First images of climate satellite PACE released

Since its launch on 8 February 2024 from NASA's Kennedy Space Center in Florida, PACE has been carefully turned on to check that all instruments have withstood the violent shocks and exposure to space. That is now resulting in the first scientific images-First Light. "Eventually, a lot of these kinds of measurements will lead to a complete picture of aerosols in the atmosphere." So says Otto Hasekamp (SRON), principal investigator of SPEXone. "We are mapping how much of what kind of particulate matter there is. We will combine that information with climate models to investigate their contribution to global temperatures. Then we will know better to what extent particulate matter is masking warming caused by greenhouse gases."

"SPEXone works exactly as we conceived and designed it. The measurement instrument behaves just as it did during the last tests on the ground," says Marc Oort, systems architect at Airbus. "The careful design and meticulous assembly have proved their worth. SPEXone is ready for its important task."

The opening photo shows the world viewed from behind Polaroid sunglasses, compiled by SPEXone's hundreds of orbits around Earth. In the process, the instrument draws a 100-km-wide swath across the earth in the south-north direction like a broom. Different backgrounds such as sea and land polarize sunlight in their own way, making them look different. Land, for example, is often blue because only the scattered light in the air above it is polarised.

Figure 2 includes an orbit of SPEXone over Japan and Ethiopia. The rest of the picture was taken by the OCI instrument, also aboard PACE. Clouds are black because they do not polarize any colour. Aerosols polarize all colours of sunlight, giving themselves away. After analysing this polarisation data, the SPEXone team then maps the properties of the aerosols, as shown in Figure 3.

Figure 3 shows the properties of aerosols over Japan (Figure 3a) and Ethiopia (Figure 3b). Both consist mainly of fine particles. Indeed, both left panels show many red and yellow spots, while the middle panels are mostly blue. In the right panel, we see that the particulate matter over Ethiopia absorbs a lot of sunlight; it has the signature of smoke from biomass burning. Over Japan, we see a lot of fine dust around Tokyo, blown southwards by the wind. There, the right panel shows the signature of a mix of aerosol from industry and transport and, of course, particulate matter such as sea salt.

Jeroen Rietjens (SRON) was behind the controls in the control room at NASA's Goddard Space Flight Center when the first data came in. "When we gave the command to turn on SPEXone, it was a huge relief to see our instrument in good health. We were absolutely delighted when two weeks later we took the first camera images and managed to make particulate maps from them. That meant that all the links came together that we had all been working on for years."

Source: SRON

Opening photo: World map in polarised light, constructed from the 100-km-wide strips that SPEXone travels over Earth. Credit: SRON

Figure 2: SPEXone casts its 100-km wide field of view over Japan (top) and Ethiopia (bottom). The instrument measures the degree to which sunlight is polarised for different colours, from five different viewing angles. Credit: SRON

Figure 3: The conclusions from the polarisation measurements over Japan (top) and Ethiopia (bottom). The panels show the amount of fine particles, coarse particles and degree of absorption. Credit: SRON

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