The NASA satellite PACE, which is to study the atmosphere and the oceans, has had its first measuring instrument since the end of last week: the Dutch SPEXone.

If you are allowed to participate in a satellite, it does require some patience. As early as March 2021, the SPEXone instrument, built by SRON and Airbus Nederland with the help of TNO, was delivered to the Goddard Space Flight Center in the US. But only in the past few weeks has SPEXone finally mounted in its intended place: the NASA satellite PACE†

PACE is to determine the color of the oceans from January 2024. But the satellite will also measure small particles in the atmosphere – thanks to the SPEXone instrument and its American counterpart HARP2. And that can provide crucial information for climate models.

Important milestone

During the assembly of SPEXone, the instrument was connected for the first time to the power supply of the satellite itself, explains SRON engineer Alexander Eigenraam, who has just returned from the US. “That was an important milestone.”

SPEXone is mounted on PACE

American and Dutch technicians mount the SPEXone instrument on the satellite PACE. At the back SRON engineer Alexander Eigenraam.

There were no major setbacks. “The housing of one plug was too large, so two plugs couldn’t fit next to each other,” Eigenraam recalls. “And there were some minor software issues.” But in the end the instrument was neatly in place last Thursday.

Floating micro-organisms

Much remains to be done in the year and a half to PACE’s planned launch. “SPEXone is only the first instrument mounted on the satellite,” says Eigenraam. Then two more follow: the Hyper-Angular Rainbow Polarimeter #2 (HARP2) and the Ocean Color Instrument (OCIA†

OCI is the main tool that comes with PACE. As the name implies, it is supposed to measure the color of the ocean water. That color then tells scientists more about the phytoplankton: micro-organisms floating around in the water that get their energy from sunlight. “Phytoplankton are the source of half of the oxygen in the atmosphere,” says Eigenraam. “That’s why it’s super important to know how it stands and where it’s headed.”

Uncertain effect on the climate

Meanwhile, SPEXone and HARP2 focus on so-called aerosols: small particles that float around in the air. These have an important influence on the climate: they can reflect sunlight, which is therefore sent back into space and therefore does not contribute to global warming. Furthermore, aerosols help form clouds – which in turn can also reflect sunlight. In addition, aerosols can absorb sunlight, thereby exacerbating climate change.

“SPEXone has to collect sunlight that aerosols have reflected,” Eigenraam explains. “On the basis of that light, we can determine what kind of particles are involved, how large they are, and what their density is. This will make climate models more reliable. Because at the moment the effect of aerosols on the climate is still very uncertain.”

Variant for European mission

In addition, SPEXone and HARP2 help with PACE’s main mission: determining the color of the ocean. There are also aerosols and clouds between the satellite and the ocean, which can influence the measurements of the OCI instrument. Thanks to the measurements of SPEXone and HARP2, OCI can take these disturbing effects into account when making its own observations.

Incidentally, it may not stop at SPEXone. In Europe, work is underway on the CO2M climate satellite, which should measure the concentrations of carbon dioxide in the atmosphere. And a variant of SPEXone, called SPEXone250, is a candidate to join that mission. Because aerosols are also a phenomenon to keep an eye on when determining carbon dioxide concentrations.