The importance of detection thresholds for the quantification of source and timing of high-latitude dust emission using remote sensing

Abstract

Abstract. The observation and quantification of mineral dust fluxes from high-latitude sources remains difficult due to a known paucity of year-round in situ observations and known limitations of satellite remote sensing data (e.g., cloud cover and dust detection). Here we explore the chronology of dust emissions at a known and instrumented high latitude dust source: Lhù’ààn Mân (Kluane Lake) in Yukon, Canada. At this location we combine ground instrumentation, space-based remote sensing platforms, ground-based AERONET data, and oblique camera images to (i) investigate the daily to annual chronology of dust emissions recorded by these instrumental and remote sensing methods (at timescales ranging from minutes to years), and (ii) use data intercomparisons to comment on the principal factors that control the detection of dust in each case. Dust emissions were observed using oblique time-lapse (RC) cameras installed at Lhù’ààn Mân for up to 23 hours a day. These were used as a baseline for analysis of aerosol retrievals from in situ metrological data, AERONET, and co-incident MODIS MAIAC. Use of high-cadence remote camera (RC) data collected during dust events allowed us to optimise the use of combination of date quality (DQ) 1 (aerosol optical depth - AOD) and DQ2 (single scattering albedo and Angstöm exponent) to best represent AOD dust retrievals from AERONET. Nevertheless, when compared with time series of RC data, optimised AERONET data only manage an overall 26 % detection rate for events (sub day) but 100 % detection rate for dust event days (DED) when dust was within the field of view. Here, in this instance, RC and remote sensing data were able to suggest that the low event detection rate was attributed to fundamental variations in dust advection trajectory, dust plume height, and inherent restrictions in sun angle at high latitudes. Working with a time series of optimised AOD data (covering 2018/2019), we were able to investigate the gross impacts of DQ choice on DED detection at the month/year scale. Relative to ground observations, AERONET’s DQ2.0 cloud screening algorithm may remove as much as 97 % of known dust events (3 % detection). Finally, when undertaking an AOD comparison for DED and non-DED retrievals, we find that cloud screening of MODIS/AERONET lead to a combined low sample of co-incident dust events, and weak correlations between retrievals. Our results quantify and explain the extent of under-representation of dust in both ground and space remote sensing method; a factor which impacts on the effective calibration and validation of global climate and dust models.

Analysis of Lhù’ààn Mân’ (Kluane Lake) dust plumes using passive and active ground-based remote sensing supported by physical surface measurements

“…However the subclass scattergrams of the Supplementary material (S4) suggest a more nuanced upper limit threshold: the 𝑈 𝑅𝑆 and 𝑈 𝑁𝑅𝑆 scattergrams, in particular, show upper-limit 𝑣 𝑑𝑢𝑠𝑡 (0) thresholds that can be anywhere in the 10 -11 -10 -10 µm 3 µm -3 range with a respective 𝜏 𝑈 ℓ range of 0.001-0.1. AboEl-Fetouh et al (2020) showed pan-Arctic 𝜏 𝑐 values (regional-scale, multi-year geometric means) that appeared to be robustly sensitive to natural events whose 𝜏 𝑐 variation was as Clay, feldspar, and then quartz minerals are the major constituents of the PM10 dust particles from the emissions in the Kluane Lake region (Bachelder et al, 2020;King, 2023). To derive the mean refractive index and the uncertainty for those values, we followed the method of Baldo et al (2020) volume fraction weighted refractive indices of the minerals found within the dust sampled at the site, through X-ray diffraction, assuming an internally mixed sample (Formenti et al, 2014).…”

“…Publications on the use of AERONET retrievals to characterize the properties of local dust events at high latitudes are rare. Huck et al (2023) employed meteorological measurements, along with AERONET AODs and Angstrom exponents (AOD spectral information), a remote camera and satellite imagery to investigate dust event detection limits in the Lhù'ààn Mân' region. One notable conclusion was that the oblique camera captured many dust blowing incidents that were not being detected by the CIMEL.…”