Automatic detection of the electron density from the WHISPER instrument onboard CLUSTER II

Description

The Waves of HIgh frequency and Sounder for Probing Electron density by Relaxation(WHISPER) instrument, is part of the Wave Experiment Consortium (WEC) of the CLUSTER IImission. The instrument consists of a receiver, a transmitter, and a wave spectrumanalyzer. It delivers active (when in sounding mode) and natural electric field spectra. Thecharacteristic signature of waves indicates the nature of the ambient plasma regime and, combinedwith the spacecraft position, reveals the different magnetosphere boundaries and regions. Thethermal electron density can be deduced from the characteristics of natural waves in natural modeand from the resonances triggered in sounding mode, giving access to a key parameter of scientificinterest and major driver for the calibration of particles instrument.Until recently, the electron density derivation required a manual time/frequency domaininitialization of the search algorithms, based upon visual inspection of WHISPER active and naturalspectrograms and other datasets from different instruments onboard CLUSTER.To automate this process, knowledge of the region (plasma regime) is highly desirable. A Multi-Layer Perceptron model has been implemented for this purpose. For each detected region, a GRU,recurrent network model combined with an ad-hoc algorithm is then used to determine the electrondensity from WHISPER active spectra. These models have been trained using the electron densitypreviously derived from various semi-automatic algorithms and manually validated, resulting in anaccuracy up to 98% in some plasma regions. A production pipeline based on these models has beenimplemented to routinely derive electron density, reducing human intervention up to 10 times. Workis currently ongoing to create some models to process natural measurements where the data volumeis much higher and the validation process more complex. These models of electron densityautomated determination will be useful for future other space missions.

Abstract

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