CT For Clouds: Ten Israeli Micro-Satellites Will Look Inside the Smallest Clouds

The Lord is slow to anger and great in power, and the Lord will by no means clear the guilty. His way is in whirlwind and storm, and the clouds are the dust of his feet. Nahum 1:3 (The Israel Bible™)

Computerized tomography (CT) scanners have been used widely for some two decades to provide cross-sectional images of organs and tissues inside the human body for diagnosis of medical problems and to treat disease.

Mathematical algorithms (sets of rules to be followed in calculations) are used to reconstruct the images from projection data obtained at many different angles around the patient. The better the algorithm, the more accurate the image.

Now, an Israeli-German mission is preparing to launch a formation of 10 tiny satellites – each the size of a shoebox and weighing three kilograms – that will use medically inspired CT algorithms to better understand clouds and their role in climate. The project, called CloudCT, has already won a €14 million European Research Council (ERC) Synergy program award – the maximum sum that can be allotted from this program.

The scientists are now building their teams and starting to work out details of the project. They plan to spend much time designing and testing many aspects of CloudCT prior to launch.

The satellites are due, in a few years, to enter orbit and begin filling in some gaping holes in our understanding of clouds and their role in climate. Inspired by medical CT, the mission scientists are creating a system that will reveal detailed images of the clouds’ external and internal 3D structures and properties.

By probing small cloud fields that are generally missed by today’s remote- sensing technologies, the mission aims to resolve some major uncertainties that limit current atmospheric modelling and climate prediction. 

The tiny satellites, to be carried by a spacecraft called Genesis, are designed to fly in formation continuously over hundreds of kilometers in space to derive 3D information from the images. These include making estimates of rain-droplet size and their concentration within the clouds.

Three investigators lead this unique interdisciplinary project – two Israelis and a German. Prof. Yoav Schechner of the Viterbi Faculty of Electrical Engineering at the Technion-Israel Institute of Technology in Haifa is an expert in computer vision and computed tomography. Prof. Ilan Koren is an expert in cloud and rain physics in the earth and planetary sciences department of the Weizmann Institute of Science in Rehovot, Israel. Prof. Klaus Schilling of the Center for Telematics (in Würzburg) is a leader in the field of small satellite formation technology.

Clouds have a key role in Earth’s energy balance and its water cycle; even small errors in assessing clouds’ properties can lead to major inaccuracies in climate predictions. “Satellites study large cloud structures, but lack the resolution to observe small clouds,” explained Koren. “Although they are small, such clouds temper the climate, on the one hand, and on the other, they may be very sensitive to climate change. That is why there is a critical need to measure these small clouds properly — to understand their nature and their interplay with changing environmental conditions. CloudCT can pave the way to this understanding,” he continued.

The idea for probing these clouds from space was motivated by the technology of 3D medical imaging. “We are using human health as guidance for the planet’s health,” Schechner added. In analogy to the better-known medical CT, images in CloudCT will be taken simultaneously from many directions around and above the clouds. This feat will be made possible by the networked self-organizing formation of multiple, affordable, very small and very agile satellites. However, “contrary to isolated clinic laboratory settings, the Earth is irradiated by illumination from the sun, which cannot be moved around or turned on and off. Our image-analysis algorithms must account for this reality and rely on light scattering, which challenges our task,” said Schechner.

The precision control required of the multi-satellite system to conduct this complex imaging raises challenges in miniaturization, as well as in coordination and autonomous reaction capabilities. Schilling expresses his excitement about the prospects of the CloudCT project: “The distributed networked satellite systems we are developing for CloudCT are an example of the ways that innovative software compensates for the deficits brought about by miniaturization. This enables a self-organizing system to be implemented efficiently by such ultra-small satellites and for novel approaches to observation to help achieve scientific advances.”

Their testing is being aided by a precursor mission of three satellites, called TOM (Telematics Earth Observation Mission) as well as a high- performance dynamics simulator in Würzburg, said Schilling. “This project will give us the opportunity to see and measure clouds as never before,” said Koren. 

“We are very pleased that the ERC selected the CloudCT project,” concluded Schechner. “We can already say that CloudCT is pioneering new concepts of Earth observation and the development of sophisticated computational imaging algorithms.”