DATA_SET_TERSE_DESC The Cassini Radio and Plasma Wave Science (RPWS) Quasi Thermal Noise (QTN) data set contains thermal plasma parameters derived by QTN spectroscopy analysis applied on data acquired with the High Frequency Receiver (HFR) during the perikrones of the entire mission. ABSTRACT_DESC The Cassini Radio and Plasma Wave Science (RPWS) Quasi Thermal Noise (QTN) data set contains thermal plasma parameters derived by QTN spectroscopy analysis applied on data acquired with the High Frequency Receiver (HFR) during the perikrones of the entire mission. This data set includes the total electron density and the core electron temperature, as well as the uncertainties on the measurements. It also includes ancillary data about the location of the spacecraft at the time of the measurement: distance to Saturn, local-time, kronographic latitude and dipolar L-Shell apex distance. Data are presented in CDF files, which contain a 1D array depending on time for each parameter. This data set is intended to be the most comprehensive and complete data set for thermal plasma parameters measured by the HFR in the Cassini RPWS archive. A browse data set is included with these data which provides for a graphical search of the data using a series of thumbnail and full-sized plots which lead the user to the particular data file(s) of interest. Indentification Product LID data collection urn:nasa:pds:cassini-rpws-hfr-qtn:data data product urn:nasa:pds:cassini-rpws-hfr-qtn:data:200406301642-200407010951-cdf urn:nasa:pds:cassini-rpws-hfr-qtn:data:200410280008-200410282357-cdf urn:nasa:pds:cassini-rpws-hfr-qtn:data:YYYYMMDDhhmm-YYYYMMDDhhmm-cdf browse collection urn:nasa:pds:cassini-rpws-hfr-qtn:browse browse product urn:nasa:pds:cassini-rpws-hfr-qtn:browse:200406301642-200407010951-plot urn:nasa:pds:cassini-rpws-hfr-qtn:browse:200410280008-200410282357-plot urn:nasa:pds:cassini-rpws-hfr-qtn:browse:YYYYMMDDhhmm-YYYYMMDDhhmm-plot thumbnail product urn:nasa:pds:cassini-rpws-hfr-qtn:browse:200406301642-200407010951-thumbnail urn:nasa:pds:cassini-rpws-hfr-qtn:browse:200410280008-200410282357-thumbnail urn:nasa:pds:cassini-rpws-hfr-qtn:browse:YYYYMMDDhhmm-YYYYMMDDhhmm-thumbnail document collection urn:nasa:pds:cassini-rpws-hfr-qtn:document index product urn:nasa:pds:cassini-rpws-hfr-qtn:document:index data version = 1.0 software version = 1.0 CITATION_DESC Schippers, P., M. Moncuquet, N. Meyer-Vernet, and A. Lecacheux (2013), "Core electron temperature and density in the innermost Saturn's magnetosphere from HF power spectra analysis on Cassini." J. Geophys. Res. Space Physics, 118, 7170-7180. 10.1002/2013JA019199 Moncuquet, Michel, et al. 2005. "Quasi Thermal Noise Spectroscopy in the Inner Magnetosphere of Saturn with Cassini/RPWS: Electron Temperatures and Density." Geophys. Res. Lett. 32: L20S02. 10.1029/2005GL022508 DATA_SET_DESC Data Set Overview ================= The Cassini Radio and Plasma Wave Science (RPWS) Quasi Thermal Noise (QTN) data set contains thermal plasma parameters derived by QTN spectroscopy analysis applied on data acquired with the High Frequency Receiver (HFR) during the perikrones of the entire mission. This data set includes the total electron density and the core electron temperature, as well as the uncertainties on the measurements. It also includes ancillary data about the location of the spacecraft at the time of the measurement: distance to Saturn, local-time, kronographic latitude and dipolar L-Shell apex distance. Data are presented in CDF files, which contain a 1D array depending on time for each parameter. This data set is intended to be the most comprehensive and complete data set for thermal plasma parameters measured by the HFR in the Cassini RPWS archive. A browse data set is included with these data which provides for a graphical search of the data using a series of thumbnail and full-sized plots which lead the user to the particular data file(s) of interest. Parameters ========== This data set comprises spacecraft event time, radial distance (in Saturn Radii) from Saturn, latitude (in deg), local time (in hours) and L-shell (in Saturn Radii) of the spacecraft, total electron number density (in cm-3) with the measurement uncertainty, core electron temperature (in eV) with the measurement uncertainty and quality flag that were acquired by QTN analysis on RPWS/HFR Spectra. Processing ========== The present data set was derived from the level two data of RPWS/HFR. The analysis was compiled by the LESIA team (Observatoire de Paris, Meudon, France). The total electron density is deduced from a strong signal peak near the upper-hybrid resonance (FuH), independently of any calibration. Indeed, the plasma frequency Fp can be derived from the FuH resonance and the gyrofrequency Fg (derived from magnetic field measurements by the Cassini/MAG instrument [1]): / 2 2 \ 1/2 Fp = | FuH - Fg | \ / The total electron density Ne is then obtained as: / 2 pi \ 2 2 Ne = Epsilon_0 m_e | ---- | Fp \ e / The error on the density was calculated on the basis of the uncertainty of the HFR receiver spectral relative resolution (df/f = 5%, 10% or 20%). The core electron temperature is deduced from the thermal plateau level Vmin^2 below FuH, given in [2] as a function of the core temperature Tc and Debye length LD (see Eq. 1 of [2]): 1/2 / oo 2 2 ( 2 m_e k_B Tc ) | F_V(kL) k L_D Vmin ~ 8 ---------------------------- | --------------- dk 3/2 2 | / 2 2 \2 pi Epsilon_0 (1+C_B/C_A) / O | k L_D + 1 | \ / (S.I. units), Vmin^2 in V^2/Hz. Here F_V(kL) is the Cassini V-shaped antenna response, with L the single wire length (L ~ 10m), pi Epsilon_0 L C_A= ---------------- ln(L_D / a) is the dipole antenna capacitance at low frequencies, with a the wire radius (a ~1.4 cm), and C_B is the base capacitance. We then use an iterative method to deduce T_c. The error on the temperature is determined a posteriori by estimating the averaged 1-sigma dispersion of the temperature level during the perikrone. References: [1] Dougherty, Michele, et al. 2004. “The Cassini Magnetic Field Investigation”, Space. Sci. Rev. 114: 331-383. [2] Moncuquet, Michel, et al. 2005. “Quasi Thermal Noise Spectroscopy in the Inner Magnetosphere of Saturn with Cassini/RPWS: Electron Temperatures and Density.” Geophys. Res. Lett. 32: L20S02. doi:10.1029/2005GL022508. [3] Schippers, P., M. Moncuquet, N. Meyer-Vernet, and A. Lecacheux (2013), “Core electron temperature and density in the innermost Saturn’s magnetosphere from HF power spectra analysis on Cassini.” J. Geophys. Res. Space Physics, 118, 7170–7180, doi:10.1002/2013JA019199. Data ==== The RPWS HFR QTN data set in included in CDF files. Each parameter is a 1D variable in the file, depending on time. The SCET of each sample corresponds to the beginning of the HFR sweep. Hence, the real measurement time can be up to about 2 s after that time, depending on the operating mode and on the value of FuH. Ancillary Data ============== Ancillary data are included in the files. They provide the location of the spacecraft at the time of the measurement (distance to Saturn, latitude, local time and L-Shell). Coordinate System ================= The data in this data set are thermal plasma parameters derived from HFR spectra using the thermal noise spectroscopy theory. These parameters are presented as detected by the sensor and are not rotated into any other coordinate system. If desired the SPICE kernels can be used with the SPICE toolkit to convert from the spacecraft frame to virtually any frame which may be of use in analyzing these data. However, for most purposes, the parameters may be considered point measurements at Cassini and may be entirely adequate with no coordinate transformations at all. Media/Format ============ These data are supplied to the Planetary Data System as an online collection of CDF files. CONFIDENCE_LEVEL_NOTE Confidence Level Overview ========================= The data in this data set are thermal plasma parameters derived from HFR spectra using the thermal noise spectroscopy theory. Every data has been reviewed by a scientist to ensure that all data included in this data set is scientifically consistent. When the data can not be provided during the selected intervals, the values are replaced by fill values (FillVal = -1e+31). Review ====== The RPWS HFR QTN data set has been internally reviewed by the Cassini RPWS team prior to release to the PDS. The data set has also been peer reviewed by the PDS. Data Coverage and Quality ========================= All data in the stated interval are included, to the best of our knowledge and attempts to determine completeness. This initial release is consisting of results for each perikrone from the SOI (Saturn Orbit Insertion) to April 2012. The time interval for each data file is in the index_1.0.csv file (in the hfr-qtn-document collection), with the associated revolution number (i.e. orbit number) and the number of data points. Limitations =========== The Quasi Thermal Noise Spectroscopy analysis is using the FuH resonance for the determination of the electron core density. This determination depends on: (1) the ability to identify the resonance among the other lines and noises present in the data at the same time; (2) the operating spectral resolution, which defines the accuracy the the determination of FuH. Concerning the first item, the scientific evaluation step is ensuring that the detected FuH line is not another emission or a spurious detection. The electron core temperature is dependent on the thermal plateau level below the Upper hybrid resonance peak. The accuracy of the temperature determination depends on the integration time (the longer reducing the statistical noise on the data). The core electron temperature determination is also highly dependent on the shot noise contamination induced by the impact of the charged particles on the antennas (proportional to f^-2). The shot noise is dominant in the lowest part of the HFR frequency band and may artificially increase the minimum QTN level, inducing an overestimate of the core temperature. For this reason, we rejected the spectra where the contribution of the shot noise is larger than 20% of the thermal plateau level below FuH in the provided dataset. The Quality Flag on temperature QF is equal to 1 when the shot noise ratio is lower than 10%, and 0 when the ratio is comprised between 10% and 20%. For best quality data, we recommend to the user to use the data with QF=1. Note that the estimate of the core temperature is dependent on the calibration in V^2/Hz of the RPWS/HFR receiver. Calibration may evolve with time and influence the thermal plateau level. The value of the temperature finally also depends on the absolute flux calibration of the HFR, and thus may change in the future in when a new calibration is available.