Determining riometer quiet day curves 1. The matrix method

Abstract

[1] A number of methods have been proposed for the determination of quiet day curves of riometer recordings of cosmic radio noise in polar regions. Most of these methods are based on the distribution of the recorded intensities, in a given siderial time period, over a number of consecutive days. The method proposed in this paper is based on the filtering, using a low-pass filter in the Fourier domain, of a discrete two-dimensional function or matrix. The two dimensions of the matrix are siderial time and day number, with each row of the matrix representing one siderial day. With a low-pass filter the low frequency Fourier coefficients are retained while the high frequency Fourier coefficients are discarded. The highest Fourier coefficient that is retained is the cutoff frequency of the filter. The proposed method was compared to two existing methods using data obtained from a single broad beam antenna. It was found that the proposed method is less sensitive to noise than the existing methods.INDEX TERMS: 6964 Radio Science: Radio wave propagation; 6982 Radio Science: Tomography and imaging; 6974 Radio Science: Signal processing; Citation: Drevin, G. R., and P. H. Stoker, Determining riometer quiet day curves 1. The matrix method,

Determining riometer quiet day curves 2. Derivation of filter cutoff frequencies

“…The data used in this study were recorded during 1983 at Sanae using La Jolla fast response solid state riometers at frequencies of 30 and 51.4 MHz. The noise and gaps were removed from this data, after which the data were resampled into 512 intervals per day and translated to siderial time [ Drevin and Stoker, 2003]. The resulting data set is hereafter referred to as the smooth‐data set.…”

“…The matrix method for the determination of riometer quiet day curves, proposed by Drevin and Stoker [2003], is based on the filtering of a discrete two‐dimensional function or matrix representation of the riometer data. This matrix's dimensions are siderial time and day number, with each row of the matrix representing one siderial day.…”