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26 Sep 2020
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Unable to open ASCAT gribs 2 years 1 month ago #631

  • mgold
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Hello, I am attempting to open the ASCAT microwave scatterometer files in Grib2 format that NOAA derives from the European METOP A&B satellites. Those files are found here ftp.ocean.weather.gov/data/ascat_ab/ I am encountering an error when reading them. (See attached image) It would be really useful to compare numerical model data with actual recorded winds from these satellites. I am using Xygrib 1.2.6. (I am able to open them in NASA's Panoply viewer www.giss.nasa.gov/tools/panoply/download/)
Thank you!

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Last edit: by mgold.

Unable to open ASCAT gribs 2 years 1 month ago #632


There are a number of reasons for deciding not to handle ASCAT data in XyGrib.

The ASCAT data variables are not the same ones used for forecast wind variables. Therefore the ASCAT gribs are not standard forecast gribs. The data is partially corrupt and the bad pixels need to be masked out using the accuracy variable in the ASCAT data. Then measurement errors (biases) need to be corrected by some algorithms. To display ASCAT in XyGrib would require a specific module for ASCAT as the current wind modules can not handle this data. (Panoply just displays the data in its raw state without any processing or correcting).

XyGrib tries to be a middle-of-the-road visualisation and tool for reading forecasts in Grib format without branching off as a Swiss Army Knife toolbox for all Grib data including non forecast data such as ASCAT or other gridded raw measurement data.

The ASCAT data is used (after masking out corrupted data and bias correction) as part of the data assimilation providing the 6 hourly analyses (the zero hour of forecasts). This is probably as close as one can get to real-time data for any point on the globe. ASCAT covers a point only about once a day if I remember correctly. I would suggest to take care in using raw ASCAT data as a wind-meter.

This is all just a best judgement call, and it is happily open for debate.


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