Application of MaxEnt Optimal Imaging to the Passive Manastash Ridge Radar

(MRR) is a passive VHF radar network located in the Pacific Northwest. The radar leverages commercial FM radio broadcasts (∼100 MHz) for illumination and low-cost commercial software radio components to sample the RF signal. Common targets include Bragg scatter off E-region turbulence, meteor wakes, and local aircraft [4]. In ordinary operation the radar samples two signals with receivers separated by 150 km. A single an-tenna at the University of Washington (UW) records the FM waveform from local commercial transmitters. The scattered signal is sampled at Manastash Ridge Observatory (MRO). These two signals are combined to produce range-doppler images through a cross-ambiguity calculation. This mode has run nearly contin-uously for seven years, producing new data every four minutes in the standard surveillance mode. During magnetospheric storms, the system can absorb several days of nearly continuous samples. The real-time surveillance mode is limited by available network bandwidth at the MRO site; the underlying hardware limitation is actually the amount of storage available at each site. In 2003, the first passive interferometer revealed fine-scale (0.1 degrees, or 2km at 1000km range) transverse resolution of E-region turbulence [3]. While the physical geometry constrains the ionospheric targets to select portions of the field of view at MRO, completely unambiguous direction of arrival estimation of these targets was impossible because th