Day Moisture RGB

Main applications

• Detection and monitoring of low level (ie total column) moisture fields.

Remarks

• This RGB is newly introduced to MTG FCI.
• Among current GEO imagers, only FCI includes the NIR0.9 band, enabling this RGB.
• Uses a ratio of NIR0.9/VIS0.8 (rather than channel difference).
• Proposed names for this RGB include Water Vapour Transmittance or Total Moisture Imagery to better describe this composite.
• The NIR0.91 channel provides information on vertically integrated water vapour content in the atmosphere (typically dominated by lower tropospheric levels).

Reference: Gao & Kaufman (2003), Water vapor retrievals using Moderate Resolution Imaging Spectroradiometer (MODIS) near-infrared channels, J. Geophys. Res., 108(D13), 4389. https://doi.org/10.1029/2002JD003023.

Development Notes

• Several RGB variants using the NIR0.9/VIS0.8 ratio are under testing.
• Neither the final recipe nor the name of this RGB has been finalized.
• qTPW (quasi-Total Precipitable Water): best visualized through (fast) animations, enabling quasi cloud masking as perceived by the human eye.
• No solar zenith angle correction needed neither for "smt" (NIR0.9/VIS0.8 ratio) nor for the Day moisture RGB.

On the figure below:

• Left image: foehn phase in the early morning -- bright area spreading south.
• Right image: easterly backflow (bora type) over Po Valley in the afternoon -- dark area under clouds advancing westward.
• No clear sign of moisture fields in compared Dust RGB.

14 February 2025, 14:08 & 15:20 UTC

Preliminary FCI Moisture RGB

Colour beam	Channel (difference)	Range min	Range max	Unit	Gamma
Red	NIR0.9/VIS0.8	0.6	1		0.8
Green	NIR0.9/VIS0.8	0.6	1		0.8
Blue	WV7.3	230	270	K	0.3

Météo-France tested three different algorithms to enhance the visualization of moisture fields: two RGB variants and ESSL visualization (using NIR0.9/VIS0.8 ratio):

ESSL Colour Palette Version (Left Image)

• NIR0.9 / VIS0.8 visualized with a colour palette.

RGB Variant 1 (Right Image)

Uses the following RGB configuration:

Colour beam	Channel (difference)	Range min	Range max	Unit	Gamma
Red	VIS0.6	0	100	%	1.4
Green	NIR0.9/VIS0.8	0	100	%	1.0
Blue	WV7.3	270	230	K	3.3

H.-P. Roesli Variant (Middle Image)

Same green and blue component as variant 1, but applies different gamma settings for the blue channel (exact value range is not confirmed).

Colour beam	Channel (difference)	Range min	Range max	Unit	Gamma
Red	VIS0.9/VIS0.8	0	100	%	1.0
Green	NIR0.9/VIS0.8	0	100	%	1.0
Blue	WV7.3	270	230	K	3.3

Next steps / recommendations

• Determine whether this RGB provides significant benefits over a simple SMT (VIS0.9/VIS0.8 ratio) imagery.
• Explore the inclusion of additional channels to diversify input (currently, both red and green beams rely on similar ratio inputs).
• Consider adding cloud-sensitive channels (e.g., NIR1.38, NIR0.91, VIS0.8), as current output may appear overly yellow.