The atmospheric lidar ATLID has been successfully activated as the final instrument among the four aboard the EarthCARE satellite, which was launched in May. This collaborative mission by the European Space Agency (ESA) and Japan’s Space Agency (JAXA) aims to improve the precision of cloud, aerosol, and radiation measurements. Researchers from the Leibniz Institute for Tropospheric Research (TROPOS) are playing a key role by creating algorithms that analyze the aerosol and cloud layering based on data captured by the device. Additionally, a comprehensive measurement initiative that includes around 50 ground stations from the European ACTRIS network—managed by TROPOS in Leipzig—is further enhancing the satellite’s accuracy.
Atmospheric lidar enhances the new climate satellite
EarthCARE (Earth Cloud Aerosol and Radiation Explorer) is outfitted with four cutting-edge instruments: a cloud profiling radar, an atmospheric lidar, a broadband radiometer, and a multispectral imager. This configuration allows EarthCARE to carry out various measurements at once, aiding in a better understanding of how clouds and aerosols reflect solar energy away from Earth and how they capture the thermal radiation released by the planet. This data is vital for comprehending the impact of climate change on Earth’s energy dynamics and for forecasting the potential decline in cooling effects from clouds and aerosols in the future.
Launched into Earth’s orbit on May 29, 2024, the satellite provided its initial cloud profiling radar images just a month later. This was followed by images from the broadband radiometer, the multispectral imager, and finally, the atmospheric lidar in August. This advanced instrument captures detailed vertical profiles of aerosols and clouds over various Earth locations. Aerosols are minuscule particles that originate from natural sources like dust and sea salt, as well as from human activities such as industrial processes and burning wood. The laser emits rapid bursts of ultraviolet light, which get reflected by atmospheric objects before being analyzed by a sensitive receiver. The distance is calculated based on the time taken for the light to return, while the concentration is gauged from the signal strength and the type of aerosol is identified by its polarization. This technology enables accurate measurements of aerosol and cloud characteristics, including their altitude, thickness, and optical and physical attributes. The collaboration with the other three satellite instruments is essential for comprehending how aerosols and clouds influence Earth’s energy balance. A newly developed aerosol classification model called “Hybrid End-to-End Aerosol Classification” (HETEAC) has been specifically designed to ensure effective aerosol typing across the different instruments. The ATLID atmospheric lidar will also contribute significantly to enhancing air quality predictions. Ulla Wandinger, a long-time contributor to the ATLID project, expressed her excitement about the first data collected, noting, “The extensive data and detailed atmospheric insights are truly remarkable.” EarthCARE holds the promise of significantly advancing our understanding of aerosols, clouds, and their interactions, impacting climate research immensely.
The initial images released in August showcase the variety of aerosols and clouds present in Earth’s atmosphere, such as a profile of Polar Stratospheric Clouds (PSC) above Antarctica, which are crucial to ozone hole formation, as well as Tropical Storm Debby over the Gulf of Mexico, and smoke plumes from wildfires in Canada. Simonetta Cheli, ESA’s Director of Earth Observation Programmes, remarked, “With the release of the first images from EarthCARE’s other three instruments, it’s exciting to finally see how effectively the atmospheric lidar is performing. The profiles obtained from it match our expectations closely, following the necessary decontamination and calibration processes. The atmospheric lidar provides us with novel insights into the vertical distribution of clouds and aerosols, and in conjunction with the other instruments, it puts us on the path toward a deeper scientific understanding of Earth’s energy balance.”
Comprehensive measurement efforts in the Atlantic and Europe
To optimize the use of data from the new instruments, it is critical to validate these findings with ground-based and airborne measurements across various scenarios. Consequently, a series of intricate international measurement campaigns are currently in progress.
The German research aircraft HALO will conduct flights beneath the EarthCARE satellite’s path several times from locations in Cabo Verde in the Atlantic, Barbados in the Caribbean, and Oberpfaffenhofen in Germany until November. This HALO-PERCUSION validation mission is being led by the German Aerospace Center (DLR) in collaboration with the Max Planck Institute for Meteorology (MPI-M), with participation from several partners, including the University of Leipzig. PERCUSION is one of multiple subprojects within the ORCESTRA (Organised Convection and EarthCare Studies over the Tropical Atlantic) research initiative coordinated by MPI-M. Another subproject, CLARINET (CLoud and Aerosol Remote sensing for EarThcare), involves TROPOS researchers utilizing the newly established ACTRIS remote sensing station at the Cabo Verde Atmospheric Observatory (CVAO) to validate EarthCARE data in the tropical Atlantic and compare it with long-standing measurements.
The ground stations within the European research infrastructure ACTRIS play a vital role in calibrating the EarthCARE satellite’s data. These stations, developed and expanded in recent years, analyze aerosol particles and clouds using remote sensing tools like lidar and radar. Approximately 50 stations across Europe and beyond are participating in the atmo4ACTRIS measurement campaign. This dense network allows the unique advantage of EarthCARE passing over at least one of the stations nearly every day, as the satellite orbits Earth’s low altitude and returns to the same area only every 25 days. Thus, a single ground station cannot suffice for accurate calibration.
“As part of the ATMO-ACCESS infrastructure initiative, we practiced the measurement campaign for two months last year using simulated overflights, which significantly helped prepare us for this complex task. Although all ACTRIS stations adhere to the same standards, they differ in certain aspects regarding the validation of satellite data. We are eagerly anticipating the comparison of the first EarthCARE data against our ground measurements,” shared Dr. Holger Baars of TROPOS, who is coordinating the campaign from Leipzig. In addition to the TROPOS stations in Leipzig and Melpitz, the German Weather Service (DWD) stations in Hohenpeißenberg and Lindenberg, the University of Cologne (UoC) along with the Jülich Research Centre (FZJ), the Karlsruhe Institute of Technology (KIT), and the University of Leipzig will participate. Moreover, significant contributions from German partners include data from the Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research (AWI), which is providing observations from Ny-Ã…lesund in the Arctic, in partnership with the UoC, while TROPOS is contributing data from three locations in the Earth’s dust belt: Cabo Verde in the Atlantic, Limassol in Cyprus, and Dushanbe in Tajikistan.
