IRI Workshop 2005 TEC Measurements with Dual-Frequency Space Techniques and Comparisons with IRI T. Hobiger, H. Schuh Advanced Geodesy, Institute of Geodesy and Geophysics, Vienna University of Technology, Vienna, Austria C.K. Shum, L. Potts, S. Ge Laboratory for Space Geodesy and Remote Sensing, The Ohio State University, Columbus, Ohio, USA D. Bilitza Raytheon ITSS, GSFC, SPDF, Code 612.4, Greenbelt, MD Dual frequency altimeters (TOPEX/POSEIDON, JASON-1, ENVISAT) - Global VLBI measurements spanning over two solar cycles - DORIS global tracking systems for various altimetric and SPOT-n satellites

IRI Workshop 2005 Satellite Band Frequencies OrbitTEC GPS L1/L2 1.5/1.2 GHz20,200 kmslant T/P Ku/C 13.6/5.3 GHz 1300 kmvertical Jason Ku/C 13.6/5.3 GHz 1300 kmvertical Envisat Ku/S 13.6/3.2 GHZ 800 kmvertical DORIS 2.0/ MHz km slant VLBI X/S 8.4/2.3 GHzslant DORIS = Doppler Orbitography and Radio positioning Integrated by Satellite L GHZ 1 TECU  16.2 cm delay Ku13.6 GHz1 TECU  2.2 mm delay

IRI Workshop 2005 VLBI

IRI Workshop 2005 VLBI DATA SOURCE AND ESTIMATION TECHNIQUE VLBI provides only baseline (=differential) measurements Adopted estimation method developed at Vienna University of Technology - station dependent VTEC values modelled by piece-wise linear functions - longitudinal rotation of datapoints equivalent to sun-fixed reference system - north-south variations described by linear gradients - adjustment algortithm prohibits negative TEC values Data from International VLBI Service for Geodesy & Astrometry Period: 1984 – 2005, depending on antenna involvement

IRI Workshop 2005

Map of all IVS VLBI stations

IRI Workshop 2005

Average of 20 years of data

IRI Workshop 2005 Altimeters

IRI Workshop 2005 Dual-Frequency Altimeters The ionosphere delay measured by dual frequency radar altimeters is in nadir direction over ocean and large lakes. TOPEX/Poseidon (T/P) and JASON-1 carry Ku band (13.6 GHz) and C band (5.3 GHz) altimeter flying in a 1300 km orbit, while ENVISAT with Ku band ( GHz) and S band (3.2 GHz) altimeter in 800 km orbit. The global sea level change study requires altimeter to be well calibrated and to have long term stability. Evaluate the error budget from ionosphere contributions is very important for sea level research. Due to the higher frequency of the altimeter instrument, the ionosphere delay is small comparing to GPS, e.g., 1 TECU causes 16.2 cm delay at L1, but only 2.2 mm delay at Ku band.

IRI Workshop 2005 Single-Frequency Altimeters Most historic altimeters (GEOSAT, etc) were single-frequency (Ku band) systems and relied on models for the computation of the ionospheric delay. IRI-95 was adopted to reprocess the GEOSAT Geophysical Data Record (GDR) (Lillibridge and Cheney, 1997) IRI-95 was used for the processing of the GEOSAT Follow On (GFO) Interim GDRs (Navy IGDR Users Handbook, 2000; NOAA GFO IGDR Format, 1998; Shum et al., 2001). ERS-1 and ERS-2 data products were computed using IRI-95 (CERSAT, 1996).

IRI Workshop 2005 Bilitza et al., 1996

IRI Workshop 2005

Shengjie Ge et al., AGU Fall, 2004 Equinoctial maxima Jump due to CODE processing problem

IRI Workshop 2005 (GIM=CODE) A 10 cm range correction was added to the C-band measurement to keep the dual-frequency ionosphere delays from being negatively biased and to agree with calibration and validations with ionosonde data (Imel, 1994). Range corrections of –20 mm and 130 mm were added to the TOPEX Side B altimeter Ku- band and C-band range measurements, respectively, based on comparisons with JPL GIM. Zhao et al., 2005

IRI Workshop 2005