A global radio frequency noise survey as observed by the FORTE satellite at 800 km altitude

Abstract

We present a global radio frequency noise survey observed from the Fast on‐Orbit Recording of Transient Events (FORTE) satellite at 800 km altitude. This is a survey of squared amplitudes (R2) in 44 frequency subbands spaced by 0.5 MHz centered at 38 MHz (“low band”) and 44 subbands spaced by 0.5 MHz centered at 130 MHz (“high band”). We define 13 geographic regions and analyze signal‐free regions of event data, generated from November 1997 to December 1999, that we assume are representative of the noise of interest (discussion provided). Because this noise distribution is nonstationary, we use cross validation to sample the distribution across time. Summary statistics presented for R2 include the mean, median, percentiles, and fractions exceeding thresholds in each of the 44 subbands for the low‐ and high‐frequency bands in each of the geographic regions. Fractions exceeding thresholds are particularly relevant to multiband signal detection. In the low band the R2 versus frequency plot for each of the 13 regions has peaks in the mean and median at approximately 35 MHz; many regions have peaks at approximately 28 and 45 MHz. The high‐band spectral plots are generally slightly smoother with less dramatic peaks than in the low band. The values of 10 × log10(R2) range from approximately −110 to −70 for both the low band and high band and are generally slightly larger in the low band. The continental United States (CONUS) region low band is notably higher, with values ranging from −105 to −62. Several future satellite projects involving triggered radio frequency broadband signal recordings can benefit from a realistic trigger‐noise survey such as done here.