Measurement at home
Measurement at home

An international post-launch calibration service for satellites

RadCalNet is a network of autonomous test sites to provide SI traceable reflectance values to satellites every 30 minutes

The need

Satellites can determine the health and state of the planet by measuring the spectral reflectance of sunlight off the Earth's surface. However, due to the harshness of the space environment, their radiometric performance changes with time. Regular checks against known values are essential to enable trust in the data they deliver.

The impact

The Committee on Earth Observation Satellites (CEOS) has recently established RadCalNet, a network of primarily desert-like sites which are equipped with autonomous instrumentation to allow top of the atmosphere reflectance values to be determined every 30 minutes. These are provided on an open access web portal to any satellite operator so they can check the consistency of their satellite's measurements.

NPL has played a central role in the development of RadCalNet, with responsibility for developing the guidelines on how to establish traceability and uncertainty for all the member sites. In addition, it has established and operates one of the member sites, Gobabeb in Namibia, on behalf of the European Space Agency.

RadCalNet not only supports the major space agencies, but is also providing a valuable resource for new commercial satellite operators and, in particular, constellations of microsats which are too small to have any on-board calibration capabilities.