The Marine-Atmospheric Emitted Radiance Interferometer (MAERI) instrument measures downwelling longwave radiation at a very high spectral resolution and was located at the port bridge-roof wing on the 7th deck. The isntruments alternates sensing radiation at a 45° upward angle, horizontally straight out from the ship, at a 45° downward angle and into a chilled calibration cavity. In addition to the high-resolution frequency spectra from the upward scans, all scans provide information that can be converted to a radiative temperature. Hence, it measures very accurately both cloud-base, ambient air, and surface temperatures.