Specification of Nighttime Ionospheric Irregularities: Occurrence, Spatial, and Dynamic Properties

Office of Naval Research
Jonathan J. Makela (PI)
Jan 2009-Dec 2011

In this project, we will develop automated analysis algorithms to extract pertinent spatio-temporal properties of ionospheric structures from an imaging database collected over the previous solar cycle. Effects on trans-ionospheric radiowave propagation will be studied using collocated radio (GPS) measurements. A database of structure occurrence, drift velocity, widths, and altitudes as a function of longitude, season, and solar cycle will be created and analyzed. The analysis routines will be developed such that they can be run in near real-time as part of an ionospheric structure specification network.

Studying nighttime ionospheric irregularity processes at low latitudes has become a major focus of the space weather and Aeronomy communities over the past decade. This is due to the recent proliferation of space-based assets, such as satellite communication and navigation systems, and our increasing reliance on such systems, both for civilian and military purposes. Irregularities in the ionosphere can cause these systems to become temporarily unreliable or unusable. Current specification methodologies rely on climatology-based metrics, such as the known longitudinal, seasonal and solar-cycle dependence of these structures at low-latitudes. These climatologies have been developed over decades of data collection, primarily based on scintillation measurements from radio receivers (e.g., Aarons et al., 1993, Makela et al., 2004) or from in-situ satellite measurements (e.g., Gentile et al., 2006). However, little attention has been given to the spatio-temporal properties of the individual irregularity regions, which have a pronounced affect on which transmitter-receiver channels are available/unavailable. This lack of attention is primarily driven by the available datasets and the information that can be extracted from them. For example, ground-based radio receivers measure integrated effects of the irregularities along a single line-of-site to a given satellite transmitter. Information on the spatial extent of the scintillation-causing irregularities cannot easily be gleaned from such point measurements, as the structures can be extended in several hundreds of kilometers in the meridional direction and tens of kilometers in the zonal direction. Arrays of radio receivers, such as dual-frequency GPS receivers, can be used to create a map of depletion structure (Lee et al., 2008), but there are very few suitably dense arrays in the world currently operating and the obtainable spatial/temporal resolutions obtained by such techniques is limited.

Imaging is the only observing modality that can easily provide high-resolution measurements of the spatio-dyamical properties of two-dimensional (latitude/longitude) ionospheric structures. Using an all-sky imaging system, such as the Portable Ionospheric Camera And Small-Scale Observatory (PICASSO) developed at the Naval Research Laboratory, observations of nighttime ionospheric structures can be obtained at spatial resolutions on the order of 1 km and temporal resolutions of 90 s over a 1000 km × 1000 km area. Higher resolution images (sub-km spatial resolution) can be obtained over smaller areas using a modified PICASSO system with a smaller field of view. Images obtained from these, and similar, systems show incredible spatio-temporal dynamics as ionospheric structures develop, drift, and decay over time. These dynamics have a direct affect on which transmitter-receiver links are available at a given time. Thus, a better understanding and specification of these properties will lead to more robust communication schemes in both the civilian and military regimes.

Over the past seven years, we have amassed a large dataset of optical and collocated radio observations of ionospheric irregularities from several locations. In the proposed work, we would develop automated analysis algorithms to extract pertinent spatio-temporal properties of ionospheric structures from the imaging database. Effects on trans-ionospheric radiowave propagation would be studied using the collocated radio (GPS) measurements. A database of structure occurrence, drift velocity, widths, and altitudes as a function of longitude, season, and solar cycle would be created and analyzed. The analysis routines would be developed such that they could be run in near real-time as part of an ionospheric structure specification network. In addition, if optional funding were provided, we would conduct a ground campaign in New Mexico to study the linkage between lightning, gravity waves in the mesosphere and the occurrence of mid-latitude structure in the ionosphere. This would provide valuable insight into the linkage of different atmospheric regions and the upward coupling of energy which is believed to have a significant impact on the ionosphere.