stereographic projection at 1:50,000,000 scale.

The digital version of the snow cover charts is reduced to an 89 x 89 point grid covering the northern hemisphere in a polar stereographic projection. The effective resolution of each grid cell is about 150 kilometers (km) at low latitudes to about 200 km near the pole. Each cell is declared to be snow covered if the snow cover on the analysis chart is equal to or greater than 50%.

5.2 Special Corrections/Adjustments.

The original NOAA sea ice and snow data were reformatted to a uniform grid, compatible with the ISCCP analyses grids and to uniform time spacing compatible with the cloud analysis cycle (5 days). Moreover, the two data sets were merged into a single data set. The ISCCP data set is contained in a new map grid that is lower resolution than the original sea ice grid and approximately the same resolution as the original snow grid.

Sea ice concentrations in the ISCCP version are preserved by calculating the average of all the sea ice grid values falling into a particular ISCCP grid cell. The center coordinates of the ice grid cells are used to determine whether they are within the ISCCP grid. Snow cover is simply indicated as present whenever the corresponding original cell contained snow. Correspondence is determined by locating the original snow grid cell with its center nearest the center coordinates of the ISCCP map grid.

The ISCCP snow/ice data are also arranged in uniform time intervals of 5 days. The original data sets represent weekly time intervals that are offset from each other: the sea ice data sets for the two polar regions are offset by 2 days, while snow data are not synchronous with either ice data set. The merged data are created by identifying each original ice/snow data set by its center date and each merged version by its center date. The merged data then contain those values from the ice/snow data set with the nearest center date. The original time intervals of each data set merged into the ISCCP version are indicated in the prefix of each data record; thus, the original time intervals can be reconstructed from the ISCCP data.

5.3 Processing Changes.

Information not available.



6. QUALITY ASSESSMENT

6.1 Data Validation by Producer.

Information not available.

6.2 Confidence Level/Accuracy Judgment.

Because the analysis of snow cover is to a large extent a subjective process, it is not surprising that some systematic changes in the analyses have been noted between the earliest charts and contemporary analyses. Part of the differences can be attributed to improved satellites and sensors and part attributed to increased experience and more attention to detail, especially outside North America. Early in the record the Himalayan region was particularly susceptible to such inconsistencies (Matson and Wiesnet, 1981).

6.3 Usage Guidance.

The ISCCP version of ice/snow data are created to help discriminate between ice/snow cover and clouds in performing cloud analysis of operational satellite imagery.



7. CONTACTS FOR DATA PRODUCTION INFORMATION

7.1       User Services Branch
            NOAA/NESDIS/NCDC
            Satellite Data Services Division (SDSD)
            Princeton Executive Square, suite 100
            Washington, DC 20233
            Commercial and FTS: (201) 763-8400
            Telex: 248376 OBSWUR
            Fax: (301) 763-8443

7.2       ISCCP Ice/Snow Data Producer
            Dr. William B. Rossow
            ISCCP Global Processing Center
            NASA Goddard Institute for Space Studies
            2880 Broadway
            New York, NY 10025
            Commercial and FTS: (212) 678-5567

7.3       Original Sea Ice Data Producer
            Navy/NOAA Joint Ice Center
            4301 Suitland Road
            Washington, DC 20390
            U.S.A.
            Commercial and FTS: (301) 763-5972

7.4       Original Snow Data Producer
            Synoptic Analysis Branch
            NOAA/NESDIS
            Washington, DC 20233
            Commercial and FTS: (301) 763-8444



8. OUTPUT PRODUCTS AND AVAILABILITY

8.1 Tape Products

      8.1.1 ISCCP Ice/Snow Data Tape, Level 3

      Medium/Specification: 9-track, 6250-bpi tape

      Format and Content: The basic tape characteristics are as follows:

No. of Files Contents
------------ -----------------------------
2 Header files in ASCII
1 Ancillary data file in ASCII
2 Ancillary data file in BINARY
110 Ice/snow data files in BINARY


The number of ice/snow data files on the tape depends on the amount of data available. In all files each record is 13040 bytes long.

The first ancillary data file contains the cell-center longitudes for the equal-area map cells replicated to each latitude and longitude in the equal-area map grid. This data file is given in ASCII. The next two ancillary data files in binary contain the land/water/coast map and the mean topographic height map. All ice/snow data files in binary are 5 records in length and contain one global map of ice and snow cover conditions.

All data are presented in a global equal-angle map with 1 degree increments in latitude and longitude. Cells are arranged, starting at the south pole and the Greenwich meridian, in order of longitude increasing eastward and latitude increasing northward.

Data Quantity/Rate: Two 9-track, 6250-bpi tapes contain data for the period July 1983 - December 1990.

Status: NCDS will continue to support this data set.

8.2 Film Products. None

8.3 Other Products.

      8.3.1 The ISCCP-C2 CD-ROM

Medium/Specification: CD-ROM in ISO 9660 standard.

Format and Content: The data on this disk consist of the ISCCP-C2 data, read routines, and associated documentation. These data include the TIROS Operational Vertical Sounder (TOVS) and the ISCCP Ice/Snow measurements. Documentation for ISCCP level C1, ISCCP TIROS Operational Vertical Sounder, and the ISCCP Ice/Snow data are also included.

Quantity/Rate: 1 CD-ROM disk.

Status: Release date for this product is scheduled for late Spring 1992.

Plans/Schedule: Users interested in this product should contact the NCDS/Goddard DAAC User Support Office for more details.



9. DATA ACCESS

9.1 Archive Identification

    9.1.1

            User Services Branch
            NOAA/NESDIS/NCDC
            Satellite Data Services Division (SDSD)
            Princeton Executive Square, Suite 100
            Washington, DC 20233
            Commercial and FTS: (301) 763-8400
            Telex: RCA 248376 OBSWUR or TRT 197683 KWBC
            Commercial and FTS Telefax: (301) 763-8443

9.2 Procedures for Obtaining Data.

Procedures for Obtaining Data. Data are provided by visit, telephone call, or written request to SDSD.

9.3 NCDS Status/Plans.

The NCDS/Goddard Distributed Active Archive Center (DAAC) plans to support all ISCCP ice/snow data. Data for the period July 1983 through December 1990 are currently available from the Goddard DAAC.



10. CONTACTS FOR ARCHIVE/DATA ACCESS INFORMATION

            User Services Branch
            Satellite Data Services Division (SDSD)
            NOAA/NESDIS/NCDC
            Princeton Executive Square, Suite 100
            Washington, DC 20233
            Commercial and FTS: (301) 763-8400
            Telex: RCA 248376 OBSWUR or TRT 197683 KWBC
            Commercial and FTS Telefax: (301) 763-8443

            Goddard DAAC User Support Office
            Code 935
            NASA Goddard Space Flight Center
            Greenbelt, Maryland 20771
            Commercial and FTS: (301) 286-3209
            INTERNET: NCDSUSO@NSSDCA.GSFC.NASA.GOV
            NSI DECnet: NCF::NCDSUSO



11. REFERENCES

11.1 Satellite/Instrument/Data Processing Documentation

a.  Rossow, W.B., L.C. Garder, P-J. Lu and A.W. Walker, 1991. "International Satellite Cloud Climatology Project (ISCCP) Documentation of Cloud Data." WMO/TD No. 266 (revised). World Meteorological Organization, Geneva, 76 pp. plus three appendices.

b.  Rossow, W.B., E. Kinsella, A. Wolf, L. Garder, July 1985, revised August 1987. "International Satellite Cloud Climatology Project Description of Reduced Resolution Radiance Data." WMO TD-No. 58, World Meteorological Organization/ International Council of Scientific Unions.

11.2 Journal Articles and Study Reports

a.  Dewey, K.F., 1987. "Satellite-Derived Maps of Snow Cover Frequency for the Northern Hemisphere," J. Climate Appl. Meteor., 26:1210-1229.

b.  Dewey, K.F., and R. Heim, Jr., 1982. "A Digital Archive of Northern Hemisphere Snow Cover, November 1966 through December 1980," Bull. Amer. Meteor. Soc., 63:1132-1141.

c.  Matson, M., C.F. Ropelewski, and M.S. Varnadore, 1986. "An Atlas of Satellite-Derived Northern Hemispheric Snow Cover Frequency," NOAA Atlas, U.S. Dept. of Commerce, Washington, D. C., 75 pp.

d.  Matson, M., and D. R. Wiesnet, 1981. "New Data Base for Climate Studies," Nature, 289:451-456.

e.  Schiffer, R.A., and W.B. Rossow, 1983. "The International Satellite Cloud Climatology Project (ISCCP): The First Project of the World Climate Research Programme," Bull. Amer. Meteor. Soc., 64:779-784.

f.  Schiffer, R.A., and W.B. Rossow, 1985. "ISCCP Global Radiance Data Set: A New Resource for Climate Research," Bull. Amer. Meteor. Soc., 66:1498-1505.

11.3 Archive/DBMS Usage Documentation

a.  Olsen, L.M, J.W. Closs, and F.E. Corprew, November 1991. "NASA's Climate Data System Primer: Version 4.0." EOS DAAC, NASA Goddard Space Flight Center, Greenbelt, Maryland.

b.  WCRP, 1982. "The International Satellite Cloud Climatology Project (ISCCP) Preliminary Implementation Plan (Rev. 1)," WCP-35, World Meteorological Organization, Geneva.



12. RELATED DATA SETS

The original NOAA snow and ice data, on which the ISCCP ice/snow data are based, are archived at and can be obtained from NOAA/NESDIS/SDSD. Information about the following related data sets is available through NCDS: the Electrically Scanning Microwave Radiometer (ESMR), the Scanning Multichannel Microwave Radiometer (SMMR), and the Special Sensor Microwave Imager (SSM/I).



13. SUMMARY/SAMPLE

A sample plot is available for the ISCCP Ice/Snow data set. It is accessible via the "Display Demonstration Plot..." option of the NCDS GRAPHICS Subsystem. To view this plot, specify the plot file ISCCP_IS.



14. NOTES

None.