Quantitative measurements with wide-beam riometers

摘要

Relative Ionospheric opacity meters (Riometers) have provided information on the state of the lower ionosphere for decades, however only imaging riometers have received detailed attention in recent years. The simpler and more common riometers with wide opening angles pose problems which do not occur in imaging riometers with their narrow beams and a careful analysis is required when one attempts to make comparisons between the two types or when trying to simulate riometer absorption. A procedure to reduce apparent absorption to what one should expect from a vertical pencil-beam riometer is given as well as an estimate of the effective opening angle based on the variation of the quiet day curve. By using a 30 MHz digital map of the sky noise, it is quantitatively demonstrated that the absorption measured with a wide beam antenna is larger than using a vertical pencil-beam antenna, and that the difference between maximum and minimum received power increases with decreasing antenna beam width. Finally, a comparison of observed riometer absorption and simulated absorption using measured electron density profiles is made.