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EarthCARE's optical instruments poised to refine climate models

29 May 2024

Atmospheric lidar and multispectral imager among four on-board tools expected to improve understanding of cloud dynamics.

The European Space Agency (ESA) has confirmed the successful launch of “EarthCARE”, its joint venture with the Japan Aerospace Exploration Agency (JAXA) that is expected to provide a new level of insight into clouds and aerosols - and their influence on the planet’s climate.

Launched early May 29 aboard a Falcon 9 rocket from the Vandenberg Space Force Base in California, EarthCARE’s (short for Earth Cloud Aerosol and Radiation Explorer) payload includes four scientific instruments, leaning heavily on optics and photonics technology.

Those four instruments should soon start to send data that will offer an unprecedented view of the complex interactions between radiation, clouds, and aerosols - interactions that have a major influence on climate and weather, but which are relatively poorly understood currently.

Cloud uncertainty
Although it is known that clouds play an extremely important role in atmospheric heating and cooling, ESA says that they remain one of the biggest uncertainties in our understanding of how the atmosphere drives the climate system and how they will shape our future climate.

The agency explained prior to the EarthCARE launch: “While scientists know that clouds and aerosols play extremely important roles in both cooling and warming our atmosphere, there remains uncertainty when it comes to accounting for the exact influence they have on Earth’s energy balance and, given the ongoing climate crisis, if they will exert an overall cooling or warming effect in the future.

“For example, high, thin clouds tend to warm the atmosphere because a high proportion of energy from the sun can pass through and they are also efficient at trapping heat radiating from Earth’s surface.

“Low, thick clouds on the other hand, tend to have a cooling effect as they reflect a high proportion of the incoming sunlight back out to space.”

Aerosols also play a key role in Earth's climate system, partly by reflecting and absorbing incoming solar radiation and trapping outgoing radiation directly, but also by acting as “seeds” for cloud formation - the latter being their dominant influence, according to ESA.

Examples of aerosols include pollutants like sulfur dioxide and black carbon, which directly impact regional climate patterns where such pollutants are released, typically creating a cooling effect.

However, successful efforts to reduce harmful sulfur pollution also allow more solar radiation to reach Earth’s surface, changing cloud formation patterns and reducing that overall cooling effect.

Scientific instruments
EarthCARE’s four scientific instruments, which will each gather critical data on cloud and aerosol formation, include an ultraviolet atmospheric lidar, a multispectral imager, a cloud profiling radar, and a broadband radiometer.

ESA says that the cloud profiling radar will provide information on the vertical structure and internal dynamics of clouds, while the atmospheric lidar delivers profiles of aerosols and thin clouds as well as cloud-top information.

The multispectral imager is set to offer a wide-scene overview across visible and infrared wavelengths, and the broadband radiometer will measure reflected solar radiation and outgoing infrared radiation coming from Earth.

Following the launch, ESA’s Director of Earth Observation Programmes, Simonetta Cheli, said: “EarthCARE is the most complex of ESA’s research missions to date. Its development, and now launch, is thanks to close cooperation with our JAXA partners, who contributed the satellite’s cloud profiling radar instrument, and all of the space industry teams involved.

“The mission comes at a critical time when advancing our scientific knowledge is more important than ever to understand and act on climate change, and we very much look forward to receiving its first data.”

JAXA’s Project Manager for the cloud profiling radar, Eiichi Tomita, added: “Increasing the accuracy of global climate models by using EarthCARE data will allow us to better predict the future climate and therefore take necessary mitigation measures.

“JAXA provided the cloud profiling radar - the world’s first radar that can measure the velocity of upward and downward flow within clouds. We are expecting these EarthCARE data products to be remarkable.”

UV lidar
EarthCARE’s 500-kilogram atmospheric lidar is based around a frequency-tripled Nd:YAG laser operating at 355 nm and a 62 cm-diameter receiving telescope. The optical design is “bistatic”, meaning that separate optics are used for the transmitter and receiver elements.

It was designed to measure the vertical profile of aerosols and clouds, thus providing precise details about their distribution, altitude, thickness, optical properties, and aerosol type.

Developed by a team led by Airbus Defence and Space in France, the lidar provides a vertical resolution of 103 m from the ground up to 20 km altitude, and 500 m resolution at 20–40 km altitude.

Built by Surrey Satellite Technology, the multispectral imager captures a broad field of view to give context to the more precise profiling data, and will allow scientists to differentiate between various types of clouds, aerosols, and Earth’s surface.

It includes a 2D microbolometer array detector to collect images in three thermal channels, alongside a camera collecting images across four channels from the visible to shortwave infrared.

Each channel has its own dedicated optics and a linear array photodiode detector, and overall the instrument provides a 150 km swath width, with 500 m resolution.

Following the launch and successful rocket separation, ESA says that EarthCARE is now being controlled from its European Space Operations Centre in Darmstadt, Germany.

Controllers will spend the next few months carefully checking and calibrating the mission as part of the commissioning phase, prior to the start of scientific data collection.

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