Cluster of small satellites may improve climate projections

Small, shoebox-sized satellites, flying in formation around Earth, could estimate the planet's reflected energy with twice the accuracy of traditional satellites, and significantly improve climate projections, according to a new study led by an Indian-origin scientist.
If done right, such satellite swarms could also be cheaper to build, launch and maintain, researchers said.
Led by Sreeja Nag, a former graduate student at Massachusetts Institute of Technology (MIT), researchers simulated the performance of a single large, orbiting satellite with nine sensors, compared with a cluster of three to eight small, single-sensor satellites flying together around Earth.
They looked at how each satellite formation measures albedo, or the amount of light reflected from Earth - an indication of how much heat the planet reflects.

The team found that clusters of four or more small satellites were able to look at a single location on Earth from multiple angles, and measure that location's total reflectance with an error that is half that of single satellites in operation today.
Nag said such a correction in estimation error could significantly improve scientists' climate projections.

"Total outgoing radiation is actually one of the biggest uncertainties in climate change, because it is a complex function of where on Earth you are, what season it is, what time of day it is, and it's very difficult to ascertain how much heat leaves Earth," Nag said.

"If we can estimate the reflectance of different surface types, globally, frequently, and more accurately, which a cluster of satellites would let you do, then at least you've solved one part of the climate puzzle," she said.
"Earth does not reflect equally in all directions. If you don't get these multiple angles, you might under- or overestimate how much it's reflecting, if you have to extrapolate from just one direction," Nag said.
Today, satellites that measure Earth's albedo typically do so with multiple cameras, arranged on a single satellite.
For example, NASA's Multi-angle Imaging SpectroRadiometre (MISR) instrument on the Terra satellite houses nine cameras that take images of Earth from a fan-like arrangement of angles.

The drawback of this design is that the cameras have a limited view, as they are not designed to change angles and can only observe within a single plane, according to Nag.
Instead, the team proposes a cluster of small satellites that travel around Earth in a loose formation, close enough to each other to be able to image the same spot on the ground from their various vantage points.
"Over time, the cluster would cover the whole Earth, and you'd have a multiangular, 3D view of the entire planet from space, which has not been done before with multiple satellites," Nag said.

The study was published in the journal Acta Astronautica.