R. Dutta-Roy

University of Bonn, Bonn, North Rhine-Westphalia, Germany

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Publications (16)52.57 Total impact

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    ABSTRACT: The Cassini/Huygens mission was launched in October 1997, and during the third orbit around Saturn, the Huygens probe was released on course to enter Titan's atmosphere. During the descent, six science instruments provided in situ and remote sensing measurements of Titan's atmosphere and surface. Doppler tracking was performed with two Earth-based radio telescopes, and a Very Long Base Interferometry (VLBI) experiment was carried out. Data acquisition began around 1500 km altitude and continued throughout the 2 h and 30 min descent and for 1 h and 12 min after landing. This unique set of data is available in the ESA Planetary Science Archive (PSA) and mirror imaged in the NASA Planetary Data System (PDS). This paper presents an overview of the process the Huygens Data Archiving Working Group followed to develop and ingest the data set. A description of the data sets is also given.
    Planetary and Space Science. 01/2008;
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    ABSTRACT: The signal strength of the Huygens Probe Channel B transmission to the Cassini Orbiter was monitored during the Probe descent through Titan's atmosphere on 14 January 2005. A model of the Probe motion during the mission was constructed to include Probe spin, coning motion and tilt caused by varying wind speeds. This simple model is sufficient to reproduce the most prominent features seen in the signal level measurements. It provides estimates of the coning and tilt angles as well as the direction of the Huygens coordinate axes over extended time intervals in the mission.
    Planetary and Space Science 01/2007; 55(13):1886-1895. · 2.11 Impact Factor
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    ABSTRACT: Large radio telescopes on Earth tracked the radio signal transmitted by the Huygens probe during its mission at Titan. Frequency measurements were conducted as a part of the Huygens Doppler Wind Experiment (DWE) in order to derive the velocity of the probe in the direction to Earth. The DWE instrumentation on board Huygens consisted of an ultrastable oscillator which maintained the high Doppler stability required for a determination of probe horizontal motion during the atmospheric descent. A vertical profile of the zonal wind velocity in Titan's atmosphere was constructed from the Doppler data under the plausible assumption of generally small meridional wind, as validated by tracked images from the Huygens Descent Imager/Spectral Radiometer (DISR). We report here on improved results based on data with higher temporal resolution than that presented in the preliminary analysis by Bird et al. (2005), corroborating the first in situ measurement of Titan's atmospheric superrotation and a region of strong vertical shear reversal within the lower stratosphere. We also present the first high-resolution display and interpretation of the winds near the surface and planetary boundary layer.
    Journal of Geophysical Research 01/2006; 111. · 3.17 Impact Factor
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    ABSTRACT: One of Titan's most intriguing attributes is its copious but featureless atmosphere. The Voyager 1 fly-by and occultation in 1980 provided the first radial survey of Titan's atmospheric pressure and temperature and evidence for the presence of strong zonal winds. It was realized that the motion of an atmospheric probe could be used to study the winds, which led to the inclusion of the Doppler Wind Experiment on the Huygens probe. Here we report a high resolution vertical profile of Titan's winds, with an estimated accuracy of better than 1 m s(-1). The zonal winds were prograde during most of the atmospheric descent, providing in situ confirmation of superrotation on Titan. A layer with surprisingly slow wind, where the velocity decreased to near zero, was detected at altitudes between 60 and 100 km. Generally weak winds (approximately 1 m s(-1)) were seen in the lowest 5 km of descent.
    Nature 01/2006; 438(7069):800-2. · 38.60 Impact Factor
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    ABSTRACT: Coordinated ground-based observations of Titan were performed around or during the Huygens atmospheric probe mission at Titan on 14 January 2005, connecting the momentary in situ observations by the probe with the synoptic coverage provided by continuing ground-based programs. These observations consisted of three different categories: (1) radio telescope tracking of the Huygens signal at 2040 MHz, (2) observations of the atmosphere and surface of Titan, and (3) attempts to observe radiation emitted during the Huygens Probe entry into Titan's atmosphere. The Probe radio signal was successfully acquired by a network of terrestrial telescopes, recovering a vertical profile of wind speed in Titan's atmosphere from 140 km altitude down to the surface. Ground-based observations brought new information on atmosphere and surface properties of the largest Satumian moon. No positive detection of phenomena associated with the Probe entry was reported. This paper reviews all these measurements and highlights the achieved results. The ground-based observations, both radio and optical, are of fundamental imnortance for the interpretatinn of results from the Huygens mission.
    Journal of Geophysical Research 01/2006; · 3.17 Impact Factor
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    ABSTRACT: The Huygens Doppler Wind Experiment was designed to determine the strength and direction of Titan's zonal winds during the probe descent. The Doppler shift of the Huygens 2040 MHz carrier signal, driven by a stable rubidium clock, was monitored at a number of large radio telescopes on Earth. A height profile of Titan winds has been derived from frequency measurements recorded at the Green Bank Telescope in West Virginia and the Parkes Radio Telescope in Australia. The zonal wind was found to be eastward (prograde) for most of the atmospheric descent, providing the first in situ confirmation of superrotation on Titan, and reached a top speed of more than 100 m/s at altitudes near 125 km. A layer of surprisingly slow wind, where the velocity decreased to near zero, was observed at altitudes in the range 60 to 100 km. Very weak westward (retrograde) winds were inferred for most of the near-surface phase of descent below 5 km.
    07/2005; 37:620.
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    ABSTRACT: The ESA Huygens Probe entered and descended for nearly 2.5 hours through the atmosphere of Titan on 14 January 2005. Huygens survived impact on the surface and continued its telemetry broadcast to the NASA Cassini spacecraft on two separate radio links, denoted Channels A and B, respectively, for an additional 1.2 hours. The instrumentation for the Huygens Doppler Wind Experiment (DWE) consisting of two Ultra-Stable Oscillators in the transmitter (TUSO) and receiver (RUSO), were implemented only in Channel A. Whereas Channel B functioned flawlessly during the entire mission, the receiver for Channel A was never able to lock onto the Huygens signal because the DWE-RUSO had not been properly programmed into the critical probe radio relay sequence. All data on Channel A, including the DWE measurements and probe telemetry, were thus lost. In spite of this setback, the Channel A signal was successfully received at many radio telescopes on Earth. The precision of these Doppler measurements, considered as an aggregate, is roughly equivalent to that which had been foreseen from the measurements on board Cassini. We present an overview of the DWE ground-based observations and the Titan wind profile derived from them.
    AGU Spring Meeting Abstracts. 04/2005; -1:02.
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    ABSTRACT: The primary objective of the Doppler Wind Experiment (DWE), one of the six scientific investigations comprising the payload of the ESA Huygens Probe, is a determination of the wind velocity in Titan's atmosphere. Measurements of the Doppler shift of the S-band (2040 MHz) carrier signal to the Cassini Orbiter and to Earth were recorded during the Probe descent in order to deduce wind-induced motion of the Probe to an accuracy better than 1 m s-1. An experiment with the same scientific goal was performed with the Galileo Probe at Jupiter. Analogous to the Galileo experience, it was anticipated that the frequency of the Huygens radio signal could be measured on Earth to obtain an additional component of the horizontal winds. Specific secondary science objectives of DWE include measurements of: (a) Doppler fluctuations to determine the turbulence spectrum and possible wave activity in the Titan atmosphere; (b) Doppler and signal level modulation to monitor Probe descent dynamics (e.g., spinrate/spinphase, parachute swing); (c) Probe coordinates and orientation during descent and after impact on Titan.
    02/2005;
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    Robindro Dutta-Roy, Michael K. Bird
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    ABSTRACT: A Doppler Wind Experiment (DWE) will be performed during the Titan atmospheric descent of the ESA Huygens Probe. The direction and strength of Titan's zonal winds will be determined from the start of mission at an altitude of ~160 km down to the surface. The Probe's wind-induced horizontal motion will be derived from the residual Doppler shift of its S-band radio link to the Cassini Orbiter, corrected for all known orbit and propagation effects. We present an error analysis with the purpose of determining the largest error sources and some simulation results.
    01/2004; 544:109-116.
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    ABSTRACT: Scientists utilize the telecommunication links between spacecraft and Earth to examine changes in the phase/frequency, amplitude, line-width, or polarization, as well as round-trip light time, of radio signals to investigate: planetary atmospheres and ionospheres, planetary rings, planetary surface characteristics, shapes, gravitational fields, orbital motion and dynamics of solar system bodies, magnetic fields of the Sun and planets, the solar wind and corona, cometary atmospheres, gravitational waves, gravitational redshift, relativistic time-delay, and other phenomena. Recommendations are made to maintain and expand the existing strong science capabilities in the network, carry them into the next generation DSN, continue advancing the technology to improve sensitivity, and to enable future experiments via an efficient multi-mission system that reduces cost via remote and automated operations. This report is dedicated to the memory of George M. Resch, who passed away on November 22, 2001.
    07/2002; 272:355-360.
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    ABSTRACT: A Doppler Wind Experiment (DWE) will be performed during the Titan atmospheric descent of the ESA Huygens Probe. The direction and strength of Titan's zonal winds will be determined with an accuracy better than 1 m s−1 from the start of mission at an altitude of ∼160 km down to the surface. The Probe's wind-induced horizontal motion will be derived from the residual Doppler shift of its S-band radio link to the Cassini Orbiter, corrected for all known orbit and propagation effects. It is also planned to record the frequency of the Probe signal using large ground-based antennas, thereby providing an additional component of the horizontal drift. In addition to the winds, DWE will obtain valuable information on the rotation, parachute swing and atmospheric buffeting of the Huygens Probe, as well as its position and attitude after Titan touchdown. The DWE measurement strategy relies on experimenter-supplied Ultra-Stable Oscillators to generate the transmitted signal from the Probe and to extract the frequency of the received signal on the Orbiter. Results of the first in-flight checkout, as well as the DWE Doppler calibrations conducted with simulated Huygens signals uplinked from ground (Probe Relay Tests), are described. Ongoing efforts to measure and model Titan's winds using various Earth-based techniques are briefly reviewed.
    Space Science Reviews 06/2002; 104(1):613-640. · 5.52 Impact Factor
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    ABSTRACT: Doppler data from the Voyager 1 radio occultation of Titan were reprocessed in an attempt to detect an ionosphere. The original analysis (Lindal et al., 1983) provided only upper bounds on the peak electron density of 3000 cm(-3) (ingress: evening terminator) and 5000 cm(-3) (egress: morning terminator). The raw recordings were used to generate a longer baseline prior to occultation ingress (S-band and X-band data available) and after occultation egress (only S-band). The primary result was a positive detection of Titan's ionosphere with a maximum electron density of 2400+/-500 cm(-3) at an altitude of 1180+/-150 km. There is a hint that this main peak actually splits into two layers, as would be expected from numerical models of Titan's upper ionosphere that invoke both photoionization and energetic electron impacts. Convincing detections of the main ionospheric peak were also obtained using only the S-band data for both ingress and egress.
    08/1998; 30:1093.
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    ABSTRACT: The Doppler Wind Experiment (DWE) is one of six investigations to be performed during the Titan atmospheric descent of the ESA Huygens Probe. The primary scientific objective is to measure the direction and strength of Titan's zonal winds with an accuracy better than 1 m/s. The Probe's wind-induced horizontal motion will be derived from the residual Doppler shift of its S-band radio link to the Cassini Orbiter, corrected for all known orbit and propagation effects, from the beginning of the mission (altitude: approx. 160 km) down to impact on the surface. The DWE Instrumentation consists of Rb-based Ultra-Stable Oscillators used to: (1) generate the transmitted signal from the Probe and (2) extract the frequency of the received signal on the Orbiter. The capabilities of these USOs under the rugged experimental conditions on Titan and some results from the DWE pre-launch test program are described.
    09/1997;
  • M.K. Bird, R. Dutta-Roy, S.W. Asmar, T.A. Rebold
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    ABSTRACT: Evidence for a marginal detection of the Titan ionosphere has been obtained from a new analysis of the dual-frequency Doppler data recorded during theVoyager 1occultation in 1980. The original report by Lindalet al.(1983,Icarus53,348–363) gave only upper bounds on the peak electron density of 3000 cm−3during ingress (evening terminator) and 5000 cm−3during egress (morning terminator). The dual-frequency ingress data imply a maximum electron density of 2400 ± 1100 cm−3for Titan's upper ionosphere at an altitude of 1180 ± 150 km. The egress data were determined to be of limited use for this analysis because the X-band signal was received for only a few seconds. Nevertheless, a distinct ionospheric peak is revealed in the S-band data for both ingress and egress. The height and peak density of this ionized layer are in good agreement with expectations from numerical models that invoke photoionization and energetic electron impacts.
    Icarus. 01/1997;
  • R. Dutta-Roy, M. K. Bird
    01/1995;
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    ABSTRACT: Determination of the descent trajectory of the Huygens Probe during its descent through the atmosphere of Titan on 14 January 2005 is currently under construction. Toward this purpose, measurements from various on-board experiments and system instruments are combined to retrieve the altitude, descent speed and horizontal motion. This task is coordinated by the Huygens Descent Trajectory Working Group (DTWG). The Doppler Wind Experiment (DWE) was designed to retrieve the zonal (east-west) velocity of Huygens. No other on-board experiment can provide this parameter with comparable accuracy. The ground track can also be retrieved from images of the Descent Imager/Spectral Radiometer Experiment (DISR), albeit with less accuracy. Here we present a comparison of the ground tracks retrieved by DWE and DISR. We show that these two independent retrievals of the horizontal motion of Huygens are remarkably consistent.

Publication Stats

217 Citations
52.57 Total Impact Points

Institutions

  • 2006–2008
    • University of Bonn
      • Argelander-Institute of Astronomy
      Bonn, North Rhine-Westphalia, Germany
  • 2005
    • Joint Institute for VLBI in Europe
      Hoogeveen, Drenthe, Netherlands