The Dark Target project: Over-land aerosol remote sensing from MODIS and other satellite imagers using LUTs

The Dark Target (DT) retrieval algorithm was developed for Moderate-resolution Imaging Spectroradiometer (MODIS) and derives aerosol optical depth (AOD) and other aerosol properties over global land and ocean. The DT algorithm works by matching satellite-observed, top-of-atmosphere (TOA) reflectance with lookup tables of pre-computed reflectance that represent a variety of aerosol types and AOD loadings. These are in-turn created by passing results of particle scattering (SCA) codes as inputs into Radiative Transfer (RT) codes. In the early 2000s, there was not a single combined code that provided the flexibility, accuracy, and completeness which I desired for, so I had to combine SCA and RT codes myself. Enter the 2^nd edition of Liou’s most famous textbook. Following its clear instructions for integration over aerosol size distributions and converting between scattering efficiencies and Legendre polynomials, I was able to transform SCA outputs into RT inputs, thereby creating “Liou-up Tables” (LUTs).

Because of its relative simplicity and flexibility, DT has been implemented on additional satellite imagers with MODIS-like wavelength information. This includes similar sun-synchronous low-earth orbit (LEO) sensors such as Visible-Infrared Radiometer Suite (VIIRS) on Suomi-NPP and NOAA-20, as well as Geostationary (GEO) imagers such as Advanced Baseline Imager (ABI) on GOES-R series (East and West) and Advanced Himawari Imager (AHI) on the Himawari series. The continuation of LEO leads to long-term data record (now at 22 years and counting), and the GEO sensors provide characterization of rapid aerosol changes and the aerosol diurnal cycle. In this presentation I highlight some of my efforts with the DT LUTs and a status update about the current algorithm and available products.