Voyager 1 Radio Science Subsystem (RSS) Titan Radio Occultation, Version 1.0, 0.00001 s Raw Data

* Data Set Overview\n* =================\n\nThis Data Set consists of Raw Data collected during the Titan Radio Occultation of Voyager 1 in November 1980 plus ancillary Files that might be useful in Analysis of those Data. The Raw Data are sampled Voltage Outputs from Receivers tuned to the Voyager Carrier Frequencies at both S-band and X-band during the Occultations. The Data have been reduced to give Profiles of Atmospheric Temperature and Pressure as a Function of Height above the Surface on both the Ingress and Egress Sides of Titan (Lindal et al., 1983) and to make a marginal Detection of an Ionosphere (Bird et al., 1997).\n\nDuring the Titan Occultation, the Voyager 1 Spacecraft provided a coherent, dual-frequency Microwave Radio Signal Source. The Signal Frequency was derived from a precision, onboard Ultra-Stable Oscillator (USO). The Spacecraft High-Gain Antenna (HGA) beamed that Signal through the Atmosphere of Titan. As the Spacecraft moved on its Trajectory, the Radio Signal probed different Levels in the Atmosphere. An Hour later the Signals were received by Antennas of the NASA Deep Space Network (DSN) on Earth.\n\nBecause the Density of the Atmosphere of Titan was so poorly known prior to the Voyager Encounter, Experiment Planners did not know how much refractive Bending to expect during the Observations. Models predicted a Range of Behaviors from very little bending to so much that the narrow Beam from the Spacecraft HGA would be deflected away from Earth and the Surface Occultation would not be seen. Timing Uncertainties in the Motion of the Spacecraft with respect to Titan only complicated the Problem. The Experiment was implemented with a very small (0.11°) fixed HGA Offset during the Ingress Occultation and a large (2.36°) Offset during Egress. These Choices, in retrospect, were very good given the Atmosphere that was found.\n\n* Parameters\n* ==========\n\n The Output of the S-band Receiver was a Sinusoidal Carrier Signal embedded in Noise with a Bandwidth approximately 50 kHz and sampled at 300000 samples per second. The X-band Receiver Output was similar; but, because of greater potential for Doppler Drift and Prediction Uncertainty, its Bandwidth was 150 kHz and Sampling Rate was 300000 samples per second. Voltages typically were in the Range of ±10 V, but the absolute Levels were not calibrated. In fact, they are generally not needed since it is the Frequency (or Phase) of the Signal (rather than Amplitude) that is most useful in inferring Properties of a Neutral Atmosphere or Ionosphere.\n\nThe Frequency of the USO was known from monitoring during the Jupiter-Saturn Cruise (and from post-Saturn Observations). Doppler Contributions from Motions of the Spacecraft, Earth, Titan, and other Bodies of the Solar System were determined jointly with the Voyager Navigation Team. Relativistic Doppler Contributions could be estimated from proximity to large Masses. Receiver Tuning was recorded in POCA (Programmable Oscillator Control Assembly) Files, which are included with this Archive.\n\n* Processing\n* ==========\n\nNo Processing per se has been carried out on these Data. However, because of the high Sampling Rate, the 8-bit Samples were recorded originally on wide-bandwidth Analog Video Tape. The Analog Tapes were then replayed later at slower Speeds and the Digital Data were extracted and separated onto Computer Compatible Tapes (CCTs) with S-band and X-band Data on different Sets of Tapes. Because the S-band Data had been oversampled originally (300 ksps for a 50 kHz Bandwidth), only one of every three Samples was saved during the Transfer of S-band Data to CCTs. This Process, known as $quot;decimation$quot; meant that 300 s of Data could be stored on an S-band CCT whereas only 100 s of X-band Data would fit.\n\nBecause Analog Recording Technology was required to save the high data rate Digital Samples, there are occasional Dropouts in the Sample Stream. These can be detected by paying special attention to Counter Fields in Data Record Headers.\n\nTwo Analog Recorders (A and B) were available at each DSN Complex. Because a single Recorder could not capture the entire Set of Titan Occultation Activities, the two were run in parallel with staggered Start/Stop Times. Most Data were collected using Recorder A, but Recorder B was used to capture the Samples while Recorder A was being reloaded.\n\n* Data\n* ====\n\nPrimary Data were delivered to Voyager Radio Science Team Members in the Form of 30 megabyte (MB) CCTs covering 300 s (S-band) or 100 s (X-band). Each Tape had 6000 Records of 5056 bytes (56 bytes of Header Information and 5000 8-bit Samples of Receiver Output Voltage). Tapes were numbered sequentially as CCTs were generated from the High Density Video Originals. Tapes with Titan data from Recorder A were numbered VJ6281 through VJ6360; Tapes from Recorder B were numbered VJ6361 through VJ6380. Test and Calibration Data after the Titan Encounter were collected on Recorder A and have Numbers VJ6589 through VJ6594.\n\nThe original Tape Numbering has been preserved in the current File Names, which have the Form VJnnnnCC.ODR. On Tapes where one or more Records could not be read, the original has been separated into two or more Files. The Character $quot;C$quot; indicates the ordering of these File Fragments with $quot;A$quot; being first (and the Default with no Tape reading Errors), $quot;B$quot; next, etc.\n\nEach original D

Tags: waves-active
Organization: National Aeronautics and Space Administration