Data Set Information
DATA_SET_NAME CASSINI RSS: IONOSPHERIC ELECTRON DENSITY PROFILES EDP1 V1.0
DATA_SET_ID CO-SSA-RSS-5-EDP1-V1.0
NSSDC_DATA_SET_ID
DATA_SET_TERSE_DESCRIPTION
DATA_SET_DESCRIPTION Data Set Overview : This data set contains the complete collection of the published Cassini radio occultation electron density profiles (EDP) of the Titan ionosphere as of September 2008. EDP files are stored as ASCII tables. The design of the Cassini spacecraft's tour of the Saturnian system permitted multiple radio occultations of Titan's ionosphere to be carried out. Of these, a group of four occultations was incorporated into the primary Cassini mission and the resulting EDP files are included in this archive. These occultations occured on Titan flybys T12(19 March 2006), T14(20 May 2006), T27(26 March 2007), and T31(28 May 2007). Of these, the first two probed middle latitudes in the Southern Hemisphere (14.3 degrees South and 36.3 degrees South for T12 and 19.7 degrees South and 21.3 degrees South for T14). The other two occultations made observations in polar and near-polar locations (74.6 degrees South and 60.6 degrees North for T27 and 75.4 degrees North and 74.0 degrees South for T31). All observations occurred near the terminator, with the entry measurements occurring on the dark side (solar zenith angle(SZA) 92.2 degrees to 95.8 degrees), and the exits on the sunlit side (SZA 85.7 degrees to 90 degrees). The exit measurements at midlatitudes were also near the dusk terminator. The following table provides a summary of the data: Obs Date File Name Ram (deg) SEP (deg) ---- ----------- ------------------------------- --------- --------- T12N 19 Mar 2006 S19TIIOC2006_078_0000_X_001.EDP 73.7 131.5 T12X 19 Mar 2006 S19TIIOC2006_078_0000_X_001.EDP 87.5 131.5 T14N 20 May 2006 S20TIIOC2006_140_1203_N_001.EDP 100.1 72.6 T14X 20 May 2006 S20TIIOC2006_140_1203_X_001.EDP 66.4 72.6 T27N 26 Mar 2007 S28TIIOC2007_085_0000_N_001.EDP 93.9 138.2 T27X 26 Mar 2007 S28TIIOC2007_085_0000_X_001.EDP 60.7 138.2 T31N 28 May 2007 S30TIIOC2007_148_1737_N_001.EDP 98.1 76.8 T31X 28 May 2007 S30TIIOC2007_148_1737_X_001.EDP 78.4 76.8 For more details see A.J. Kliore et al. (J. Geophys. Res., 113, A09317,doi:10.1029/2007JA012965, 2008). Parameters : Each EDP file contains a table of electron number density versus altitude, where the altitude is determined by height of the closest approach point of the radio line-of-sight relative to the surface of Titan. The tables also include the planetocentric north latitude, solar zenith angle, solar time, and standard deviation of the measurements. Processing : During the occultation period, Cassini transmits three sinusoidal radio signals of 0.94, 3.6 and 13 cm wavelength (Ka-, X-, and S-band respectively). They are coherently generated on board Cassini from a common ultrastable crystal oscillator (USO). Digital samples of the in-phase and quadrature signal components were recorded at multiple sampling rates and bandwidths using the open-loop Radio Science Receivers (RSR) of the DSN. The data in these archive are based on processing signals recorded at 1 kHz bandwidth. The RSR as well as all subsystems of the DSN are driven by a highly stable frequency and timing system based on a hydrogen maser. Accurate antenna pointing is required especially at higher frequencies (e.g., Ka-band). The RSR data are processed by first detecting the signal carrier via software. A phase-locked loop or a series of Fast Fourier Transforms are typical detection methods depending on factors such as the signal-to-noise ratio as well as frequency and amplitude dynamics. Once detected, the signal is upconverted to 'sky frequency' and then frequency residuals are produced by removing a model of the apparent relative motion between the spacecraft and ground station. These residulas contain the science information on the atmosphere/ionosphere of the planet and form the basic data from which the atmospheric and ionospheric properties are extracted. The procedures for the analysis and inversion of these data are described in detail in A.J. Kliore et al. (Space Sci. Rev. 115, 1-70, doi:10.1007/s11214-004-1436-y, 2004). The residuals are detrended by fitting a least squares straight line to the baseline data and subtracting it from the raw residuals. The residuals are then used to compute the refractive bending angle at each data time point. This requires a precise ephemeris of Cassini relative to Titan, iterative light propagation time solutions linking the spacecraft, Titan, and the DSN station. The gravitational field of Titan was assumed to be spherical. Once the refractive bending angle and its corresponding ray asymptote distance with respect to the center of refraction are computed for each data point, the Abel integral transform, assuming spherical symmetry, is used to invert these data and to produce a vertical profile of refractivity. Since the radio refractivity is proportional to the electron density times the inverse square of the frequency, the electron density can be determined, as the frequencies are known very precisely. The altitude is determined by height of the closest approach point of the radio line-of-sight relative to the surface of Titan. Data : The EDP directory contains all the data files (i.e., the electron density profiles), which are accompanied by detached PDS labels describing their contents. The naming convention of these data files is: sssttIOCyyyy_ddd_hhmm_[NX]_vvv.EDP where: sss - Cassini Sequence, during which the data were collected (for this data set, sss : S19, S20, S28 and S30) tt - target ID (for this data set, tt : TI, for Titan) IOC - Ionospheric Occultation yyyy_ddd_hhmm - year, day of year, hour, min, in Spacecraft Event Time (SCET), for the start of the observation, during which these data were collected. [NX] - N denotes entry occultation; X denotes exit occultation vvv - version number Software : None. Media/Format : The archival data set is written on DVD-R media. The DVD-R volumes conform to the 'UDF_ISO-9660_BRIDGE' structure as required by PDS.
DATA_SET_RELEASE_DATE 2010-12-01T00:00:00.000Z
START_TIME 2006-03-19T12:00:00.000Z
STOP_TIME 2007-05-28T12:00:00.000Z
MISSION_NAME CASSINI-HUYGENS
MISSION_START_DATE 1997-10-15T12:00:00.000Z
MISSION_STOP_DATE N/A (ongoing)
TARGET_NAME TITAN
TARGET_TYPE SATELLITE
INSTRUMENT_HOST_ID CO
INSTRUMENT_NAME RADIO SCIENCE SUBSYSTEM
INSTRUMENT_ID RSS
INSTRUMENT_TYPE RADIO SCIENCE
NODE_NAME Planetary Atmospheres
ARCHIVE_STATUS SUPERSEDED
CONFIDENCE_LEVEL_NOTE Overview : In general, this is a good data set. Review : This archival data set was reviewed by the Cassini Radio Science Team prior to submission to the Planetary Data System (PDS). Data Coverage and Quality : The data are contained in one volumes (DVD), CORS_1001, and they cover the complete collection of the published Cassini radio occultation electron density profiles of the Titan ionosphere as of September 2008. The table, which was included in the section 'Data Set Overview' of this document, provides a summary of the data. There are no known problems with this data set. Limitations : The limitations in this data set follow from the quality of the execution, which is described above under Data Coverage and Quality.
CITATION_DESCRIPTION Kliore, A.J., Cassini Radio Occultation Profiles of the Titan Ionosphere from Publications up to September 2008, CO-SSA-RSS-5-EDP1-V1.0, NASA Planetary Data System, 2010.
ABSTRACT_TEXT This data set contains the complete collection of the published Cassini radio occultation electron density profiles of the Titan ionosphere as of September 2008.
PRODUCER_FULL_NAME ELIAS BARBINIS
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