Prediction of background levels for the Wind WAVES instrument and implications for the galactic background radiation

Abstract

[1] We investigate and predict the observed background levels for the TNR, RAD1, and RAD2 receivers when connected to the X, Y, and Z antennas of the WAVES instrument on the spacecraft Wind. The receivers are connected to either a single antenna, in "SEP" mode, or a combination of antennas, in "SUM" mode. With the TNR receiver in SEP (X) mode, the predicted backgrounds agree to within 20% when modeled using a two component model for the quasi-thermal plasma noise (QTN). Calibrating the RAD1 in SEP (X) mode observations against TNR allows us to calculate the relative receiver gain G R1 = 1.43 ± 0.18. Using the RAD1 data in SUM (X+Z) mode, the ratio of antenna gains is found to be R = 6.5, in agreement with preflight measurements. Observed differences between the SEP (X) and SUM (X+Z) modes are explained for the first time, and the predicted levels of QTN and galactic background are found to agree to within 20%. RAD2 is also calibrated against RAD1 and TNR, yielding a total gain G R2 G y = 2.5 ± 0.3. Differences between the predicted and observed galactic background spectra are used to estimate the effective antenna lengths for the X and Y antennas, which are found to be between the physical monopole antenna length L and the Hansen (1981) prediction of ffiffiffiffiffiffiffiffiffiffiffi ð2=3Þ p L. The analyses are consistent with the Novaco and Brown (1978) galactic background model, which decreases much faster than that of Cane (1979). Our model background spectrum is useful for theory-data comparisons of type II and III bursts.

Type II solar radio bursts: Modeling and extraction of shock parameters

“…The background model of Hillan et al [2010, Figure 13] is used to predict B ( f ) as a function of frequency (in W m −2 Hz −1 ) over the entire frequency range of the Wind/WAVES instrument (4‐13825 kHz [ Bougeret et al , 1995]). This model includes contributions from galactic background radiation, dominant at high frequencies above around 300 kHz, local quasi‐thermal plasma noise, dominant at low frequencies below around 300 kHz, and receiver noise.…”

“…The channel frequency spacing varies with the three receivers that span the Wind/WAVES frequency range. However, in the range where much of the observed type II emission occurs (typically ≈ 20 kHz − 1 MHz), the frequency spacing is normally no greater than 4 kHz [ Bougeret et al , 1995; Hillan et al , 2010]. We convert the flux of the dynamic spectrum into a relative decibel scale using where T B ( t , f ) is the dynamic spectrum in relative flux units (dB).…”

Type II solar radio bursts: 2. Detailed comparison of theory with observations

“…(A factor of 10 in the factor ( O ( t , f ) + B ( t , f ))/ B ( t , f ) then corresponds to a difference of 10 dB in DB O ( t , f ).) A model for the WAVES instrument's observed background, including galactic background radiation and quasithermal plasma noise from the solar wind plasma, is presented in Hillan et al [2010] and used here. The dynamic spectra DB O ( t , f ) plotted in Figure 2 are all measured in dB relative to the observed radio and instrument background as per .…”

“…However, this analysis was not fully quantitative and lacked a comprehensive model of the observed satellite background to be incorporated into theoretical spectra for detailed comparisons between theory and observation. A recent model by Hillan et al [2010] of the background observed by the WAVES instrument onboard the spacecraft Wind allows us to directly compare the predicted type II spectra with spacecraft observations and to quantitatively investigate the agreement between theory and observation.…”

“…This paper aims to: (i) Combine the model of Hillan et al [2010] for the instrumental and natural background signals observable at 1 AU with the Wind/WAVES instrument, the type II theory [ Knock et al , 2001; Cairns and Knock , 2006] and the solar wind model of Florens et al [2007] into a comprehensive theory for type II bursts. (ii) Perform detailed comparisons of theory and observations using analyses based on cross‐correlation and a normalized deviation parameter.…”