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EarthCARE Satellite’s Atmospheric Lidar Begins Operations

The atmospheric lidar ATLID, the final instrument of the EarthCARE satellite that launched in May, is now fully operational. This collaborative initiative by the European Space Agency (ESA) and the Japan Aerospace Exploration Agency (JAXA) aims to enhance the measurement accuracy of clouds, aerosols, and radiation. Researchers from the Leibniz Institute for Tropospheric Research (TROPOS) play a significant role in this mission by creating algorithms that analyze aerosol and cloud distributions based on data collected from ATLID. Furthermore, a wide-ranging measurement campaign involving approximately 50 ground stations from the European ACTRIS network, organized by TROPOS in Leipzig, is bolstering the reliability of the new climate satellite.

Atmospheric Lidar Completes EarthCARE’s Instrumentation

EarthCARE, which stands for Earth Cloud Aerosol and Radiation Explorer, is outfitted with four advanced instruments: a cloud profiling radar, an atmospheric lidar, a broadband radiometer, and a multispectral imager. These instruments will facilitate simultaneous data collection, enabling a deeper understanding of how clouds and aerosols influence solar energy reflection and thermal radiation retention. Understanding these dynamics is crucial for assessing climate change impacts on the Earth’s energy balance and predicting the duration of current cooling effects from clouds and aerosols.

Launched on May 29, 2024, EarthCARE transmitted its first images from the cloud profiling radar just a month after its launch. This was shortly followed by images from the broadband radiometer, the multispectral imager, and finally, the atmospheric lidar in August. ATLID provides precise vertical profiles of aerosols and cloud formations across diverse Earth regions. Aerosols, tiny particles originating from both natural phenomena—such as dust and sea spray—and human activities like industrial processes and combustion, are analyzed through the lidar’s short-pulse ultraviolet laser. This laser allows for measurement of distance based on light transit time, concentration from signal intensity, and aerosol type through polarization analysis. Consequently, ATLID can determine the distribution and characteristics of aerosols and clouds, including aspects like elevation, thickness, and optical traits. The integration of data from ATLID with the satellite’s other instruments is essential for a comprehensive understanding of how aerosols and clouds contribute to the Earth’s energy balance. Additionally, a new aerosol classification model, termed “Hybrid End-to-End Aerosol Classification” (HETEAC), has been developed to enhance accuracy in aerosol identification across the instruments. Ulla Wandinger, deeply involved in ATLID’s development, expressed her excitement over the initial data, noting the impressive breadth of information and detailed atmospheric insights it provides. The potential of EarthCARE to advance research on aerosols, clouds, and their complex interactions is considerable.

The first lidar images from August showcased the variety of aerosols and clouds within the Earth’s atmosphere. Notable observations included a profile of Polar Stratospheric Clouds (PSC) above Antarctica, which are crucial in ozone layer depletion, along with images from Tropical Storm Debby over the Gulf of Mexico and smoke plumes from Canadian forest fires. Simonetta Cheli, ESA’s Director of Earth Observation Programmes, remarked on the successful performance of the atmospheric lidar, which met expectations following routine decontamination and calibration processes. This lidar’s capacity for providing deep insights into the vertical distribution of aerosols and clouds, especially when combined with other instruments, positions scientists to gain a more nuanced understanding of the Earth’s energy dynamics.

International Measurement Campaigns Underway

To maximize the utility and interpretation of the newly gathered data, comparative evaluation with ground and aerial measurements is essential. In this context, several complex international measurement campaigns are currently in progress.

German research aircraft HALO will operate multiple flights beneath the EarthCARE’s orbital path, originating from locations such as Cabo Verde in the Atlantic, Barbados in the Caribbean, and Oberpfaffenhofen in Germany until November. The HALO-PERCUSION validation mission is spearheaded by the German Aerospace Center (DLR) in collaboration with the Max Planck Institute for Meteorology (MPI-M). Additional partners, including the University of Leipzig, are involved in this endeavor. PERCUSION is a segment of the broader ORCESTRA (Organised Convection and EarthCare Studies over the Tropical Atlantic) research initiative, coordinated by MPI-M. Another project, CLARINET (CLoud and Aerosol Remote sensing for EarThcare), has TROPOS researchers utilizing the new ACTRIS atmospheric remote sensing station at the Cabo Verde Atmospheric Observatory (CVAO) to validate EarthCARE’s data in the tropical Atlantic alongside long-term data comparisons.

Ground stations within the ACTRIS framework play a pivotal role in calibrating EarthCARE’s satellite data. Established and expanded in recent years, these stations are equipped to analyze aerosol concentrations and cloud characteristics using various remote sensing technologies including lidar and radar. Approximately 50 stations across Europe and beyond are actively participating in the atmo4ACTRIS measurement campaign. This tightly-knit network is advantageous, as EarthCARE surveys at least one of these stations nearly every day, given its low-Earth orbit, which revisits the same location every 25 days. Therefore, no single ground station provides sufficient calibration on its own.

In preparation for this complex scientific task, teams undertook a simulated overflight exercise as part of the ATMO-ACCESS infrastructure project, rehearsing the measurement campaign for two months at the end of the previous year. Dr. Holger Baars from TROPOS, overseeing the campaign, noted the insightful contributions from each ACTRIS station to the validation of satellite data despite operational differences. Alongside TROPOS stations in Leipzig and Melpitz, additional collaboration involves the German Weather Service (DWD) sites in Hohenpeißenberg and Lindenberg, as well as contributions from the University of Cologne in conjunction with the Jülich Research Centre (FZJ) and the Karlsruhe Institute of Technology (KIT). Insights from various international partners are also enriching the project, including significant data from the Alfred Wegener Institute collaborating with the University of Cologne to provide essential observations from Ny-Ålesund in the Arctic, along with data collection in multiple locations within the Earth’s dust belt, such as Cabo Verde, Limassol in Cyprus, and Dushanbe in Tajikistan.

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