Cassini/RPWS/HFR-Kronos
Access to Lesia-Meudon data products
Plasma density and temperature with Quasi-Thermal Noise Spectroscopy
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
"NaN" (Not a Number) flags.
Limitations
The Quasi Thermal Noise Spectroscopy analysis is using the FuH
resonance for the determination of the electron core density. This
determination depends on:
- the ability to identify the resonance among the other lines and noises present in the data at the same time;
- 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 ability to identify the resonance among the other lines and noises present in the data at the same time;
- 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 V2/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.