Direct Antenna Impedance Measurement for Quantitative AC Electric Field Measurement by Arase. Issue 6 (14th June 2021)

• Record Type: Journal Article
• Authors: Matsuda, S.; Kojima, H.; Kasahara, Y.; Kasaba, Y.; Kumamoto, A.; Tsuchiya, F.; Matsuoka, A.; Miyoshi, Y.; Shinohara, I.
• Is Part Of: Journal of geophysical research. Volume 126:Issue 6(2021)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2021-06-14
• Subjects: antenna impedance -- Arase satellite -- electric field measurement -- inner magnetosphere -- plasma waves; Magnetospheric physics -- Periodicals; Space environment -- Periodicals; Cosmic physics -- Periodicals; Planets -- Atmospheres -- Periodicals; Heliosphere (Astrophysics) -- Periodicals; Geophysics -- Periodicals; 523.01
• DOI: 10.1029/2021JA029111
• Languages: English
• ISSNs: 2169-9380

Abstract

Abstract: We developed an in‐situ direct measurement technique for the electric field antenna impedance using onboard signal processing. Antenna impedance is an important parameter for observed electric field calibration. Because it changes depending on local plasma parameters, in‐situ measurements along the orbit are essential for obtaining precise electric field calibration. We installed the onboard signal calibration function (SWCAL) as a part of the onboard software of the plasma wave experiment (PWE) aboard Arase and performed more than 5, 500 measurements in the inner magnetosphere from March 2017 to March 2020. The measured the antenna capacitance along the orbit of Arase, which is important for AC electric field calibration. We found that the measured antenna capacitance varies between 70 and 160 pF depending on the ambient electron density. Further, the effects of the antenna impedance on the AC electric field calibration were evaluated. Results indicated that the observed electric field data include ambiguity of up to 7.8 dB and 17° in the main target frequency range of the waveform capture/onboard frequency analyzer of PWE. This ambiguity can be calibrated by considering the real antenna impedance effects measured using SWCAL. Plain Language Summary: We measure the electric field using wire‐probe antennas aboard the spacecraft. To measure the pure electric field component of the natural plasma waves, we must discuss the effect of the antenna impedance. The plasma is coupled to the antenna via sheath resistance and capacitance formed around the antenna surface. In this study, we developed an in‐situ direct measurement technique for the electric field antenna impedance using onboard signal processing. We installed our technique at Arase and performed over 5, 500 measurements in the inner magnetosphere. We successfully obtained clear variation in the measured antenna impedance as a function of ambient electron density. The measured results are helpful for the quantitative evaluation of an observed electric field, particularly for multipoint measurement studies and wave‐particle interaction analysis in the inner magnetosphere. Key Points: We developed an in‐situ and direct antenna impedance measurement technique for electric field antennas aboard Arase We successfully measured the variation in the antenna capacitance along the orbit of Arase as a function of ambient electron density In the main frequency range of waveform capture/onboard frequency analyzer, the ambiguity of up to 7.8 dB and 17° can be calibrated by considering the antenna impedance