A NASA LEO/GEO imager Program of Record dataset for cloud properties, Part I: Challenges and approaches to continuity

[11-Jan-2023] Abstract  As the NASA Earth Observing System (EOS) program ages, NOAA's new generation of advanced operational weather satellites are natural successors for extending important imager cloud climate data records begun by MODIS. In addition, many of these low-Earth orbit (LEO) observations are expected to be coupled with like observations from the new generation of advanced geostationary (GEO) imagers (e.g., ABI, AHI, etc.), allowing for the possibility of a consistent LEO/GEO cloud product Program of Record (PoR) that can enable enhanced climate and process studies by NASA investigators and the broader research community. Note that a cloud product PoR is desired to provide critical synergy with the NASA Atmosphere Observing System (AOS), which is currently in formulation and designed to address the Aerosols, Clouds, Convection, and Precipitation Designated Observables identified by the 2018 NASA Earth Science Decadal Survey. Here, we give an overview of the challenges in achieving cloud data record continuity across the existing multispectral LEO (MODIS, VIIRS) and GEO (ABI, AHI) imagers and the approaches the team has taken to-date to best achieve continuity. The relevant products are the MODIS standard cloud mask (MOD06/MYD06) and optical/microphysical property (MOD06/MYD06) products, the NASA CLDMSK and CLDPROP continuity cloud products (applied to MODIS Aqua and VIIRS on Suomi NPP/NOAA-20) that were first released to the public in November 2019, and research products run on AHI and ABI observations. Key challenges to data record continuity include:

1. 1. Fundamental differences in sensor specifications and/or orbits (spectral channels, spatial resolution/swath, viewing/solar geometries between LEO and GEO imagers);
2. 2. Differences in relative spectral radiometric calibration between the sensors, whether of the same design (MODIS Aqua v. MODIS Terra; VIIRS Suomi NPP v. VIIRS NOAA-20) or different (VIIRS v. ABI);
3. 3. The need for common geophysical algorithms across the sensor records to account for instrument differences (e.g., use of only a common/similar subset of available spectral channels) and incomplete retrieval information content (requiring common forward radiative models, ancillary data sources, inversion approaches);
4. 4. A flexible computational infrastructure that is designed to provide a robust and flexible science algorithm testing environment along with critical evaluation tools (including colocation and combined inter-sensor match files for on-orbit evaluation).

We also include examples of the impact of relative calibration discontinuities (item 2 above) and forward radiative models (item 3). Related poster submissions, titled Part II and Part III, provide more details regarding the Level-2/-3 continuity algorithms and product status (item 3, Meyer et al.) and computational infrastructure/tools (item 4, Holz et al.), respectively.