Estimates of the precision of GPS radio occultations from the COSMIC/FORMOSAT-3 mission

The close proximity of the COSMIC satellites provides a unique opportunity to estimate the precision of the radio occultation remote sensing technique from closely collocated occultations (<10 km separation of tangent points).

The RMS difference of refractivity between 10 and 20 km altitude is less than 0.2%, which is approximately twice better than previous estimates obtained from CHAMP and SAC-C collocated occultations, apparently, due to smaller separation of the occultation pairs and due to parallel occultation planes. In the lower troposphere, the maximal RMS is ~0.8% at 2 km altitude and decreases abruptly to ~0.2% between 6 and 8 km altitude.