This ROM SAF data record is derived from measurements by the Radio Occultation (RO) instruments onboard the Metop satellites in low-Earth orbit. The RO technique utilizes the bending due to refraction of the GPS radio signals as they pass through the Earth's atmosphere. Each occultation event gives a vertical profile of atmospheric refractivity, from which temperature, pressure, and humidity are retrieved, and each Metop satellite observes about 650 atmospheric profiles per day. The data have a global coverage and are insensitive to clouds and the underlying surface.
The ROM SAF interim climate data record based on Metop data covers the time period from January 2017 and onwards, and is updated on a regular basis. It provides an extension of the corresponding Metop climate data record which stops in the end of 2016. The data are available as individual atmospheric profiles and as monthly means on a regular latitude-height grid. The atmospheric profiles, and the gridded monthly means, include several geophysical variables: the bending angle of the GPS signals, atmospheric refractivity, temperature and pressure in the so called 'dry' approximation, as well as temperature, pressure, and tropospheric humidity obtained by so called 1D variational retrieval (using background model data as a priori). This retrieval also include surface pressure. In addition, the ROM SAF data record include tropopause heights, both for individual atmospheric profiles and as gridded monthly means.
The bending angle data record constitute an interim FCDR, while the temperature and humidity data records constitute interim TCDRs of GCOS Essential Climate Variables (ECVs). Note that the ROM SAF data product GRM-29-I1 is an interim CDR providing an extension of the corresponding CDR, the ROM SAF data product GRM-29-R1.