Bistatic observations of Titan's surface with the Huygens probe radio signal

Abstract

Huygens provided an unanticipated bistatic radio scattering experiment from Titan's surface. After a successful entry and descent on Titan, on 14 January 2005, the probe remarkably survived the landing and continued radioing from the surface to the overflying Cassini, until the orbiter set below Titan's local horizon. Here we report high‐quality measurements of the 2098 MHz (14.3 cm) postlanding radio signal, focusing on the striking variations observed in signal strength. The mechanism that creates this fading pattern is physically interpreted as multipath interference between the direct signal and the signal reflected on Titan's surface. The geophysical aspects that could bear on the signal analysis are described.

The electrical properties of Titan’s surface at the Huygens landing site measured with the PWA–HASI Mutual Impedance Probe. New approach and new findings

“…Additional geometric information on the resting position of Huygens Probe from parallax in the camera system, and the sharpness of focus of features on the ground indicates (Karkoschka et al, 2007) that the camera window was 48±2cm above the groundessentially equivalent to the base of the probe being 1±2cm above ground level. This is also consistent with a weaker but entirely independent constraint derived from the multipath interference pattern seen in the probe radio signal, which indicates the phase center of the antenna to be 75±5cm above the ground, or that the base of the probe was 1±5cm above ground level (Pérez-Ayúcar et al, 2006).…”

“…(Fulchignoni et al, 2005;Grard et al, 2006;Simões, 2007, Hamelin et al, 2007López-Moreno et al, 2008), and revealed the existence of an atypical Schumann resonance that implies the presence of a subsurface water ocean (Béghin, Hamelin and Sotin, 2010). Following the successful landing of Huygens, the operation of PWA was extended for approximately 32 min measuring the electrical properties of the ground until the end of the HASI measurement cycle, and also recording the weak 36 Hz signal of the Schumann resonance (Béghin et al, 2013), while the data link to the orbiter lasted for 40 min more (Pérez-Ayúcar et al, 2006).…”

Orbital bistatic radar observations of asteroid Vesta by the Dawn mission

“…Over the past decades, orbital BSR experiments have been used to assess the textural (and in some cases, dielectric) properties of the surfaces of terrestrial bodies such as Mercury 2 , Venus 3 , the Moon 4 – 6 , Mars 7 , 8 , Saturn’s moon Titan 9 , and now comet 67P/CG 10 . In contrast to most orbital BSR experiments, Dawn’s HGA beam intersected Vesta’s surface at grazing angles of incidence near 89° and in a microgravity environment with substantial variability in its gravity field 11 , leading to a low and variable orbital velocity and hence a more challenging detection of the Doppler-shifted surface echo (hereafter simply referred to as the “surface echo”).…”

Twilight on Ligeia: Implications of communications geometry and seasonal winds for exploring Titan’s seas 2020–2040

“…6, with a conservative elevation threshold of 10 o . Depending on the sea state and the antenna beam pattern, such an elevation should be relatively free of multipath effects (which were observed in the Huygens telemetry link to Cassini, Pérez-Ayú car et al, 2006) or atmospheric attenuation. Furthermore, only pathological shoreline topography (i.e.…”