The use of ionosondes in GPS ionospheric tomography at low latitudes

Abstract

[1] A new technique is presented for the incorporation of ionosonde observations into GPS ionospheric tomography. This approach greatly improves the vertical resolution of the images when using independent incoherent scatter radar observations as ground truth, addressing a traditional weakness of tomographic techniques. Ionosonde observations are used to set vertical basis functions adaptively within the inversion as well as providing electron density information for direct assimilation. The technique also improves slant total electron content (TEC) accuracy in the vicinity of the ionosonde. An experiment was performed in the equatorial region of South America as a 6-day case study due to the availability of incoherent scatter and ionosonde data during this period. Preliminary results were validated with the Jicamarca incoherent scatter radar and independent GPS slant TEC observations. Using the incoherent scatter radar as ground truth for the vertical profile, the new technique reduces mean NmF2 error to À0.07 Â 10 11 electrons/m 3 compared with 0.27 Â 10 11 electrons/m 3 in a control run with no ionosonde data, while root-mean square error is now 0.5 Â 10 11 electrons/m 3 compared with 1.0 Â 10 11 electrons/m 3 in the control. The new technique also results in 0.1 km mean error in hmF2, compared with À3.9 km in the control, while root-mean square hmF2 error is around 40 km in both cases. Using independent slant TEC observations, the mean error is À0.36 TECU compared with 0.64 TECU in the control run, while root-mean square error is 3.55 TECU down from 4.02 TECU, suggesting the new technique also improves TEC values.

Ionospheric imaging in Africa

“…Receivers placed in coverage gaps will clearly improve imaging accuracy far more than those placed close to existing receivers. The inclusion of observations that provide detailed information on the vertical electron density profile, such as observations from ionosondes or radio occultation measurements, would also provide significant improvements to ionospheric imaging accuracy, as shown in Chartier et al [2012b].…”

On the Annual Asymmetry of High‐Latitude Sporadic F

“…Data coverage is good in both polar caps, although there are large gaps in the oceans in the southern hemisphere. Poorly resolved regions of the images are removed from the analysis using the adaptive resolution mapping technique described in Chartier et al ().…”

Ionospheric electron density profile estimation using commercial AM broadcast signals

“…However, due to the lack of horizontal ray paths the vertical precision obtained by CIT is not good. Researchers have proposed many methods to solve this problem, such as bringing in radio occultation data by carrying receivers on low Earth orbit (LEO) satellites (Tsai et al, 2001); employing ionosonde data (Garcı́a-Fernández et al, 2003, Ma et al, 2005; absorbing incoherent scatter radar observations (Chartier et al, 2012); and using the vertical ionograms, backscatter ionograms and CHAMP satellite data together (Fridman and Nickisch, 2001, Fridman et al, 2009, Zhao et al, 2010. These methods can improve the vertical precision to a certain degree; however, these methods cannot obtain high-precision imaging because of the sparseness of ionosondes.…”