Project Overview

Atmospheric aerosol is one of the main drivers of climate changes. Importance of accurate global aerosol characterization for climate studies and air pollution monitoring is a well recognized problem (e.g., see IPCC AR5 by Boucher et al.2013). In addition to the traditional spectral Aerosol Optical Depth (AOD) such characterization should also include such extended aerosol information asaerosol size and type.

The global information about aerosol can be obtained from space-borne measurements only. Therefore, climate studies are becoming more and more relying on high quality aerosol characterization from space. At present time there are a number of different satellites on Earth orbit dedicated to aerosol studies. However, due to limited information content, the main aerosol products of the most of satellite missions is AOD while the accuracy of aerosol size and type retrieval from space-borne remote sensing still requires essential improvement.

Project Description

The problem of accurate extended aerosol characterization from satellite measurements is strongly affected by the complexity of reliable separation of atmosphere and surface signals. In addition to this, the information content of the measurements should be enough for aerosol characterization itself. 

Since the end of the POLDER/PARASOL mission in 2013, no single currently operating satellite satisfies completely the requirements for extended aerosol characterisation. At the same time, different satellites dedicated to atmospheric studies may overpass the same area on Earth surface during the same day but at different times or different relative positions. As a result, being properly collocated, such combined measurements can provide multi-angular,multi-temporal measurements in extended spectral range. More independent satellite measurements with different complementary capabilities are combined,the richer the information content of combined measurements becomes. Thetreatment of these data seems to be beyond the capacity of most of the existent traditional algorithms since the processing of multi-instrument observations is not commonly used. In contrast, such retrieval algorithms of the new generation like GRASP (Generalized Retrieval of Atmosphere and Surface Properties) were specifically designed for synergetic processing of diverse observations and can be highly useful for multi-instrument data processing (Dubovik et al. 2011,2021).

The GRASP multi-pixel retrieval concept has already been successfully applied to the observations of different single space-borne instruments: polar-orbiting like POLDER/PARASOL, MERIS, AATSR/ENVISAT, OLCI/Sentinel-3, TROPOMI/S-5p and geostationary, for example, Himawari, satellites. Moreover, the synergetic approaches were successfully approved on the synergy of MERIS and AATSR measurements (ESA CAWA-2 project) as well as on the synergy of the ground-based and satellite (AERONET+OLCI, AERONET+ TROPOMI/Sentinel-5p etc retrieval) measurements (ESA GROSAT project (Litvinov et al., 2021),

In the SYREMIS project we develop the prototyped synergetic retrieval with GRASP algorithm of combined measurements from diverse satellite instruments to bring the accuracy and scope of space-borne aerosol characterization to a new level required for climate studies and air-quality monitoring. In particular, these developments are expected to enhance the accuracy of traditional spectral AOD retrieval and allow the characterization of such aerosol properties as particle size, absorption, and chemical composition. Moreover, the proposed synergetic retrieval is expected to increase essentially the spatial and temporal coverage of the available aerosol product, which is absolutely required to identify aerosol sources and monitor aerosol transport. In this regard, the enhanced synergetic aerosol product is projected to have a significant impact on regional and global climate models (for example, CAMS and MERRA-2 global models). It is also expected to achieve the monitoring of natural or anthropogenic aerosol emissions which is crucial for air quality monitoring.

The synergetic retrieval in SYREMIS project is planned to be tested on the currently operating polar-orbiting (TROPOMI/Sentinel-5p, OLCI/Sentinel-3, SLSTR/Sentinel-3) and geostationary (Himawari) satellites. Moreover, the constellation of these multi-mission satellites is expected to be extended in future by the new generation of satellites like Sentinel-5, 3MI/EPS-SG, Sentinel-4, etc. 

The input for the synergetic retrieval may be diverse measurements from different satellites. Themain attention in this project will be played on the operating polar orbiting and geostationary satellites to enhance current state of aerosol characterization and to test the developments on the actual aerosol events. In particular,the multi-mission constellation in this project includes measurements from such polar-orbiting satellites like OLCI/Sentinel-3 A and B, TROPOMI/Sentinel-5p as well as the geostationary Himawari. On one hand such a constellation will extend the spectral range of the measurements. On another hand it will provide unprecedented spatial and temporal coverage which is crucial for global climate studies and air-quality monitoring. Moreover, the synergetic retrieval tested on this constellation can be easily adapted for future instruments like 3MI, Sentinel-5, Sentinel-4 etc.


The brief description of the selected satellites for the prototyped synergetic retrievalis summarized in Table 1.



OLCI/Sentinel-3A and OLCI/Sentinel-3B

– Polar-orbiting, global coverage

– One observation per grid point (4 by 4 pixels)

– Moderate spatial resolution

– Radiance measurements in VIS and NIR spectral range


– Polar-orbiting, global coverage

– Hyperspectral measurements in UV, VIS, NIR, SWIR spectral range


– Geostationary. Coverage area: Asia

– Every 10 min daily measurements

– Radiance measurements in VIS, NIR and SWIR spectral range

Table 1.Multi-mission constellation for prototyped synergetic retrieval



The synergetic multi-mission retrieval developed in SYREMIS is expected to enhance essentially the characterization of such aerosol produced from space-borne measurements as spectral AOD, SSA, and aerosol size characteristics etc. The proposed synergetic retrievals are expected both to improve accuracy of the retrievals and increase spatial and temporal coverage of the aerosol dataset. As a result, the enhanced synergetic aerosol product is expected to be of particularly high value for global climate studies and aerosol data assimilation in global aerosol models such as CAMS and MERRA-2. 

Project Consortium

GRASP Earth shorten from ‘Generalized Retrieval of Atmosphere and Surface Properties” is a company that was founded in February 2015 with the main goal of development of remote sensing algorithms and scientific methods for environment studies of atmosphere and surface of the Earth. The initial idea of GRASP has been developed by the efforts of CNRS and University of Lille. Then this base scientific concept has been realized in open-source GRASP-OPEN software adapted to diverse remote sensing applications. The main GRASP SAS activities cover a wide range of remote sensing topics: – Developments of algorithms for advanced atmosphere and surface characterization from passive and active ground based and space-borne remote sensing. – Scientific consulting in environmental studies. – Distribution and support of GRASP open source code. Since its creation, GRASP SAS has been involved in collaboration with world-wide environmental public organizations and private companies, universities and the largest space agencies (ESA, EUMETSAT, NASA, JAXA) with the goal to improve the scientific knowledge of the atmosphere and surface properties, which have an essential impact on Earth climate, and tightly interconnected with human activities. The GRASP code was developed for advanced aerosol and surface retrieval from remote sensing measurements. GRASP SAS is composed by a unique team with full understanding all aspects of the code: physical and mathematical basis, software optimization etc. GRASP team has leaded several projects to retrieve atmosphere and surface parameters from different satellite sensors (PARASOL, MERIS, Sentinel 3 and 4, 3MI).
Cloudflight Austria GmbH was founded as Catalysts GmbH in 2007 and has grown to over 400 employees distributed over offices in Austria, Germany, Romania and The Netherlands. We develop individual software solutions for industry, agencies, and the public sector focusing on Big Data and Machine Learning (batch processing of Tera- and Petabytes, process of data streams in real time or near real time), High Performance Computing (acceleration of algorithms), and Large-Scale Agile Projects (large-scale agile software projects „On Time & On Budget“). Cloudflight’s large international customer base includes Porsche/Volkswagen, Fraport, DB, Raiffeisen, EUMETSAT, and the European Space Agency. Our customers value our solid problem-solving competence so that they can grow further. Cooperation exists with several national and international universities, including the Technical Universities of Vienna and Graz, the LOA at the University of Lille, the Free University of Berlin, the Kindai University in Osaka, the Austrian Met-Office ZAMG, the Austrian Environmental Agency Umweltbundesamt, the German DLR, and NASA. As part of the consortium carrying out the “Sentinel-4 Level 2 Processor Component Development” project for ESA, Cloudflight is providing the prototype and operational processors for surface and aerosol optical depth for the Sentinel-4 mission using the GRASP algorithm. The processors will be integrated in EUMETSAT’s MTG Level 2 Processing Facility. In the frame of the ESA CAWA project, “Advanced clouds, aerosols and water vapor products for Sentinel-3” the MERIS/Envisat full mission and 6 months of OLCI/S3A were reprocessed using GRASP as precursor for improved Sentinel-3 L2 products. In the frame of the EUMETSAT study “Study on Optimization of the GRASP Algorithm for the 3MI L2 Aerosol Retrieval”, Cloudflight and GRASP SAS are preparing the integration of the GRASP algorithm into the EPS-SG ground segment as operational Level 2 processor for Aerosol and Surface Reflectance for the Multi-viewing Multi-channel Multi-polarization Imaging instrument, 3MI. 3MI can be considered an operational successor of the PARASOL mission, and will provide the best basis for future aerosol characterization from satellites. In the frame of the “GRASP Cloud project” tasked by the Beyond Europe Initiative of the Austrian Federal Ministry of Science, Research, and Economy, BMWFW, Cloudflight is developing a cloud service for data processing using the GRASP algorithm, together with GRASP SAS (France), EODC (Austria), NASA (JPL and GSFC, USA), Airphotons (USA), Kindai University (Japan), and RADI (China). The service offered by the GRASP Cloud is the processing of Satellite, Ground-Station, and in-situ observations for public agencies and private enterprises.