Backscatter ionogram inversion

A backscatter ionogram, BSI, is a plot showing the group path or time delay against operating frequency when using ground-based swept frequency radar. In the case of ground backscatter, the received signals are reflected from distant locations on the Earth's surface. The ionosphere is the medium through which both the transmitted and received signals traverse. A backscatter ionogram contains useful information regarding the state of the ionosphere at the time and over the range of the returned signal, which could be a few thousand kilometers from the transmitter/receiver location. Backscatter ionograms differ from the more conventional vertical incidence ionograms, where the received signals are reflected from a region of the ionosphere vertically above the sounder location. Methods of inverting backscatter ionograms to obtain ionospheric profiles offer an important means of remote sensing the distant ionosphere and regions in which land and sea scatter occur. Thus, backscatter ionograms can play an important role in the frequency management systems of over-the-horizon radar.