Automated Scaling Software for Oblique Incidence Ionograms

ABSTRACT:The objective of this solicitation is to develop real-time automatic scaling software for oblique ionograms (OIs). The NWRA team has developed an extensive HF propagation computational tool set, which includes a capability called APEx (Automated Point Extraction) for automatically finding vertical ionogram (VI) traces within an ionogram image. APEx does not require pre-separation of the O- and X-modes of the ionogram (although this is beneficial). We will extend Apex to OIs. We show in this proposal that APEx can already be used to select OI trace points, but we will refine APEx substantially during the proposed effort. Using recently-developed mathematical concepts of sparsity and fractional norms, we will develop a robust method for selecting the desired trace data and determining whether a given point is O or X while reducing selection of noise/interference data. A selected OI trace could be converted to an approximately equivalent VI using the laws of virtual geometry (VG) and inverted to an electron density profile, but this is an unnecessarily inaccurate method. We will instead assimilate the OI trace data directly into NWRAs assimilative ionosphere model, GPSII (GPS Ionospheric Inversion). This approach allows for ionospheric horizontal gradients that would be lost in the VG approach.BENEFIT:An automated system for finding oblique ionogram trace points will allow for real time assimilation of potentially dense networks of ionosondes. The Australian DSTO has already fielded such a network, the Dense Integrated Network of Ionospheric Sensors (DINIS), for defining the propagation environment of their OTH radar system, JORN. A similar networked sounding system has been proposed for the US Next Generation OTH Radar (NGOTHR). Making best use of the ionograms provided by an ionospheric sounding network to improve the geolocation accuracy of NGOTHR will require a direct 3D ionospheric data assimilation algorithm like NWRAs GPS Ionospheric Inversion (GPSII). For GPSII to function without a human in the loop, as will be necessary for the throughput required of NGOTHR, automated trace extraction will be required. This capability will also benefit the intelligence community. A limitation of HF geolocation of emitters in denied territories is the inability to measure the ionosphere in the denied region using vertical ionosondes. However, it is often completely reasonable to propagate over a denied region using oblique-incidence HF paths, that is, oblique ionograms. GPSII is already being evaluated in the IARPA HFGeo program and has proven to provide unparalleled accuracy in accounting for the signal deflections caused by medium-scale traveling ionospheric disturbances (TIDs). A reliable OI autoscaling capability will extend the benefit of GPSII to HFGeo in denied territories.