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.
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