Harmony-TIR: A Tandem EE10 Mission for Sentinel-1 for Better Understanding of Marine Boundary Layer Clouds and Their Interaction with the Ocean Surface: Initial ECSIM-DALES Simulations and Retrievals Using M2
MArine Boundary Layer (StCu MABL) clouds form vast dynamic areas of air-sea interaction around major cold currents off the coasts of major land masses, particularly in the eastern to central Pacific Ocean. They play a critical role in moderating the effects of global heating by producing large water droplet clouds which reflect most of the incoming solar radiation. The intimate nature of air-sea interaction is planned to be studied from the ESA Earth Explorer 10 mission candidate, named Harmony. Harmony consists of 2 identical spacecraft in tandem around Sentinel-1 with a 6/18hrs local equatorial crossing time. Their primary payload is a bistatic SAR to allow along-track interferometric retrievals of surface winds and waves. A second payload is proposed as a multi-angle thermal IR imager to obtain multi-angle images of cloud-fields and SST. This simultaneity will be exploited to gain a much better understanding of the role of air-sea interaction on the formation of MABL clouds and together with 10-15 minute GEO data can be employed to understand the diurnal evolution of these cloud systems and how in the longer-term they react to global heating of the sea surface.
The ESA Earthcare mission included the development of an Earthcare end-to-end Simulator (ECSIM) framework. This state-of-the-art end-to-end simulator creates all L1 products required for the official Earthcare L2 processors acceptance reviews to date. Due to its modular design and the separation between radiative transfer and instrument models, the system can be readily used for other missions like Harmony. The central idea behind the simulator lies in that there is a clear separation between the atmospheric model fields, the radiative transfer simulations and the instrumental effects. This means that for each location in the 3D-atmosphere there is a description of a particle size distribution for the different cloud and aerosol types combined with scattering libraries ranging from the UV to the Far-IR. Only after the radiative transfer calculations have been performed the instrument response functions is applied to calculate the signals as would have been seen by the satellite. The models in ECSIM include (a) 3D atmospheric scene definition; (b) orbital and instrumental models; (c) forward models from Monte Carlo to 1D DISORT. For ECSIM-HARMONY, the Dutch Atmospheric Large-Eddy Simulation (DALES), is employed [4] as a large-eddy simulation (LES) code designed for studies of the physics of the atmospheric boundary layer, including convective and stable boundary layers as well as cloudy boundary layers. The LES model results were subsequently put through the ECSIM-Harmony simulator to yield a set of radiance and Brightness Temperature (BT) fields as if viewed by an idealized Harmony TIR imaging system. Obviously the “cloud truth” was also available for these runs and these were used for subsequent “reality checks” on the retrieved dynamical quantities.
Two different simulations were employed with LES outputs, the first follows the early stages of a rapidly developing convective cloud system and consists only of liquid cloud droplets which have not yet grown to sizes where precipitation starts. The model was simulated on a 200x200m horizontal grid at a 40 m vertical resolution written out every 60 seconds. The second LES scene is based on the atmospheric conditions found during the EUREC4A campaign (February 6th, 2020), describing a low-level cumulus field with a relatively low cloud fraction. This LES scene is more complicated to retrieve CMV (Cloud Motion Vector) as many individual small clouds have comparable lifetimes with the overpass period and viewing angles of the two satellites. The horizontal model grid resolution is 100m with a 40m vertical grid spacing.
The retrieval framework and results for GEO-GEO stereo and SLSTR are described in a companion paper (Song et al., this workshop) is part of an open source project based on the operational system (M2, Multipoint Matcher) developed for the NASA MISR instrument onboard the EOS-Terra platform. The results from MISR-SMVs have been presented at the last four IWW workshops and were most recently published in. M2 results for both CMVs (both advective and vertical wind velocities) and cloud-top heights will be shown, and lessons learnt from the simulation-retrieval end-to-end system discussed.
