First results from the ionospheric tomography experiment using beacon TEC data obtained by means of a network along a longitude of 136°E over Japan

Abstract

A chain of newly designed GNU (GNU is not UNIX) Radio Beacon Receivers (GRBR) has recently been established over Japan, primarily for tomographic imaging of the ionosphere over this region. Receivers installed at Shionomisaki (33.45 • N, 135.8• E), Shigaraki (34.8 • N, 136.1 • E), and Fukui (36 • N, 136• E) continuously track low earth orbiting satellites (LEOS), mainly OSCAR, Cosmos, and FORMOSAT-3/COSMIC, to obtain simultaneous total electron content (TEC) data from these three locations, which are then used for the tomographic reconstruction of ionospheric electron densities. This is the first GRBR network established for TEC observations, and the first beacon-based tomographic imaging in Japanese longitudes. The first tomographic images revealed the temporal evolution with all of the major features in the ionospheric electron density distribution over Japan. A comparison of the tomographically reconstructed electron densities with the f o F 2 data from Kokubunji (35 • N, 139• E) revealed that there was good agreement between the datasets. These first results show the potential of GRBR and its network for making continuous, unattended ionospheric TEC measurements and for tomographic imaging of the ionosphere.

Real-Time Ionosphere Monitoring by Three-Dimensional Tomography over Japan

“…Ionospheric tomography, a concept which was first proposed by Austen et al , is an inversion technique for reconstructing the ionospheric density distribution from TEC measurements made by multiple receivers. Ionospheric tomography has been employed in various studies using GNSS as well as beacon satellites in low earth orbits (LEOs) . Using LEO beacon satellites that pass quickly overhead, one ground‐based receiver can obtain a set of a number of TEC measurements along the satellite track as a snap shot.…”

Mid-latitude Summer Nighttime Anomaly (MSNA) – observations and model simulations

“…with their mean profiles. These profiles are extracted from the tomographic images obtained from 10 July to 31 August, at local time (LT) centered on the 2-h period, and hence represents the variability within those 2 h. The total electron content (TEC) data for the tomographic reconstruction are obtained from the GRBR (GNU Radio Beacon Receiver, GNU is the acronym for GNU is Not Unix) network operational in Japan Thampi and Yamamoto, 2010). Two aspects of MSNA are clearly seen in this figure: (1) MSNA is absent at lower altitudes (for instance at 200 km and 225 km); the density at these low altitudes are greater at 14:00 LT than at 20:00 LT, and (2) MSNA is a feature that exists at altitudes near and above the ionospheric peak (very prominently at altitudes of ∼275-450 km), and less so at higher altitudes.…”

Comparison of FORMOSAT‐3/COSMIC radio occultation measurements with radio tomography

“…The Kokubunji data shown for comparison are the average values of July and August 2008. The individual observations also compared well [ Thampi and Yamamoto , 2010]. It must be remembered that the Kokubunji latitude is close to the center of the reconstruction, where maximum accuracy is expected.…”

“…Hence, IRI‐2007 is a very reasonable choice as the initial guess for the reconstruction along the northern midlatitude region. The details of the tomographic inversion procedure have been published [ Thampi et al , 2007; Thampi and Yamamoto , 2010]. Examples of the TEC data from the GRBR chain over Japan, the first few tomographic images, and validation of these images by comparison with f o F 2 observations have also been reported [ Thampi and Yamamoto , 2010].…”

“…The details of the tomographic inversion procedure have been published [ Thampi et al , 2007; Thampi and Yamamoto , 2010]. Examples of the TEC data from the GRBR chain over Japan, the first few tomographic images, and validation of these images by comparison with f o F 2 observations have also been reported [ Thampi and Yamamoto , 2010]. However, although IRI‐2007 has significantly improved from the previous versions as far as the representation of the topside densities are concerned [ Bilitza and Reinisch , 2008], the topside density values may be less accurate than the bottomside values, which in turn could affect the accuracy of the reconstruction of the topside electron densities.…”