Accurate quantification of the algebraic,multiplicative algebraic,and simultaneous iterative reconstruction techniques in ionosphere rebuilding based on the TIEGCM assessment

The algebraic reconstruction technique(ART),multiplicative algebraic reconstruction technique(MART),and simultaneous iterative reconstruction technique(SIRT)are computational methodologies extensively utilized within the field of computerized ionospheric tomography(CIT)to facilitate three-dimensional reconstruction of the ionospheric morphology.However,reconstruction accuracy elicits recurrent disputes over its practical application,and people usually attribute this issue to incomplete and uneven coverage of the measurements.The Thermosphere Ionosphere Electrodynamics General Circulation Model(TIEGCM)offers a reasonable physics-based ionospheric background and is widely utilized in ionospheric research.We use the TIEGCM simulations as the targeted ionosphere because the current measurements are far from able to realistically reproduce the ionosphere in detail.Optimized designations of satellite measurements are conducted to investigate the limiting performance of CIT methods in ionospheric reconstruction.Similar to common practice,electron density distributions from outputs of the International Reference Ionosphere(IRI)model are used as the iterative initial value in CIT applications.The outcomes suggest that despite data coverage,iterative initial conditions also play an essential role in ionospheric reconstruction.In particular,in the longitudinal sectors where the iterative initial height of the F2-layer peak electron density(hmF2)differs substantially from the background densities,none of the three CIT methods can reproduce the exact background profile.When hmF2 is close but the ionospheric F2-layer peak density(NmF2)is different between the targeted background and initial conditions,the MART performs better than the ART and SIRT,as evidenced by the correlation coefficients of MART being above 0.97 and those of ART and SIRT being below 0.85.In summary,this investigation reveals the potential uncertainties in traditional CIT reconstruction,particularly when realistic hmF2 or NmF2 values differ substantially from the initial CIT conditions.

Preliminary observation results of the Coherent Beacon Systemonboard the China Seismo-Electromagnetic Satellite-1

This paper reports, for the first time, observation results of the Coherent Beacon System(CBS) onboard the China SeismoElectromagnetic Satellite-1(CSES-1). We describe the CBS, and the Computerized Ionospheric Tomography(CIT) algorithm program is validated by numerical experiment. Two examples are shown, for daytime and nighttime respectively. The Equatorial Ionization Anomaly(EIA) can be seen, and the northern crest core is located at ～20°N in the reconstruction image at 07:28 UTC on 20 July 2018(daytime).Disturbances are shown in the reconstruction image at 18:40 UTC on 13 July 2018(nighttime). We find that beacon measurements are more consistent with ionosonde measurements than model results, by comparing Nm F2 at three sites at Lanzhou, Chongqing, and Kunming; consistency with ionosonde measurements validates beacon measurements. Finally, we have studied Vertical Total Electron Content(VTEC) variations from ground to ～500 km(the height of CSES-1 orbit) and ratios of VTEC between beacon measurements and CODE(Center for Orbit Determination in Europe) data. VTEC variation from ground to ～500 km has a range of 7.2–16.5 TECU for the daytime case and a range of 1.1–1.7 TECU for the nighttime case. The Beacon/CODE ratio of VTEC varies with latitude and time. The mean Beacon/CODE ratio is 0.69 for the daytime case and 0.26 for the nighttime case. The fact that the nighttime case yields lower ratios indicates the higher altitude of the ionosphere during nighttime when the ionosphere is assumed to be a thin layer.