A technique for routinely updating the ITU-R database using radio occultation electron density profiles

Well credited and widely used ionospheric models, such as the International Reference Ionosphere or NeQuick, describe the variation of the electron density with height by means of a piecewise profile tied to the F2-peak parameters: the electron density,$$N_m \mathrm{F2}$$NmF2, and the height, $$h_m \mathrm{F2}$$hmF2. Accurate values of these parameters are crucial for retrieving reliable electron density estimations from those models. When direct measurements of these parameters are not available, the models compute the parameters using the so-called ITU-R database, which was established in the early 1960s. This paper presents a technique aimed at routinely updating the ITU-R database using radio occultation electron density profiles derived from GPS measurements gathered from low Earth orbit satellites. Before being used, these radio occultation profiles are validated by fitting to them an electron density model. A re-weighted Least Squares algorithm is used for down-weighting unreliable measurements (occasionally, entire profiles) and to retrieve $$N_m \mathrm{F2}$$NmF2 and $$h_m \mathrm{F2}$$hmF2 values—together with their error estimates—from the profiles. These values are used to monthly update the database, which consists of two sets of ITU-R-like coefficients that could easily be implemented in the IRI or NeQuick models. The technique was tested with radio occultation electron density profiles that are delivered to the community by the COSMIC/FORMOSAT-3 mission team. Tests were performed for solstices and equinoxes seasons in high and low-solar activity conditions. The global mean error of the resulting maps—estimated by the Least Squares technique—is between $$0.5\times 10^{10}$$0.5×1010 and $$3.6\times 10^{10}$$3.6×1010 elec/m$$^{-3}$$−3 for the F2-peak electron density (which is equivalent to 7 % of the value of the estimated parameter) and from 2.0 to 5.6 km for the height ($$\sim $$∼2 %).

[1]  D. Bilitza,et al.  A global model for the height of the F2-peak using M3000 values from the CCIR numerical map , 1979 .

[2]  Le Roy Dougherty Weld,et al.  Theory of Errors and Least Squares , 2009, Nature.

[4]  J. Dudeney,et al.  A simple empirical method for estimating the height and semi-thickness of the F2-layer at the Argentine Islands, Graham Land , 1974 .

[5]  K. Rawer,et al.  Improving the M(3000)-hmF2 relation , 2004 .

[6]  P. A Bradley,et al.  A simple model of the vertical distribution of electron concentration in the ionosphere , 1973 .

[7]  Roger M. Gallet,et al.  Representation of diurnal and geographic variations of ionospheric data by numerical methods , 1962 .

[8]  Congliang Liu,et al.  A global model of the ionospheric F2 peak height based on EOF analysis , 2009 .

[9]  Norbert Jakowski,et al.  A new global model for the ionospheric F2 peak height for radio wave propagation , 2012 .

[10]  W. Wan,et al.  Modeling M(3000)F2 based on empirical orthogonal function analysis method , 2008 .

[11]  Christian Rocken,et al.  The COSMIC/FORMOSAT-3 Mission: Early Results , 2008 .

[12]  R. G. Lerner,et al.  Encyclopedia of Physics , 1990 .

[13]  M. Angling.  First assimilations of COSMIC radio occultation data into the Electron Density Assimilative Model (EDAM) , 2008 .

[14]  L. F. McNamara,et al.  Improved world-wide maps of monthly median foF2 , 1988 .

[15]  J. Sanz,et al.  Ground- and space-based GPS data ingestion into the NeQuick model , 2011 .

[16]  Sandro M. Radicella,et al.  A new version of the NeQuick ionosphere electron density model , 2008 .

[17]  Iwona Stanislawska,et al.  Towards a new reference model of hmF2 for IRI , 2008 .

[18]  Ying-Hwa Kuo,et al.  Satellite constellation monitors global and space weather , 2006 .

[19]  D. Bilitza,et al.  Measurements and IRI model predictions during the recent solar minimum , 2011, 2011 XXXth URSI General Assembly and Scientific Symposium.

[20]  Christian Rocken,et al.  Inversion and error estimation of GPS radio occultation Data , 2004 .

[21]  Bodo W. Reinisch,et al.  Deducing topside profiles and total electron content from bottomside ionograms , 2001 .

[22]  Claudio Brunini,et al.  Temporal and spatial variability of the bias between TOPEX- and GPS-derived total electron content , 2005 .

[23]  S. Weisberg.  Applied Linear Regression , 1981 .

[24]  Bodo W. Reinisch,et al.  International Reference Ionosphere 2000 , 2001 .

[25]  Douglas Hunt,et al.  Estimates of the precision of GPS radio occultations from the COSMIC/FORMOSAT‐3 mission , 2007 .

[26]  Peter J. Huber,et al.  Robust Statistics , 2005, Wiley Series in Probability and Statistics.

[27]  Xinan Yue,et al.  Error analysis of Abel retrieved electron density profiles from radio occultation measurements , 2010 .

[28]  Thomas P. Yunck,et al.  A History of GPS Sounding , 2000 .

[29]  Mohammed Mainul Hoque,et al.  A new global empirical NmF2 model for operational use in radio systems , 2011 .

[30]  Claudio Brunini,et al.  Analysis of the bias between TOPEX and GPS vTEC determinations , 2009 .

[31]  Norbert Jakowski,et al.  Radio occultation techniques for probing the ionosphere , 2004 .

[32]  C. Brunini,et al.  Improving SIRGAS Ionospheric Model , 2013 .

[33]  L. Libin,et al.  Forecasting of Ionospheric Critical Frequency Using Neural Networks , 2005, Chinese Journal of Space Science.

[34]  Dieter Bilitza,et al.  International reference ionosphere , 1978 .

[35]  T. Fuller‐Rowell,et al.  More total electron content climatology from TOPEX/Poseidon measurements , 2001 .

[36]  David N. Anderson,et al.  Maps of ƒ0F2 derived from observations and theoretical data , 1984 .

[37]  D. Bilitza,et al.  EQUATORIAL F2-LAYER PEAK HEIGHT AND CORRELATION WITH VERTICAL ION DRIFT AND M(3000)F2 , 2003 .

[38]  Christian Rocken,et al.  THE COSMIC/FORMOSAT-3 MISSION THE COSMIC/FORMOSAT-3 MISSION , 2008 .

[39]  Lj.R. Cander,et al.  Short-Term Prediction of foF2 using Time-Delay Neural Network , 1999 .

[40]  L. McKinnell,et al.  On the global model for foF2 using neural networks , 2005 .