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GLAS Standard Data Products for Distribution by NSIDC

This presentation discusses the GLAS standard data products for distribution, including the HDF-EOS swath format for level 3 products and the custom SCF format for level 1 and 2 products. It highlights the advantages of each format and compares data access timing. The presentation also addresses specific concerns with HDF-EOS and provides insights from the PO-DAAC experience with HDF data.

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GLAS Standard Data Products for Distribution by NSIDC

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  1. GLAS Standard Data Productsfor Distribution by NSIDC Polar DAAC User Working Group PoDAG Meeting XVI 7 - 9 February 2000 Presenters H. Jay Zwally, NASA/GSFC Anita C. Brenner, Raytheon ITSS

  2. Product Formats • HDF-EOS swath – level 3 • Geophysical and atmospheric parameters • Tailored to parameters required for Interdisciplinary/multi-sensor studies • Customized Science Computer Facility binary stream – level 1 and 2 • Includes data on 3 plus all the lower level raw data and corrections required to produce level 3 • Tailored to mathematical analysis, modeling, detailed surface analysis and comparisons with other altimetry missions and elevation data sets

  3. GLAS Level 3 HDF-EOS swath product contents • Time • Surface characteristics • Location (geodetic latitude and longitude) • elevation • Reflectance • Roughness/slope • Atmospheric parameters • Cloud layer heights • Aerosol layer heights including planetary boundary layer • Thin cloud and aerosol Optical Depth • Polar stratospheric cloud heights/optical depth

  4. Advantages for producing GLAS level 3 product in HDF-EOS • Level 3 parameters are GLAS science products scientists may require for multi-sensor and interdisciplinary studies with other HDF-EOS data sets. • Tools such as WebWinds exist to visualize and compare GLAS results with other HDF-EOS data sets • Files are self descriptive. People used to using HDF will be able to query file contents using tools

  5. GLAS level 1and 2 SCF custom formatted products

  6. Advantages for producing GLAS level 1 and 2 products in custom SCF format • SCF format is flat integer binary and conforms with IEEE standards • The polar altimetry user community is used to using data in a format similar to our internal SCF format. • The JASON (the ocean altimetric mission NASA/CNES ) and ENVISAT( the ESA ERS-2 follow-on) missions are planning on putting their data in flat IEEE binary format. • It will be compatible with all existing historic altimetry data. No plans exist to put this data in HDF or HDF-EOS.

  7. Advantages for producing GLAS level 1 and 2 products in custom SCF format (cont) • Tools for displaying HDF-EOS swath data display images and do not give value-added plotting capability to profile data. • HDF or HDF-EOS adds complexity to accessing the data for researchers – it is a language not a format • requires ECS toolkit or 3rd party software • HDF-EOS routines are complicated to use require days to program instead of minutes by experienced matlab and IDL programmers. • All tools access the data one parameter at a time so access time is excessive • File sizes are twice as large as for custom SCF

  8. Data Access Timing Comparisons 6000 sec of data Using IDL to access both HDF-EOS_SW file and SCF format file

  9. Advantages for producing GLAS level 1 and 2 products in custom SCF format (cont) • HDF-EOS long-term usability is a concern • HDF-EOS is a subset of HDF 4.0 • HDF 5.0 is the current version and is NOT backward compatible with HDF 4.0 • NCSA* promises only to maintain current HDF version • 3rd party tools that now read HDF 4.0 are being updated to read HDF 5.0. There is no guarantee that they will maintain versions to read HDF 4.0 • HDF-EOS is addressing some of this concern by arranging with GSFC to maintain HDF 4.0 *NCSA – National Center for Supercomputing Applications

  10. GLAS specific HDF-EOS concerns • Altimeter data is not swath but a single point. We are forced to store it like multi-band images, however each "band" is really a different geophysical parameter. • The documentation and format is so non-intuitive for profile data that it took months working with NSIDC to produce one sample file in HDF-EOS swath product. • HDF-EOS Tools do not parse and manipulate data in an effective method for analysis of altimetry data • If data is stored in single dimension, (sec) Arrays with full-rate parameters are very long and inefficient to access. • If data is stored in 2-D arrays (40, n sec) the current tools will not properly parse and display the data in a manner appropriate for altimetry uses.

  11. PO-DAAC experience with HDF data • NSCAT, QuikSCAT and some AVHRR data only available in HDF • PO-DAAC supplies HDF subsetting utility • Prevalent use is not to subset data, but to output the whole data set in a flat binary format • Users then use the flat binary format • GOSTA (Global Ocean Surface Temperature Analysis) – CD released in HDF • Community and international collaborators complained so much that they were forced to release a new CD with data in flat binary format

  12. PO-DAAC experience with HDF data (cont) • Survey sent to users asking how they would feel about getting data in net_CDF (an ECS acceptable alternative to HDF) • 4 % positive • 23 % negative • Most sophisticated users fell in this group • Complained about added complexity of anything other than a flat binary format • 24 % neutral • 49 % did not have an opinion

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