Issues about fog composites

[augustou18]

I would like to ask what is the physical significance of the results generated by ahi/hsd's fog composites. The 3D matrix does not seem to confirm the exact distribution of this fog. Is there something inappropriate in our approach？

[djhoese]

@augustou18 Could you please provide the code you are running to generate the data/image you're looking at and include the exact composite name you are loading?

[augustou18]

@djhoese Hi, djhoese. The composite output fog is a three-dimensional(3 bands) matrix, what is its physical meaning?

[djhoese]

What fog composite are you talking about? Please answer my questions above. My understanding is you are providing Satpy data as AHI HSD files and generating a "fog" composite. Could you please show me the code you are running to do this?

[ZitaTan]

@djhoese Hi, djhoese. I’m using AHI HSD files and generating a "fog" composite too. I get a "fog" image using "scn.load(['fog'])", Could you please tell me what the colors on the picture represent? Thanks.

[mraspaud]

@ZitaTan I think the fog composite in satpy is the 24h microphysics, which you can read more about here https://resources.eumetrain.org/rgb_quick_guides/quick_guides/24MicroRGB.pdf

[djhoese]

Note that there is always a chance our recipe was implemented poorly so please let us know if something looks off. One thing I noticed is that the AHI configuration specifically has difference channels used for the 10.8um in the two differences. See:

satpy/satpy/etc/composites/ahi.yaml

Lines 123 to 135 in 394add5

	fog:
	compositor: !!python/name:satpy.composites.GenericCompositor
	prerequisites:
	- compositor: !!python/name:satpy.composites.DifferenceCompositor
	prerequisites:
	- name: B15
	- name: B13
	- compositor: !!python/name:satpy.composites.DifferenceCompositor
	prerequisites:
	- name: B14
	- name: B11
	- name: B13
	standard_name: fog

Instead of using B13 for both differences, it uses (B15 - B13) for red and (B14 - B11) for green (instead of B13 - B11). I think this is expected for AHI given the goals of the composite and the properties of those bands. Night microphysics is configured similarly. I'm not a scientist, but this is what I remember from past discussions.