The atmospheric lidar ATLID, which is one of the four instruments on the EarthCARE satellite that launched in May, is now fully operational. This mission, a collaboration between the European Space Agency (ESA) and the Japanese Space Agency (JAXA), aims to improve the accuracy of measuring clouds, aerosols, and radiation like never before. Researchers from the Leibniz Institute for Tropospheric Research (TROPOS) are playing a crucial role by creating algorithms that analyze data from the instrument to derive information about aerosol and cloud layers. Additionally, a significant measurement campaign involving roughly 50 ground stations from the European ACTRIS network, coordinated by TROPOS in Leipzig, is enhancing the precision of this groundbreaking climate satellite.
Atmospheric lidar enhances the new climate satellite
Equipped with four advanced instruments — a cloud profiling radar, an atmospheric lidar, a broadband radiometer, and a multispectral imager — EarthCARE (Earth Cloud Aerosol and Radiation Explorer) will conduct various measurements simultaneously. These measurements are essential for understanding how clouds and aerosols reflect incoming solar energy back into space and how they capture thermal radiation emitted from the Earth. This understanding is crucial for assessing the impacts of climate change on the Earth’s energy balance and predicting the potential loss of cooling effects from clouds and aerosols in the future.
The EarthCARE satellite was placed in orbit on May 29, 2024. Within a month, the satellite successfully began sending back images from its cloud profiling radar, followed by images from the broadband radiometer, multispectral imager, and ultimately, the atmospheric lidar in August. This sophisticated instrument captures detailed vertical profiles of aerosols and clouds in various regions of the Earth’s atmosphere. Aerosols consist of tiny particles and droplets stemming from natural sources like dust and sea salt, as well as human activities such as industrial emissions and biomass burning. The lidar emits short bursts of ultraviolet light that are reflected back by atmospheric targets, and these signals are analyzed using a highly sensitive receiver. By measuring the travel time of the light, scientists can determine the distance, assess concentration through signal strength, and identify aerosol types based on polarization. This allows for the measurement of aerosol and cloud distribution and their characteristics, including height, thickness, and optical properties. The collaboration between the four instruments on the satellite is vital for grasping the role of aerosols and clouds in maintaining the Earth’s energy balance. A newly developed aerosol classification model, called “Hybrid End-to-End Aerosol Classification” (HETEAC), facilitates aerosol typing across multiple instruments. Notably, the ATLID atmospheric lidar is expected to greatly enhance air quality forecasts. Ulla Wandinger, who has worked on ATLID’s development for many years, expressed her excitement about the initial measurements: “The abundance of data and insight into atmospheric structures are incredibly impressive.” EarthCARE could significantly enhance our understanding of aerosols, clouds, their interactions, and the broader implications for climate research.
The first images captured in August illustrate the variety of aerosols and clouds present in the Earth’s atmosphere, such as a profile of Polar Stratospheric Clouds (PSC) over Antarctica, which are crucial in ozone hole formation, as well as Tropical Storm Debby over the Gulf of Mexico and smoke plumes from Canadian forest fires. Simonetta Cheli, ESA’s Director of Earth Observation Programmes, commented, “Following the initial images from EarthCARE’s other three instruments, we can now assess the effectiveness of the atmospheric lidar. The lidar’s profiles align with our expectations after it underwent routine calibration and decontamination. The insights we gain regarding the vertical distribution of clouds and aerosols will combine with those from the other instruments to deepen our understanding of Earth’s energy balance.”
Comprehensive measurement campaigns in the Atlantic and Europe
To ensure that the data from the new instruments are effectively utilized and interpreted, it is necessary to compare them with ground-based and airborne measurements across various scenarios. Consequently, multiple complex international measurement campaigns are currently taking place.
Until November, the German research aircraft HALO will conduct multiple flights under the EarthCARE path from locations in Cabo Verde, the Caribbean (Barbados), and Oberpfaffenhofen, Germany. This HALO-PERCUSION validation mission is spearheaded by the German Aerospace Center (DLR) in collaboration with the Max Planck Institute for Meteorology (MPI-M), with various partners, including the University of Leipzig. PERCUSION is just one of the several subprojects of the ORCESTRA (Organised Convection and EarthCare Studies over the Tropical Atlantic) research initiative coordinated by MPI-M. Another subproject, titled CLARINET (CLoud and Aerosol Remote sensing for EarThcare), involves TROPOS researchers validating EarthCARE data through the new ACTRIS remote sensing station at the Cabo Verde Atmospheric Observatory (CVAO) at the Ocean Science Centre Mindelo and comparing it with long-term measurements.
The ground stations associated with the European ACTRIS research network play a crucial role in calibrating the data obtained from the EarthCARE satellite. Over recent years, a variety of these stations have been established and expanded to analyze aerosols and clouds using remote sensing tools such as lidar and radar. Approximately 50 stations in both Europe and overseas are taking part in the atmo4ACTRIS measurement campaign. This extensive network is advantageous as EarthCARE passes over at least one of these stations nearly every day. Given the low-Earth orbit of the satellite, it revisits the same locations every 25 days, making it imperative to have multiple ground stations for effective calibration.
As part of the ATMO-ACCESS infrastructure project, simulated overflights were conducted for two months at the end of last year to rehearse and prepare for this intricate campaign. This preparatory phase was beneficial, as although the ACTRIS stations adhere to uniform standards, their validation processes can differ based on their specific backgrounds. “We are excited to start comparing the initial EarthCARE data with the in-situ measurements,” said Dr. Holger Baars from TROPOS, who is overseeing the campaign from Leipzig. Various partners, including ground stations in Leipzig and Melpitz operated by TROPOS, as well as those from the German Weather Service (DWD) in Hohenpeißenberg and Lindenberg, the University of Cologne (UoC) in cooperation with the Jülich Research Centre (FZJ), the Karlsruhe Institute of Technology (KIT), and the University of Leipzig, are also contributing to this effort. Furthermore, important observations from overseas are being provided by German partners, including the Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research (AWI), which is collaborating with UoC to gather data from Ny-Ã…lesund in the Arctic, while TROPOS is offering insights from three stations located in the Earth’s dust belt: Cabo Verde in the Atlantic, Limassol in Cyprus, and Dushanbe in Tajikistan.
