Disappearing Dust Plumes: Exploring the Roles of Water Vapor and Dust Properties in Detection from Satellite Observations

Many strategies used for the detection of dust plumes from satellite-borne instruments rely on differences in brightness temperatures from ~10 and ~12 micron channels. We present a case study where this approach failed to detect a dust plume observed over Saudi Arabia. Based on the meteorological conditions, we hypothesized that interference from water vapor could reduce the brightness temperature difference sufficiently to obscure the dust, even when using the DEBRA (Dynamic Enhancement with Background Reduction Algorithm; Miller et al., in review) methodology to enhance detection over bright surfaces. Further, we explored the impact on brightness temperature differences of assumed dust physicochemical properties, including sphericity, size distribution, and refractive index. Of particular significance is the absorption by dust in these relevant wavelengths. Recent work (DiBiagio et al., 2017) suggests blowing dust has site-specific complex indices of refraction that can vary considerably from commonly-assumed values. In this work we conducted simple radiative transfer modeling over the relevant parameter space, demonstrating combinations of environmental and dust properties that result in near-zero brightness temperature differences that lead to non-detection of dust events, and apply these findings to our case study example.