On Monday, 11 July from 3:00 p.m. through Wednesday, 13 July until 5:00 p.m. (USA Mountain Time), NSIDC data distribution, services, and Web site will be unavailable to accommodate a major upgrade to our data center. We apologize for any inconvenience this may cause you. Need to talk to us? You can always contact our friendly User Services Office at firstname.lastname@example.org or + 1 303.492.6199.
In this Issue
ARCTIC SYSTEM SCIENCE (ARCSS)
PRODUCTS AND SERVICES
The first in a series of ARCSS CD-ROMs is scheduled to be released in early May. Titled "ARCSS/LAII Data Series Volume 1: Alaska North Slope Data Sampler," the CD-ROM contains data from the North Slope of Alaska, identified by the principal investigators of the ARCSS Land-Atmosphere-Ice Interactions (LAII) Flux Study ("CO2 and Methane Fluxes by Ecosystem Type and Long-Term Feedback Relationships with the Atmosphere") as important to their current and future research. Soil profile and type, climate data, river runoff records, and GIS data from a multitude of studies comprise the contents of the CD-ROM. This CD-ROM will be provided to all ARCSS investigators, and available on request to all interested parties.
If you have specific questions on the data included on the CD-ROM, please contact NSIDC User Services.
If you wish to be notified when the CD-ROM is available, please contact NSIDC User Services.
Other projects to gather data for ARCSS investigators are currently underway, with additional CD-ROM releases anticipated during 1994. The 1992 - 1993 ARCSS Northeast Water Polynya Project (NEW) data will be arriving shortly at NSIDC. Distribution of these data initially will be restricted to NEW investigators; release to the wider Arctic community will follow in about a year. Efforts to acquire data for the Arctic Solar Radiation CD-ROM are being implemented, and we are looking forward to working closely with the future ARCSS Modeling Working Group to help us continue to define data requirements for the "Model Test Kit" on CD-ROM. We will keep you posted on the status of these and other projects in future issues of NSIDC Notes.
The ARCSS OAII Science Steering Committee sponsored an evening open forum during the San Diego AGU/Oceans meeting (21-25 February) to generate interest in and ideas for an "Arctic Shelf-Basin Biological Initiative," led by J. Grebmeier, University of Tennessee Graduate Program in Ecology and T. Whitledge, University of Texas Marine Science Institute. The next step will be formulation of a workshop on this topic in the context of "System Science" and "Global Change." M. Cross and C. Hanson attended the forum in an effort to become familiar with development of the proposed ARCSS initiative from the ground floor.
C. Hanson and R. Barry attended the annual meeting of the Arctic System Science (ARCSS) Paleoclimates of Arctic Lakes and Estuaries (PALE) Principal Investigators, hosted by the Institute of Arctic and Alpine Research (INSTAAR), University of Colorado at Boulder, 4-5 February 1994. The meeting focused on presentation of PALE results to date, and on a program assessment and setting priorities for the coming one to two years. Highlighted topics in the latter portion of the meeting were paleoclimate modeling and integration with proxy data, temporal and spatial coverage of proxy data (what remains to be collected/analyzed to meet the research objectives of PALE), strategies for collating, presenting, and integrating data for paleoclimate proxies and modeling, long-term data access and archiving, and linkages with other components of the NSF-funded ARCSS Program. Hanson presented an overview of the NSIDC ARCSS data management project for the Greenland Ice Sheet Program 2 (GISP2), Land-Atmosphere-Ice Interactions (LAII) and Ocean-Atmosphere-Ice Interactions (OAII) components of ARCSS. The key outcomes of the meeting for NSIDC include meeting the PALE investigators and Science Steering Committee face-to-face as well as learning about their research, obtaining the list of PALE investigators and their contact information, and a scheduled meeting with E. Law-Evans, a PALE postdoctoral modeler on appointment at NCAR. Working with Starley Thompson at NCAR, Dr. Evans will be a key player in the proposed ARCSS-wide Modeling Working Group.
NSIDC, in collaboration with the SSM/I Products Working Team (SPWT), distributed the Equal Area SSM/I Earth Grid (EASE-Grid) Prototype Version 1.0 CD to a selected group of researchers in early February 1994. The EASE-Grid is being developed as a data structure for the distribution of earth-gridded SSM/I data with full global coverage. The purpose of Version 1.0 is to finalize this data structure.
The EASE-Grid provides a data format (binning, gridding and projection) to the general user which maximizes the radiometric integrity of the original brightness temperature values, maintains high spatial and temporal precision, and involves no averaging of original swath data. Version 1.0 of the EASE-Grid contains earth-gridded SSM/I Brightness Temperatures for the full Northern Hemisphere for the period January 13 to February 29, 1988, as well as a limited sample of data in the full global Mercator projection and the Southern Hemisphere projection.
Guidance on the format of Version 1.0 was received from researchers who received the Prototype Version 0.0 CD in 1993, as well as the Polar DAAC Advisory Group (PoDAG) and the NASA/NOAA Pathfinder SSM/I Science Working Group, which has adopted EASE-Grid as the format for the SSM/I Pathfinder Level 3 Products (earth gridded).
For more information, contact: R. Armstrong, at (303) 492-1828 or Internet: email@example.com.
In June 1993, the NSIDC DAAC began research and development of an SSM/I-derived ice edge product. The effort began after NSIDC received a request from Elizabeth Smith (NASA/JPL) for an ice edge product that could be integrated into the Sea Surface Temperature (SST) algorithm being developed by Bob Evans at the University of Miami's RSMAS facility as part of the NASA EOSDIS AVHRR Pathfinder (Oceans Group) activities. The ice edge product would be used as a filter, masking known areas of sea ice from the AVHRR SST retrieval algorithm thereby minimizing any possible contamination of an SST product by the presence of ice.
Shortly after NSIDC User Services received the request for an ice edge product, a working group was formed to determine which data sets archived by NSIDC would satisfy the requirements of the AVHRR Pathfinder Oceans Group. The working group found that no digital sea ice product existed that would be suitable to satisfy their needs. Upon further deliberation, the working group concluded that a monthly averaged sea ice concentration product could be generated easily from the DMSP SSM/I Daily Sea Ice Concentration Grids that were being generated and currently distributed by the NSIDC DAAC on CD-ROM. The monthly averaged sea ice concentration grids would provide the necessary ice extent information required by the SST retrieval algorithm. A review of sea-ice modeling requirements suggested that the monthly concentration grids would be useful for model comparisons and inputs.
IDL procedures were developed to calculate monthly averages from the existing daily averaged SSM/I Sea Ice Concentration grids which were produced using the NASATEAM algorithm (Cavalieri et al., 1986, J. Geophys. Res., 91(C1), p. 975-994; 1994, in prep.). To accommodate as many potential applications as possible, ice extent was delineated based on four concentration values (0%, 5%, 10%, 15%) that define the minimum concentrations included in the averages. These different minima (or "thresholds") were selected to meet the needs of users who have various applications for the data. For example, to minimize any possible contamination of an SST product by the presence of ice, the monthly averages using a 0% threshold may be most suitable. Other users interested in defining the general location of the marginal ice zone might prefer the 15% threshold. Products created using intermediate thresholds can be examined to study the nature of the ice margins and to highlight any residual weather or land contamination.
The monthly averaged data files contain ice concentration values in percent ranging from 0 to 100. A value of -88 (or 168 for unsigned byte data types) indicates a land pixel and a value of -99 (or 157 for unsigned byte data types) indicates missing data.
The grids are 8-bit raster images. Images for the north polar region contain 448 lines with each line containing 304 pixels. Images for the south polar region contain 332 lines with each line containing 316 pixels. The data were transferred into Hierarchical Data Format (HDF) using the National Center for Supercomputing Applications Raster Image Set.
The SSM/I Monthly Averaged Ice Concentration Grids will be available to the public in April 1994.
For further information regarding the availability of these data, contact NSIDC User Services.
In an effort to satisfy the EOSDIS requirement to put all Version 0 data sets into the Hierarchial Data Format (HDF), a subgroup was formed to study and implement this task for point/station/in-situ data. This subgroup comprises members from the NSIDC DAAC, National Center for Supercomputing Application (NCSA), NOAA-National Geophysical Data Center (NGDC), EOSDIS project and Hughes STX.
The subgroup was tasked to survey producers of various type of non-image data sets. Most of the data sets of this type can be described by the term "point data." Point Data are defined as:
Since no previous methods existed to implement point data into HDF, it was proposed that a new storage strategy be developed.
The Historical Arctic Rawinsonde Archive (HARA) was chosen as a test data set because it exemplified point data. The HARA data set is a time series of rawinsonde measurements over several Arctic regions. The format of this data set includes a header record consisting of information about a particular sounding (e.g., station number, latitude, longitude, time and other sounding parameters). The second part of the data, data records, are the actual measurements made as the balloon rose above the Earth's surface.
HDF Vsets were chosen as the best structure to organize the HARA data. The header records were organized as an index or set of search keys that mapped to a specific set of data records. HDF Vsets, are defined as having two components:
For the point data case, the header records are in one Vdata, and the data records in the other Vdata. For a more detailed description of Vsets documentation can be found on NCSA's anonymous ftp server (126.96.36.199).
The Point Data Working Group queried other data centers for previous experience working with such data structures and found that NOAA/NGDC had working software that could reorganize data from one format to any other format, and splitdat splits record headers and data into separate files or Vdatas.
The input data files can be either ASCII or binary files with header records and data records data in varying formats. Historical Arctic Rawinsonde Archive data were transferred by splitdat into HDF. The structure of these HDF files can be 'visualized' as shown.
A visual interpretation of the structure of HDF files.
The HDF utility pntshow takes a vset file created by splitdat and displays the HDF data records according to specified output formats. A specified output format has been saved within the HDF file. The vset file must have been packed by using the HDF utility hdfpack. One can extract the data records and/or display the header records. The data from the HDF file can also be extracted in a user defined format. These ASCII or binary formats can be specified in files defined according to the FREEFORM data description language developed at NOAA/NGDC.
For general information please contact: Nick Sandoval, at (303) 492-5710, or fax: (303) 492-2468, or Internet: firstname.lastname@example.org., or email@example.com.
For technical information on splitdator pntshow please contact: Ted Habermann, NOAA-National Geophysical Data Center (NGDC), E/GC, 325 Broadway, Boulder, CO 80303, or (303) 497-6472 or fax: (303) 497-6513, or Internet: firstname.lastname@example.org, or OMNET: HABERMANN
Figure 1 appears in the hard copy version of NSIDC Notes, No. 8, but is unfortunately unavailable here. It demonstrates the current capabilities to access and graphically display HARA data stored in HDF. The data were retrieved and displayed using the NOAA/NGDC GeoVu Data Access System.
Since August of 1993, NSIDC has been collecting and archiving a bi-polar data set of 1-km HRPT and LAC AVHRR imagery. The archived data is received by HRPT stations at McMurdo, Palmer, Fairbanks, Prince Albert, and TromsØ, and includes LAC images of both polar regions as well.
NSIDC receives most of the data as a polar subset of the Global Land 1-km AVHRR Data Set, currently collected by the EROS Data Center (EDC). Antarctic HRPT data is received from the Scripps Institution. Combined, these two data sets provide nearly complete coverage of both poles' sea ice, land ice, and polar lands at nearly 1-km resolution for all 5 bands of the AVHRR sensor (visible, near-IR, and thermal-IR). Currently, the archive contains data from the Antarctic over the period April 1992 - May 1992, January 1993, and August 1993 to the present. We have nearly complete coverage for the Arctic regions, from August 1993 to the present. Antarctic data for the gap periods between April 1992 and August 1993 are being archived on a continuing basis.
We can now provide the archived data in NOAA's Level format for general distribution. The media for this distribution will be DAT 4 mm magnetic tapes or Exabyte 8 mm magnetic tapes. Further, a catalogue of all archived scenes, with information on location, time of acquisition, image size, and data quality, may now be distributed to any interested party upon request. This will allow potential users of the data set to see what areas are covered, and how frequently they are covered. Browse image data for each image is accessible over the Internet or on a variety of magnetic media. However, the browse data are in HDF format, and potential users of the archive should consider how they will handle the HDF browse imagery on their computing platform. (We will, in general, send browse images prior to any data transfer, to insure that the data are appropriate for the user's needs). One solution we can provide is a procedure file for the IDL software package that will display the browse scenes on some workstations, provided that IDL is installed.
An example of a browse scene generated for the Polar 1-km AVHRR Data Set appears in the hard copy version of NSIDC Notes, No. 8, but is unfortunately unavailable here. Browse images are generated by sampling every fourth pixel from every fourth line of the archived image, and dividing the sensor values by 4.
Parties interested in receiving a copy of the catalogue, browse data, or having other questions about the archive, may contact contact NSIDC User Services.
NSIDC User Services
National Snow and Ice Data Center
CIRES, 449 UCB
University of Colorado
Boulder, CO 80309-0449 USA
phone: +1 303.492.6199
fax: +1 303.492.2468
form: Contact NSIDC User Services
Since Issue no. 4 of this newsletter, NSIDC has offered access to radar altimetry data (gridded data, slope-corrected height profile data, and waveform data) from the Seasat and Geosat missions. NSIDC obtains this data by interacting with the NASA Goddard Space Flight Center data archive managed by Dr. Jay Zwally. However, throughout 1993, access to this data was hampered as NASA modified and improved its data retrieval and visualization software. This process is now complete, and turnaround on users' requests for well-bounded, small- to moderate-sized study regions within the Greenland and Antarctic ice sheets will be much quicker.
We encourage any users interested in receiving satellite altimetry data from ice sheet areas equatorward of 72 degrees north or south to contact us. Within the next two or three months, NSIDC anticipates that it will receive CD-ROMs containing the entire Seasat and Geosat data sets (excluding waveform data) from NASA for distribution. Distribution of these CD-ROMs will address user requests for gridded height data and slope-corrected height profiles over wider areas or time series.
ERS-1 altimetry is also available through NASA, although at present its access will be limited to Principal Investigators on the ERS-1 satellite and their co-workers. NSIDC anticipates a similar level of access to ERS-1 altimetry data, as it has for the previous altimetry missions, by the end of the year, and will be able to distribute that data along the same kinds of guidelines (well-bounded, limited area and limited time- period) that it now requests of its users for the Seasat and Geosat data. ERS-1 CD-ROMs are planned.
For more information, contact: Ted Scambos at Internet: email@example.com or (303) 492- 1113.
NOAA's National Geophysical Data Center (NGDC) has begun processing smooth resolution OLS data as of February 1, 1994. As soon as the inventory and browse functions are operational, archive tapes will be generated and these data will be available. Data for several requests from users have been processed from the backlog of data accumulating since March 1992. NSIDC has successfully transferred data for two data requests via FTP. Users are encouraged to contact NSIDC User Services with potential requests at this time. Requests for data from the backlog will be forwarded to NGDC and processed as time permits.
Processing of DMSP special sensor data (SSM/I, SSM/T and SSM/T-2) is expected to begin this Spring.
For more information, contact Greg Scharfen at Internet: firstname.lastname@example.org or Rob Bauer at Internet: email@example.com or (303) 492-2378.