Cassini/RPWS/HFR-Kronos
Access to Lesia-Meudon data products
Plasma density and temperature with Quasi-Thermal Noise Spectroscopy
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 files 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]):
The total electron density Ne is then obtained as:
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 total electron density Ne is then obtained as:
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 Vmin2 below FuH, given in [2] as a function of the core
temperature Tc and Debye length LD (see Eq. 1 of [2]):
(using S.I. units), Vmin2 in V2/Hz. Here Fv(kL) is the Cassini V-shaped antenna response, with L the single wire length (L ~ 10m),
is the dipole antenna capacitance at low frequencies, with a the wire radius (a ~1.4 cm), and CB is the base capacitance. We then use an iterative method to deduce Tc.
(using S.I. units), Vmin2 in V2/Hz. Here Fv(kL) is the Cassini V-shaped antenna response, with L the single wire length (L ~ 10m),
is the dipole antenna capacitance at low frequencies, with a the wire radius (a ~1.4 cm), and CB is the base capacitance. We then use an iterative method to deduce Tc.
The error on the temperature is determined a posteriori by
estimating the averaged 1-sigma dispersion of the temperature level
during the perikrone.
A full description of the methodology and results can be found in [3]
References
[1] Dougherty et al. 2004. [link]
[2] Moncuquet et al, 2005. [link]
[3] Schippers et al, 2013. [link]
[2] Moncuquet et al, 2005. [link]
[3] Schippers et al, 2013. [link]