Analytic Signal Depth from High Resolution Aeromagnetic Data over the Gongola Basin Upper Benue Trough Northeastern Nigeria

The study of high-resolution aeromagnetic data was carried out over the Gongola basin, upper Benue trough, northeastern Nigeria, for analytic signal depth determination. Total intensity magnetic map obtained from the data using the Oasis Montaj TM programming software was used to get the residual map by polynomial fitting, from where the analytic signal was obtained with the use of anomaly width at half the amplitude (X1/2). This was used to carry out depth estimations over the study area. The results showed that it peaks over the magnetic structure with local maxima over its edges (boundaries or contact), and the amplitude is simply related to magnetization, likewise results also showed that the depth estimates were in the range of 1.2 to 5.9 km and were calculated for contact, dyke/sill and horizontal cylinder respectively. The lowest values are from DD profiles, while the highs are from AA profiles. This work is important in identifying dykes, contacts and intrusives over an area.

Review of Curie point depth determination through different spectral methods applied to magnetic data

SUMMARY Spectral methods have been applied for more than 40 yr to calculate the depth to magnetic sources and the Curie point depth or Moho depth. Unfortunately, conceptual, theoretical and methodological errors, as well as, subjective approaches and lack of rigor in the application of the method are common. This has affected reproducibility, credibility and confidence in this method. We carried out a detailed mathematical and methodological revision of the spectral methods (centroid, spectral peak, forward and fractal methods) applied to magnetic data for the determination of the depth to magnetic sources. Moreover, a systematic analysis of more than 110 articles was done in order to compile and compare the different approaches and values of key parameters used by different authors in their calculations. We discuss difficulties, conditions and methodological procedures, as well as several misapplications and misinterpretation of the different methods.

Reionization optical depth determination from Planck HFI data with ten percent accuracy

We present an estimation of the reionization optical depth τ from an improved analysis of data from the High Frequency Instrument (HFI) on board the Planck satellite. By using an improved version of the HFI map-making code, we greatly reduce the residual large-scale contamination affecting the data, characterised in, but not fully removed from, the Planck 2018 legacy release. This brings the dipole distortion systematic effect, contaminating the very low multipoles, below the noise level. On large-scale polarization-only data, we measure τ = 0.0566−0.0062+0.0053 at 68% C.L., reducing the Planck 2018 legacy release uncertainty by ∼40%. Within the ΛCDM model, in combination with the Planck large-scale temperature likelihood, and the high-ℓ temperature and polarization likelihood, we measure τ = 0.059 ± 0.006 at 68% C.L., which corresponds to a mid-point reionization redshift of zre = 8.14 ± 0.61 at 68% C.L. This estimation of the reionization optical depth with 10% accuracy is the strongest constraint to date.