The Dark Target Algorithm for Observing the Global Aerosol System: Past, Present, and Future

Abstract

The Dark Target aerosol algorithm was developed to exploit the information content available from the observations of Moderate-Resolution Imaging Spectroradiometers (MODIS), to better characterize the global aerosol system. The algorithm is based on measurements of the light scattered by aerosols toward a space-borne sensor against the backdrop of relatively dark Earth scenes, thus giving rise to the name “Dark Target”. Development required nearly a decade of research that included application of MODIS airborne simulators to provide test beds for proto-algorithms and analysis of existing data to form realistic assumptions to constrain surface reflectance and aerosol optical properties. This research in itself played a significant role in expanding our understanding of aerosol properties, even before Terra MODIS launch. Contributing to that understanding were the observations and retrievals of the growing Aerosol Robotic Network (AERONET) of sun-sky radiometers, which has walked hand-in-hand with MODIS and the development of other aerosol algorithms, providing validation of the satellite-retrieved products after launch. The MODIS Dark Target products prompted advances in Earth science and applications across subdisciplines such as climate, transport of aerosols, air quality, and data assimilation systems. Then, as the Terra and Aqua MODIS sensors aged, the challenge was to monitor the effects of calibration drifts on the aerosol products and to differentiate physical trends in the aerosol system from artefacts introduced by instrument characterization. Our intention is to continue to adapt and apply the well-vetted Dark Target algorithms to new instruments, including both polar-orbiting and geosynchronous sensors. The goal is to produce an uninterrupted time series of an aerosol climate data record that begins at the dawn of the 21st century and continues indefinitely into the future.

Changes in Clear‐Sky Shortwave Aerosol Direct Radiative Effects Since 2002

“…Furthermore, the AOD trends are widespread, uniform and mainly occur over the SH oceans (Figure 1b). Positive AOD trends over the southern oceans are also apparent in Remer et al (2020; see their Figure 12). Since the CERES results do not show this unexpected behavior, we cannot exclude MODIS calibration drift as a possible cause, as recently suggested by Bellouin, Davies, et al (2020), who found similar results.…”

Observation and modeling of the historic “Godzilla” African dust intrusion into the Caribbean Basin and the southern US in June 2020

“…The NASA GEOS is a global Earth system model that includes components for atmospheric circulation and composition, ocean circulation and biogeochemistry, land surface processes, and data assimilation (Rienecker et al, 2011). The coupled atmospheric constituent module within the GEOS architecture most relevant to this study is an aerosol module based on the Goddard Chemistry Aerosol Radiation Transport (GOCART) model (Colarco et al, 2010).…”

Biomass Burning and Gas Flares Create the Extreme West African Aerosol Plume Which Perturbs the Hadley Circulation and Thereby Changes Europe’s Winter Climate

“…It can be identified on the monthly mean 0.55 micron AOD data from MODIS [15] on the NASA Terra satellite distributed via NASA Giovanni. The uncertainty in the AOD measured by this satellite is "τ=±0.05 ±0.15τ over land" and the AOD retrievals can be used in monitoring the aerosol radiative forcing of the global climate [16] [17].…”