2006
DOI: 10.1016/j.pss.2006.05.036
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Electric properties and related physical characteristics of the atmosphere and surface of Titan

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Cited by 52 publications
(73 citation statements)
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“…3). A similar transition applies to the VLF range (not seen here), which also contains valuable data (Grard et al, 2006), put forward in Section 7 for the interpretation of the ELF noise. The spectrogram obtained during the first phase of the Huygens descent is enlarged in Fig.…”
Section: Observationsmentioning
confidence: 70%
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“…3). A similar transition applies to the VLF range (not seen here), which also contains valuable data (Grard et al, 2006), put forward in Section 7 for the interpretation of the ELF noise. The spectrogram obtained during the first phase of the Huygens descent is enlarged in Fig.…”
Section: Observationsmentioning
confidence: 70%
“…2); (ii) a broadband noise almost simultaneous with the "36 Hz" line enhancement, extends from the lowest spectral line (6 Hz) to the uppermost one (96 Hz), and even stretches in the VLF range, up to about 1 kHz (not shown here); a second enhancement of the broadband noise only is observed from about 22 km down to the surface; (iii) a small and steady increase of the central frequency of the "36 Hz" line, corresponding to an overall variation of about 1.5 Hz, is seen throughout the descent (Simões et al, 2007a); (iv) the first broadband signal enhancement occurs at about 109 km, about 36 s (∼1.7 km) after the jettison of the main parachute and firing of the stabilizing drogue parachute, and vanishes off at about 80 km, just above the sudden rise of the conductivity layer ( Fig. 3) discovered with the PWA instrument (Grard et al, 2006;Hamelin et al, 2007); (v) the maximum amplitude of the "36 Hz" line occurs between 70 and 105 km; it reaches a surprisingly high input level at the dipole antenna (45 mV rms), which corresponds to a spectral density of some 16 mV m −1 Hz −1/2 for an electric component aligned with the antenna whose effective length is about 1.6 m; the average level lies between 2 and 4 mV m −1 Hz −1/2 throughout the rest of the descent; (vi) the largest fluctuations of the "36 Hz" strength happen when the descent velocity and the tilt angle of the payload with respect to the vertical are the most variable; (vii) no harmonic or sub-harmonic of the "36 Hz" line is clearly identified within the dynamic range of the instrument during the first period; however, a weak but visible second line appears progressively at around 60-66 Hz, more pronounced artificially when it is superimposed on the broadband noise, from about 22 km downwards (Fig. 3); (viii) the second enhancement period of the broadband ELF-VLF noise at around 22 km exhibits a frequency spectrum similar to that of the first one, in shape and strength; the artificial increase at 61 km is due to the abovementioned operation-mode change; contrary to the first event, the variation in broadband noise is not accompanied by any significant increase of the "36 Hz" amplitude.…”
Section: Observationsmentioning
confidence: 86%
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“…As a useful comparison, this is 10 times less than the last measurements performed during the last phase of the descent and 4 to 6 seconds after touch down (Béghin et al, 2012). However, since the main component of the conventional SR modes is known to be vertical, the estimate of the actual strength of the incident wave-field vector is most questionable, as it depends on the Huygens motion and tilt of the boom with respect to the local vertical, and whether the sensors are free or in direct electric contact with a lossy dielectric ground (Grard et al, 2006;Béghin et al, 2012).…”
Section: Discussionmentioning
confidence: 99%
“…For instance, the value measured by the Y-tilt sensor seems to indicate still a permanent tilt of 2 • after offset correction. On the other hand, the mutual impedance (MI) device, a component of the HASI-PWA instrument, designed to measure the ground conductivity and using partly the same sensors as the ELF dipole antenna (Grard et al, 2006), experienced a regular decay in sensitivity from 10 s after impact before reaching an average stable value (i.e., a behavior compatible with that of the ELF bin 36 data). Such coincidence, still under investigation, could perhaps be caused by some motion of at least one of the boom-antenna without any perceptible influence on the Y-tilt sensor.…”
Section: Discussionmentioning
confidence: 99%