The Precise Range and Range Rate Equipment (PRARE) and its possible support to the radar altimeter measurement for ERS-1

The Precise Range and Range Rate Experiment (PRARE) which delivers slant range data with cm accuracy, is described, and its support for the ERS-1 radar altimeter (RA) is outlined. The PRARE can help to determine very precisely the orbit of ERS-1. It can measure the total electron content of the ionosphere, which is needed for the calculation of the ionospheric delay for the RA-signal. It can also support the along track scanning radiometer and the RA by collecting the meteorological data (pressure, temperature and moisture ground) which renders, with a proper model, the tropospheric delay of the tracking and RA signals. In all cases it is, however, necessary to consider more than the three ground stations foreseen.