TROPOMI NO2 columns

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mgeigert
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Joined: Mon May 01, 2023 3:12 pm

TROPOMI NO2 columns

Post by mgeigert »

McIdas-V still is not able to read the TROPOMI netcdf files. This would be a valuable addition. I am sitting next to Brad Pierce at the TEMPO- GeoXO workshop and he suggested that I reach out to you.
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bobc
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Joined: Mon Nov 15, 2010 5:57 pm

Re: TROPOMI NO2 columns

Post by bobc »

Hello,

Thanks for your question about reading TROPOMI data into McIDAS-V. The current McIDAS-V release (version 1.8) does not support TROPOMI data. We added this functionality to our 1.9beta1 nightly build, though, which you can download here. The login and password are both: mcv

I would suggest downloading the version for your operating system without "java11" in the name. For example, on Windows I would suggest McIDAS-V_1.9beta1_windows64_installer.exe. Please note that these nightly builds are automatically created every day with all of the previous day's programming changes. Therefore, not everything has been fully tested.

If you download and install the 1.9beta1 version, you should be able to load TROPOMI data through the General>Files/Directories chooser with the "Grid files (netCDF/GRBI/OPeNDAP/GEMPAK)" data type.

Please let me know if you have any further questions and enjoy the workshop!

Thanks,
Bob Carp
McIDAS User Services
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mgeigert
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Joined: Mon May 01, 2023 3:12 pm

Re: TROPOMI NO2 columns

Post by mgeigert »

Thank you for the link. I was able to download and install the beta software and plot the April 14, 2023 NO2 column density. Unfortunately, there is no layer for the NO2 column with a cloud fraction QA mask of 30%. Is there a way to calculate such a layer using McIdas, or for you guys to post-process the data?
Thanks,
Michael
Attachments
McIdas April 14, 2023 TROPOMI cloud fraction.JPG
McIdas April 14, 2023 TROPOMI NO2 density.JPG
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bobc
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Joined: Mon Nov 15, 2010 5:57 pm

Re: TROPOMI NO2 columns

Post by bobc »

Hi Michael,

McIDAS-V has a variety of formulas packaged with it that allow for operating on the data. One of these formulas, Mask Values, allows for displaying a variable only where the values of another variable are greater or less than a threshold value. Here is the process of displaying TROPOMI NO2 data only where the quality flag values are greater than 0.3:
  1. Load your TROPOMI data source as normal.
  2. From the Field Selector tab of the Data Explorer window, select Formulas on the left side of the window.
  3. Expand Imagery and select Mask Values. Click Create Display. All of the imagery formulas are documented in the User's Guide.
  4. From the Select input window that appears, enter ">" as the comparison, "0.3" as the cutoff, and "1" as useNaN.
    Select input window
    Select input window
    selectInput.png (5.98 KiB) Viewed 433 times
    - "comparison" is the operator to use. Here, we want to only display values greater than the cutoff threshold value.
    - "cutoff" is the actual value we want to use for the masking. Now, NO2 will only display when the pixel has a quality value of greater than 0.3.
    - "useNaN" is how we handle pixels that are masked out (less than 0.3 quality value). A value of 1 sets these pixels to NaN. A value of 0 would set all of these pixels to a value of 0.
  5. Click OK. In the Next Field Selector window, we decide what variable to use for the mask and what variable gets displayed. In the left column for "inputFieldForMask" select the quality value variable. In the right column, select the field to display, which would be the NO2 variable.
Note that you'll likely want to adjust the enhancement and enhancement range after creating the display. The default is to use a grayscale enhancement with a range that matches the min/max found in the layer.

Please let me know if any of this is unclear or if you have any further questions.

Thanks,
Bob
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mgeigert
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Joined: Mon May 01, 2023 3:12 pm

Re: TROPOMI NO2 columns

Post by mgeigert »

Thanks for the instructions. I was able to load the data and use the mask. Attached is the image that I produced. Let me know when beta becomes operational.
Thanks,
Michael
Attachments
April 14, 2023 McIdas TROPOMI NO2.jpg
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bobc
Posts: 987
Joined: Mon Nov 15, 2010 5:57 pm

Re: TROPOMI NO2 columns

Post by bobc »

Thanks for following up, Michael. I'm glad you're able to use McIDAS-V to display and work with your data. I will let you know when the 1.9 stable release is available for download.

Bob
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