Flexible Prior Model, four dimensional electron density, Total Electron Content (TEC) and applications to radar tracking in real time

Ionospheric error correction is an important aspect of radar tracking. The ionosphere is usually not considered an issue at higher frequencies because of the dispersive nature of its effects on radar metrics accuracy. Although there is some discussion about potential ionospheric effects even at X band and above, it is well known that ionospheric effects can be considerably disruptive at UHF and VHF. Consequently, there is a need to assess ionospheric effects for radars running at these frequencies and if necessary to develop mitigation techniques and algorithms that will eliminate and/or minimize these effects. Several techniques were developed to accomplish the above stated purposes. These techniques include: real time error correction using the Global Positioning System (GPS) such as the wide area augmentation system (WAAS) used by the Federal Aviation Administration (FAA), or real time error correction using the two-frequency measurement systems used by the long range tracking and instrumentation radar (ALTAIR) radar at the Kwajalein missile range (KMR). It is known that the errors in radar metrics accuracy are directly related to the radar range and phase delays, which are in turn related to the total electron content (TEC) of the ionosphere along the radar line of sight. In this paper, a new method will be presented which will discuss real time ionospheric error correction using a flexible prior model based on state of the art prior models such as the parameterized ionospheric model (PIM). The proposed method is based on both, a technique commonly known as ionospheric tomography and a prior model that is flexible as opposed to the traditional fixed Bayesian model, which provides means for evaluating ionospheric effects along the radar lines of sight of interest. The technique also allows for a systematic means of generating monthly mean TEC maps. In addition, the technique allows for first order TEC solutions, in the case where radar resource is an issue, and f- or higher order TEC solutions, when radar resources are readily available. This new technique´s ultimate goal is to create a four-dimensional adaptive ionospheric electron density reconstruction system that makes it possible to generate real-time TEC maps. Such maps would be of significant utility in predicting and correcting the impact of TEC gradients and irregularities on radio and radar waves.