VIIRS swath to grid - missing display types

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hproe
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VIIRS swath to grid - missing display types

Post by hproe »

Hi -

Some nightlies have passed since I processed VIIRS data. With the nighty of 22 Feb I see that the swath-to-grid method has been moved under 'Imagery > JPSS Functions ...', which is fine. However, it only offers the simple Image display types. 3 Color (RGB) Image (over topography) are missing. For me this becomes. handy when doing non-standard RGBs.

cheers, HP
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bobc
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Re: VIIRS swath to grid - missing display types

Post by bobc »

Hi HP,

I just made a code change that will appear in the next nightly (build date 02/25/2020). I made the following changes:

  1. Added "3 Color (RGB) Image over topography" as a valid display type for the VIIRS True Color, Night Microphysics, and Dust RGBs.
  2. Added "Image Display Over Topography" as a valid display type for VIIRS NDVI.

I see that you specifically mentioned the "3 Color (RGB) Image over topography" display type was missing from the "Swath To Grid" formula. The swathToGrid function only accepts one field, so I'm a bit confused as to how the RGB display types would be valid, since RGBs require 3 fields. Could you please elaborate more on how you were previously able to create a RGB display directly from "Swath To Grid"?

Thanks,
Bob Carp
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hproe
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Re: VIIRS swath to grid - missing display types

Post by hproe »

Hi Bob -
Sorry for this post. I have missed to look deeper into the RGB formulae that have recently been added for ABI, AHI, VIIRS (and SEVIRI). This makes my request obsolete. In the past I have used swath-to-grid to produce RGBs for VIIRS data by using my set of SEVIRI formulae like:
data set > swath-to-grid (display: RGB composite or 3 Color RGB) > Formulas > SEVIRI RGB > apply bands

I see now that the JPSS formulae include the swath-to-grid pass. They are all for the M-bands (750m). It would be nice to also add the Natural-Colour RGB for the I-bands I3,I2, I1. What do you think?

cheers, HP
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bobc
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Re: VIIRS swath to grid - missing display types

Post by bobc »

Hi HP,

No worries. Yes, we've been adding a lot of RGBs and other channel combination formulas/derived products to McIDAS-V. Documentation on many of the AHI and VIIRS RGBs seems to be pretty scarce without anything deemed to be that official. I did just find a couple EUMeTrain recipes for VIIRS RGBs. One of them is the True Color RGB. I noticed that this recipe says that you should scale the M5, M4, M3 reflectances between 0 and 110%. I'm working on updating that function right now. The recipe also says to use a piecewise linear stretch, which I'm investigating, but I don't believe there's an easy way to apply that. The gamma of 3 does give a pretty nice image though. In the image below, the left panel is the VIIRS True Color RGB formula included in the nightly, on the right is the output if you do the rescaling and gamma correction:
Left=current function<br />Right=rescaled with gamma 3
Left=current function
Right=rescaled with gamma 3

This is without modifying the common gamma value in the Layer Controls. We'll have to discuss if applying this gamma to the function is appropriate to do or not.

As for the SVI natural color RGB, this could definitely be added. Do you know if this is documented anywhere? I see the bands to use (Red=I3, Grn=I2, Blu=I1), but I'm not sure if any rescaling or gamma corrections are involved. Just as an FYI, the "VIIRS Day Land Cloud Fire RGB" formula uses I bands (I1, I2, and I4), but the function applies rescaling and a gamma correction to the red (I4) band, so it can't be used generically like the original VIIRS_M_RGB function from McV 1.8 was.

If you notice any other RGBs that are missing from any other satellite/instrument, please let me know that as well.

Thanks,
Bob
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hproe
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Re: VIIRS swath to grid - missing display types

Post by hproe »

Hi Bob -

From my experience I would not re-scale and gamma correct the SVI Natural Colour RGB. The gamma correction should be done in the Layer Control, i.e. left to the user. I often find that I have to fiddle a bit with gamma, depending on what feature(s) I would like to have enhanced, e.g. (thin) dust with a gamma <1.

For new RGB ideas see the attached text file that has formulae for a 'greened AHI True Colour (including piece-wise linear enhancement) and for ABI Cloud Phase and Cloud Type.

For the Cloud Phase I have a powerpoint, which I have done a couple of years ago for the Tokio RGB workshop - the imager there is VIIRS, however. Both Cloud RGB receipts very much depend on lighting conditions and usually need some fiddling with ranges and gammas. Tell me where to upload the powerpoint, if you are interested.

As regard piecewise-linear enhancement, I am not enthusiastic about it. Usually applying a gamma is doing the job. I have done so when I recently produce a long AHI True Colour movie of the Australian fires.

best, HP
Attachments
AHI-ABI-RGBs.rtf
(5.38 KiB) Downloaded 101 times
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bobc
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Re: VIIRS swath to grid - missing display types

Post by bobc »

Hi HP,

Thanks for your thoughts on this as well as your AHI-ABI-RGBs code! It's always great to hear from real users of the data to get their input. I'll compare what we have now with what's in that document. I would definitely be interested in the PowerPoint presentation. You could post it to our anonymous ftp. Here are some instructions for doing that:

Code: Select all

ftp ftp.ssec.wisc.edu
user: anonymous
password: your_email_address
bin
cd pub/incoming
put filename
bye

Please let me know the name of your PowerPoint file and I'll pick it up and give it a look.

Thanks again,
Bob
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hproe
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Re: VIIRS swath to grid - missing display types

Post by hproe »

power point is uploaded: VIIRS.odp
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bobc
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Re: VIIRS swath to grid - missing display types

Post by bobc »

Thanks, HP. I'll check this VIIRS cloud phase RGB out. I just committed code to add the VIIRS SVI Natural Color RGB formula to McV. This will be available in tomorrow's (02/29) nightly build.

Bob
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bobc
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Re: VIIRS swath to grid - missing display types

Post by bobc »

Hi again HP,

Just as another update, I added a few more RGB functions today that will appear in tomorrow's (03/03) nightly:

From your AHI-ABI-RGBs.rtf attachment:
ABI Cloud Type RGB

From the VIIRS PowerPoint you posted to ftp:
VIIRS Cloud Phase RGB
VIIRS Cloud Type RGB

Thanks again for your contributions to the RGB functions. Having your MSG plugin was a great template to follow for the other satellites/instruments.

Bob
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hproe
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Re: VIIRS swath to grid - missing display types

Post by hproe »

Hi Bob -

I'm pleased that you could make good use of my RGB formulas.

I have checked the 2 SVI formulas. They are not working properly for me, like:

1) I have used the path
Imagery > JPSS Functions (Under Development) > VIIRS Natural Color SVI RGB

2) clicking the formula nothing happens (e.g. greying at least)
3) thumbnail shows (too) large area and I can draw selection rectangle anywhere
4) at bottom of thumbnail appears text: "Image values must be mapped to ed, Green or Blue only"
5) during processing RAM is exhausted: memory indication in bottom left corner RED
6) image layer appears in Legend, but no image

VIIR NDVI has similar behaviour, but outputs something like
NDVI.png

cheers,HP
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