Other algorithm studies
Read our other algorithm studies for current, future and multi-missions.
30 January 2023
20 January 2020
Aerosol composition and associated spatial distribution are key parameters for the improvement of the air quality and climate products. Therefore, EUMETSAT will increase the number of satellite aerosol parameters provided operationally, which are driven by the 3MI instrument. The Multi-Viewing Multi-Channel Multi-Polarisation Imaging (3MI) instrument is planned to fly on the Metop-SG A satellites, as part of the EUMETSAT Polar System-Second Generation (EPS-SG) mission, in the timeframe beyond 2022. It is a radiometer dedicated to aerosol and cloud characterisation for climate monitoring, atmospheric composition, air quality and numerical weather prediction.
This polarimetric instrument is a heritage of the POLDER instruments, with improved capabilities. The spectral range (12 channels) was extended from the visible-near-infrared (410 to 910 nm) to the shortwave-infrared domain (up to 2200 nm). The spatial resolution (4 km at nadir) and the swath (2200 × 2200 km2) were also improved compared to previous POLDER instruments. As POLDER, 3MI will provide multi-polarisation (-60°, 0°, and +60°), and multi-angular (10 to 14 views) images of the Earth top of atmosphere outgoing radiance.
The level 1 products available to the users will be the geolocated Stokes vectors on the native geometry (Level 1B) and the geoprojected multi-directional and spectral Stokes vectors. Level-2 products will provide geophysical and microphysical parameters for aerosols and clouds. The aerosol retrieval for the 3MI operational product will use the GRASP algorithm. The retrieval provides extended set of aerosol and reflectance surface parameters.
GRASP (Generalized Retrieval of Aerosol and Surface Properties) is a highly accurate aerosol retrieval algorithm that processes properties of aerosol and land surface reflectance. It infers nearly 50 aerosol and surface parameters, including particle size distribution, the spectral index of refraction, and the degree of sphericity and absorption. The algorithm is designed for the enhanced characterisation of aerosol properties from spectral, multi-angular polarimetric remote sensing observations. GRASP works under different conditions, including bright surfaces such as deserts, where the reflectance overwhelms the signal of aerosols. GRASP has demonstrated a strong reliability for aerosol retrieval and characterisation on the PARASOL mission.
The aim of this study is to assess the use (e.g. computationally expensive elements, sensitivity studies) of the GRASP algorithm for future optimisation, in order to update the day 1 3MI Level 2 aerosol product generation which has a non-sufficient level of performances. This is an important and urgent step, as the PDAP development (i.e. the ground segment) is ongoing and preparation of the new 3MI processing needs timely definition.
This study has assessed GRASP in three distinctive regards, it has:
All three assessments have a positive outcome, and therefore, no major blocker is to be expected for an operational integration of GRASP for EPS-SG/3MI from either of these three engineering perspectives.
To address these questions, six different settings of GRASP, described in table in Figure 1, have been tested and compared to the nominal performance of GRASP, as described at the GRASP-Open webpage. From the overall perspective, specifically the GRASP setup with fixed surface information or an initial guess for it — which can, and should be, taken from GRASP itself — show a good performance fitting within the NRT requirements, and the least amount of documentation effort.
Based on the efforts done within the project and described above, the following conclusions are drawn:
In terms of quality:
In terms of compute resources: