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

Abstract

[1] The Constellation Observing System for Meteorology Ionosphere and Climate (COSMIC)/Formosa Satellite 3 (FORMOSAT-3) is a six-satellite radio occultation mission that was launched in mid-April, 2006. 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. The RMS difference of electron density in the ionosphere between 150 and 500 km altitude for collocated occultations is about 10 3 cm À3 .

Long-term comparison of the ionospheric F2 layer electron density peak derived from ionosonde data and Formosat-3/COSMIC occultations

“…It was concluded that the accuracy of NmF2 yields around 20% of its absolute level, which was later confirmed by Tsai et al (2001). Furthermore, to estimate the absolute precision of the classical Abel inversion, Schreiner et al (2007) studied the accuracy of N e by co-located F-3/C EDPs and obtained a root-mean-square (RMS) difference of approximately 10 9 el/m 3 , a value which indicates already, that rough discrepancies cannot be ruled out by using the classical approach.…”

Enhanced E-layer ionization in the auroral zones observed by radio occultation measurements onboard CHAMP and Formosat-3/COSMIC

“…Rocken et al, 2000;Schreiner et al, 2009). The comparison of CHAMP electron density profiles with electron density profiles deduced from the radio occultation measurements onboard the Formosat-3/COSMIC satellites, which are provided by the data center TACC/CDAAC, revealed good agreement with a RMS of less than 1.4×10 11 m −3 for NmF2, cf.…”

Forecast impact experiment with a constellation of GPS radio occultation receivers

“…A summary of the mission objectives and early results with COSMIC/FORMOSAT-3 (referred to as COSMIC hereafter) is given by Anthes et al (2008). In addition, Schreiner et al (2007) have shown that refractivity profiles derived from the COS-MIC measurements have a precision of ∼0.2% of the observed value, between heights of 10 and 20 km.…”