Many Earth Observation satellites use the Moon as an added component to ensure reliable, good quality environmental data and satellite images.
While the surface of the Moon is always changing, the face of the Moon has stayed the same for millions of years. This makes the light reflecting from the lunar surface an ideal calibration source for optical Earth observation instruments and for satellite images.
A European Space Agency (ESA) led project now has plans to utilise the planet even more.
According to ESA, an instrument has been placed on the slopes of Mount Teide, Tenerife, Spain, above the majority of clouds and airborne dust. It is designed to measure nightly variations in moonlight in order to improve the accuracy of lunar calibration efforts in the future.
Marc Bouvet, overseeing the project for ESA, said: “Space agencies across the globe use the Moon to assess and monitor the calibration of optical Earth observation instruments.
“These instruments are carefully calibrated before launch, but in space their performance can gradually drift, due to radiation or lens contamination, for instance, or mechanical changes.”
Using calibration devices for missions
Some missions include internal calibration devices while others use relatively unchanging terrestrial features such as featureless stretches of desert, oceans, or salt flats, modelling the radiation coming from these targets. However, any location on Earth may still vary over time.
Bouvet said: “We need to be sure that changes in the light received from Earth represent genuine changes on the ground versus changes in the instrument. Accordingly, we need calibration targets – representing an unchanging, stable light source – to pinpoint any performance drift in space instrument measurements.”
The instrument installed on Mount Teide is a solar photometer, similar to those used by a global network, measuring particles in the atmosphere. This one, however, has been specially adapted to work during the night instead of the day, measuring moonlight instead.
The project, backed through ESA’s Basic Activities, is being undertaken by a consortium incorporating the UK’s National Physical Laboratory, as well as Spain’s Valladolid University and Belgium’s VITO, the Flemish Institute for Technological Research.