"GPS time" will be maintained by NIST against IAT into the indefinite future. Thus, GPS-RO by its nature produces a measurement directly flowing from an SI standard. No calibration is ever required; each profile is absolute. Newer GPS-RO instruments of different design will always share this property. The measurements will remain stable at the level of International Atomic Time (better than one part in 10^14) for all time (see NIST). For this reason, GPS-RO is likely to supplant weather balloons as the fundamental reference standard for monitoring temperatures in the upper troposphere and stratosphere.

Above: The NIST-F1 cesium fountain atomic clock — the primary time and frequency standard for the United States.