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Geoscientific Instrumentation, Methods and Data Systems An interactive open-access journal of the European Geosciences Union
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Volume 2, issue 2
Geosci. Instrum. Method. Data Syst., 2, 237–248, 2013
© Author(s) 2013. This work is distributed under
the Creative Commons Attribution 3.0 License.
Geosci. Instrum. Method. Data Syst., 2, 237–248, 2013
© Author(s) 2013. This work is distributed under
the Creative Commons Attribution 3.0 License.

Research article 22 Oct 2013

Research article | 22 Oct 2013

Observation of 2nd Schumann eigenmode on Titan's surface

C. Béghin1, G. Wattieaux1,2, R. Grard3, M. Hamelin4, and J. P. Lebreton1,5 C. Béghin et al.
  • 1LPC2E-CNRS-Université d'Orléans, UMR7328, CNRS – 3A, Ave. Recherche Scientifique, 45071 Orléans Cedex 2, France
  • 2LAPLACE-CNRS-Université de Toulouse III, 118 route de Narbonne, 31062 Toulouse Cedex 9, France
  • 3SSD, ESA-ESTEC, European Space Agency, Keplerlaan 1 2200 AG Noordwijk, the Netherland
  • 4LATMOS-IPSL, Université Pierre et Marie Curie, 4, place Jussieu, 75252 Paris Cedex 05, France
  • 5LESIA, Observatoire de Paris- Section de Meudon, 5 place Jules Janssen, 92195 Meudon Cedex, France

Abstract. This work presents the results obtained from an updated data analysis of the observations of extremely low frequency (ELF) electromagnetic waves performed with the HASI-PWA (Huygens Atmospheric Structure and Permittivity, Wave and Altimetry) instrumentation after Huygens Probe landing on Titan's surface in January 2005. The most significant signals observed at around 36 Hz throughout the descent in the atmosphere have been extensively analyzed for several years, and subsequently interpreted as the signature of a Schumann resonance, although the latter exhibits atypical peculiarities compared with those known on Earth. The usual depicting methods of space wave data used so far could not allow for retrieving the presence of weak signals when Huygens was at rest for 32 min on Titan's surface. Whereas the expected signal seems hidden within the instrumental noise, we show that a careful statistical analysis of the amplitude distribution of the 418 spectral density samples of the 36 Hz line reveals abnormal characteristics compared to other frequencies. This behavior is shown to occur under propitious circumstances due to the characteristics of the onboard data conversion processes into digital telemetry counts, namely 8-bit dynamic after logarithm compression of the DFT (Discrete Fourier Transform) of ELF waveforms. Since this phenomenon is observed only at the frequency bin around 36 Hz, we demonstrate that the Schumann resonance, seen in the atmosphere within the same band is still present on the surface, albeit with a much smaller amplitude compared to that measured before and a few seconds after the impact, because the electric dipole is thought to have been stabilized ten seconds later almost horizontally until the end of the measurements.

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