The MHS instrument is a compact five-channel self-calibrating microwave rotating radiometer weighing around 63 kg designed to scan through the atmosphere to measure upwelling microwave radiation from the Earth at specific frequency bands. Occupying a 0.8-metre cube, it is positioned on the nadir facing (Earth facing) side of the MetOp satellite and is designed to scan perpendicular to the direction flight (across track) at a rate of 2.67 seconds per scan.