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

摘要

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 RAD 1 in SEP (X) mode observations against TNR allows us to calculate the relative receiver gain GRi = 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 GR2Gy = 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 1( 2/3)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.