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  1. What is the reference height of the QuikSCAT data?

    2. "The adopted reference height for all wind vectors is 10 meters." (QuikSCAT User's Guide, section 1.2.4)

  1. Are wind directions given using oceanographic or meteorological convention?

    2. "The oceanographic, or flow vector, convention for wind direction is adopted for QuikSCAT. Under this convention, a wind direction of 0 degrees implies flow toward the north." (QuikSCAT User's Guide, section 1.2.3)

  2. Why do the wind directions point all over the place?

    3. You may have a problem with your software. Are you using the first ambiguity in each file instead of the one selected by the ambiguity removal algorithm?

    The first ambiguity in each wind vector cell contains the solution with the greatest likelihood estimator (max_likelihood_est). This is not the same as the selected ambiguity, which is found by using wvc_selection. Please refer to the QuikSCAT User's Guide for more information on the wvc_selection SDS.

  3. Why is there a data gap annually around November 17?

    4. To minimize the chance of damage during the Leonid meteor shower, the solar panels on the QuikSCAT spacecraft are rotated to present the minimum cross-sectional area to the direction of the meteor flow. Also, the instrument high voltage is turned off to prevent possible shorting caused by plasma clouds generated by meteor impacts.

  4. I ran the make file to compile and link the read software. Why did I get:

    ld: fatal: library -lmfhdf: not found
    5. Before running make, please edit the Makefile. Make sure that the location of the HDF library is correct. The Makefile is currently set to /usr/local/hdf, but your HDF library could be elsewhere. Point to that location.

    Also, the HDF library must be installed properly on your system before you can compile this program. For more information on HDF please refer to the National Center for Supercomputing Applications (NCSA) at http://hdf.ncsa.uiuc.edu

  5. The read software compiled correctly and worked up until SDS .... However, it then segementation faults. Why?

    6. The stacksize on your platform may not be large enough. Try setting the stacksize to 65536 kbytes.

    On SGI's and SUN's, you can change the stacksize by adding the following line to your .cshrc file:

    limit stacksize 65536k
    If you still encounter problems after changing the stacksize, please contact the PO.DAAC QuikSCAT Data Team with the specific details of your problem.

  6. Why does ave_vecmap.pro produce a map over Southern California's coast with most of the vectors pointing North and just one somewhere in the middle pointing East?

    7. Use caution when interpreting the results produced by the IDL program ave_vecmap.pro; some artifacts may affect the map. Artifacts may be due to the following causes:
    • the binning algorithm leaves some isolated cells empty, because grid size and data spacing are almost, but not exactly, identical. Variables affected are asc_u, des_u, asc_v, and des_v.
    • when the ascending and descending grids are averaged, a later empty cell in a later neighborhood acquires the wind vector of the earlier cell, about 1/2 day earlier. This happens because Level 3 files contain only the latest measurement for each day. Since QuikSCAT orbit is sun-synchronous, the local time of the samples is about the same every revisit.

    Easy 'solutions' to the problem would be to 'fill' the isolated empty cells with some average of their neighbors, or to discard cells for which either ascending or descending values are missing.

  7. Do you have software in programming language ... ?
    The PO.DAAC currently provides example QuikSCAT read software in C, Fortran-77 and IDL. No other languages are currently available.
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