Conference Agenda

In August 2018, ESA’s Earth Explorer mission Aeolus has been successfully launched to space. Since then Aeolus has been demonstrating its capability to accurately measure atmospheric wind profiles from the ground to the lower stratosphere on a global scale deploying the first ever satellite borne wind lidar system ALADIN (Atmospheric Laser Doppler Instrument).

In order to identify and correct the systematic error sources, guarantee and enhance the performance of ALADIN and the data quality of the wind products, several calibration and validation campaigns were implemented. In the aspect of ALADIN calibration, the ALADIN laser frequency stability and its impact on wind measurement was assessed and the correction of wind bias for ALADIN using telescope temperatures was conducted. Shortly after the launch of Aeolus, co-located airborne wind lidar observations, which employed a prototype of the satellite instrument – the ALADIN (Atmospheric LAser Doppler INstrument) Airborne Demonstrator (A2D), were performed in central Europe, meanwhile ground-based coherent Doppler wind lidars (CDLs) net was established over China, to verify the wind observations from Aeolus.

Aeolus has the capability to measure wind profiles and aerosol optical properties profiles synchronously, which provides the possibility for studying the wind-driven evolution of aerosol. Combining the measurements of ALADIN/Aeolus and the data from other spaceborne sensors, together with NWP models, wind-driven dust aerosol transport, smoke aerosol transport and marine aerosol production are analyzed, respectively.

Based on the observation of ALADIN, combined with the data of CALIOP, AIRS, ECMWF and HYSPLIT, a long-term large-scale Saharan dust transport event which occurred between 14 and 27 June 2020 is tracked and the possibility of calculating the dust mass advection is explored. The dust event's emission phase, development phase, transport phase, descent phase and deposition phase on 15, 16, 19, 24 and 27 June are captured by the quasi-synchronization observations of ALADIN and CALIOP, which is verified with the AIRS Dust Score Index data and the HYSPLIT trajectories. The dust mass advection of each transport phase is calculated.

Based on the observation of ALADIN, combined with the data of CALIOP, MODIS, MERRA-2 and HYSPLIT, a long-term smoke aerosol transport event which occurred during 11 to 21 September 2020 from western America to northern Europe is observed. The smoke layers of different transport phases are identified and analyzed. A new strategy is proposed for spaceborne lidars to estimate smoke mass concentration based on extinction coefficients at 355 nm and column mass concentrations from MERRA-2. A smoke transport tunnel from western America to northern Europe is found based on the wind vector profiles from Aeolus. The smoke transport fluxes of each cross-section are calculated to quantitatively evaluate the transport intensities.

Based on the observation of ALADIN and CALIOP, combined with the data from ECMWF, the correlation between marine aerosol optical properties and wind speeds over remote oceans is investigated. Three remote ocean areas are selected. Pure marine aerosol optical properties at 355 nm are derived from ALADIN. The relationship between marine aerosol optical properties and wind speeds are analyzed within and above the marine atmospheric boundary layer, revealing the effect of wind speed on marine aerosol over the remote ocean.

Global observations of column carbon dioxide concentrations and aerosol optical properties profiles are important for climate study and environment monitoring which is why China decided to implement the lidar mission ACDL (Aerosol and Carbon dioxide Detection Lidar) to measure CO2 and aerosol from space – has been launched to space successfully on 16 April 2022. The commissioning phase of ACDL is scheduled to be 6 months, during which the calibration and validation campaigns are implemented and the retrieval algorithms of column carbon dioxide concentration and aerosol optical properties profiles are improved. It is expected that with the calibrations and validations of ACDL and the updates of retrieval algorithms, the products of ACDL will be accurate and robust for science applications.

Remote sensing of ocean color over coastal waters is challenging and these difficulties can be placed in 3 categories: i) adverse atmospheric conditions associated with the presence of thin clouds or thick aerosol plumes (sometimes biomass burning), ii) challenging environments found over or around the water target (boundary conditions); iii) extreme conditions associated with the water content in optically active constituents (high concentrations of sediments). Evaluation and improvements of the estimation of bio-optical and biogeochemical parameters is an indispensable task for accurately monitoring the dynamics and the quality of coastal waters through the use of ocean color remote sensing. Especially, with the improvement of sensor ability and the advent of novel retrieval algorithms/models, ocean color is playing a more and more important role in understanding the utilization, the protection and the management of coastal environments. Ocean color data can thus provide biogeochemical data with known uncertainty, which is of great importance for quantitatively characterizing variation of key elements in coastal ecosystem and is required for input in modelling. Sentinel 3A/3B is new generation ocean color missions in Copernicus program in Europe, while HY-1C/1D is the first operational ocean color satellites in China. Their optical sensors (OLCI for Sentinel 3 and COCTS for HY-1) provide invaluable knowledge of ocean ecosystems due to their large swath and frequent coverage.

This project was undertaken by ocean color scientists, researchers, engineers and young students from both China and France. We aimed at tackling above-mentioned issues over European (mainly French) and Chinese coastal waters. The main scientific objectives concern the monitoring of the quality of the French and Chinese coastal waters using OLCI and COCTS/CZI space-borne sensors. The project is divided into two tasks: (i) Characterization of uncertainty of OLCI and COCTS/CZI ocean color products in coastal waters; (ii) Development of novel regional EO datasets in coastal waters. The former focused on evaluating the atmospheric correction and bio-optical algorithms of OLCI and COCTS/CZI in areas of interest using in-situ measurements collected by team members and those from world-wide open source, while the latter was to develop regional bio-optical algorithms for the Chinese/French coastal waters according to specific spectral configuration of COCTS and OLCI.

Since the beginning of the project, the team have collected OLCI/Sentinel-3 and COCTS/Haiyang-1 operational products delivered by the National Satellite Ocean Application Service (NSOAS), China and EUMETSAT EO Portal, European Union, respectively. The data covers regions of interest (ROI) in China and Europe, such as coastal waters in the Yellow Sea and the East China Sea in China, and in the Adriatic Sea and the Black Sea in Europe, etc. Results of validation and utilization of EO data in various ROIs will be presented.

Firstly, validation results of OLCI and COCTS L2 products over different coastal waters across Europe and China will be presented. In this report, reference data including both aerosol and sea-water reflectance are acquired by an automatic photometer (CE318-TV12-OC, also called SeaPRISM) manufactured by CIMEL corporation (France). It measures the sun, sky and sea surface periodically, from which aerosol optical thickness (AOT) and Remote-sensing reflectance (Rrs) can be derived. This instrument has already been operationally deployed in AERONET-OC network. Various CE318 station are selected in coastal waters around Europe and China. They are all deployed on offshore platforms where sea water demonstrates different optical signatures. Community popular spatial/temporal match-up protocols were used. With temporal coverage spanning between January 2020 and December 2023, validation results show that (i) OLCIs onboard Sentinel A/B tend to over-estimate AOT in both European and Chinese waters, even though general trend prevails between OC data and in-situ data. Such over-estimation is more notable in Europe. (ii) Irrespective of water types, AOT from COCTSs show no obvious over-/under-estimation in general, but demonstrates more significant uncertainty (i.e., big dispersion) than that of OLCIs. (iii) Rrs from OLCIs agrees very well with in-situ measurements in most visible-infrared bands. However, COCTSs tend to under-estimate Rrs across various waters. For reference, NASA operational L2 OC products (e.g., MODIS/AQUA) were also validated using same match-up protocol as of COCTS and OLCI.

Moreover, we finished consistency check between either OLCI or COCTS and NASA operational L2 OC products (e.g., MODIS/AQUA) in normally one by one degree box areas nearly centered with CE318 stations. Consistency has also been checked between OLCI and COCTS.

Then, we finished spatial-temporal analysis of the variability of the concentration of chlorophyll-a concentration is analyzed for the OLCI sensor over Chinese and European coastal waters. This analysis is part of the PhD thesis of a young scientist. The trend, seasonal and intra-seasonal patterns are analyzed between 2016 and 2023.

Lastly, we will also summarize young scientist training.