Analysis of the bias berween TOPEX and GPS vTEC determinations

AZPILICUETA, F.; BRUNINI, C.; GENDE, M.

Cairns, Australia.

Congreso; 2005 IAG/IAPSO/IABO Joint Assembly; 2005

Since the availability of TOPEX vertical TEC (vTEC) measurements several validation studies against vTEC determinations from other sources have been performed. Many of these studies have identified a vTEC constant bias between +3 and +5 TECu (TOPEX greater than the others) when they are compared to GPS and DORIS vTEC determinations. Based on La Plata Ionospheric Model, global vTEC maps have been computed on a day to day basis for years 1998 and 1999, and compared to TOPEX vTEC determinations. This comparison confirms a constant bias ranging from +3 to +3.6 TECU. The available documentation provided by TOPEX processing centers relative to the computation of geophysical data records, reports that a constant correction of +15 mm is applied to the final range computed by the TOPEX altimeter for the analyzed period. This correction is empirically applied to eliminate the discrepancy between TOPEX and Poseidon range measurements and to solve sea level height calibration problems of TOPEX altimeter. In the present contribution we propose that the TOPEX-GPS vTEC bias and the TOPEX sea level height bias could be both explained by a miss-calibration on the range corrections applied to TOPEX range determinations on both frequencies.