Interference of Satellite Dust Detection by Water Vapor

Scientific problem: Observed satellite imagery detects blowing dust, a natural aerosol, in reflective bands during sun-up on 12 UTC 4 August 2016 over Saudi Arabia. However, no signal of blowing dust was evident in the satellite brightness temperature (Tb) split window difference (SWD): Tb(10.7 µm) – Tb(12.0 µm).

Hypothesis: Values of the SWD are sensitive to both blowing dust and water vapor. We propose that if a layer of blowing dust is contained within a “deep enough” layer of water vapor, then the values of SWD will be dominated by water vapor and not blowing dust.

Conclusion A: Results from idealized simulations suggest that there exists the possibility for blowing dust to be evident in reflective bands during sun-up and at the same time be non-evident in the Tb(10.35)-Tb(12.3) –or comparable difference—if the blowing dust layer is within a layer of water vapor that is deep enough and has mixing ratio values large enough. Further, results suggests that Tb(10.35) responds more to dust while Tb(12.3) responds more to water vapor.

Conclusion B: WRF-CHEM results suggest that the water vapor existed in a layer that was deep enough; had values of total precipitable water that were large enough, and that the dust layer had values of aerosol optical depth small enough to prevent dust from being evident in the SWD. That is, water vapor masked, or prevented, the detection of dust within imagery obtained by a satellite platform for the 4 August 2016 case.

Conclusion C: All studies--idealized, NUCAPS, and WRF-CHEM simulations--suggest water vapor can mask the detection of dust by satellite by dominating the signal in infrared dust detection algorithms.

Presentation request: Poster