D-Region Ionosphere Inferred Maps of Electron-density (DRIIME)

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The award to Georgia Tech University would support an initiative to establish a long-term ionospheric plasma spatial mapping capability for the altitudes of 60-90 km with Very Low Frequency (VLF, 3-30 kHz, 33-333 μs period) radio receivers. While spatial maps of the upper atmosphere plasma distribution for altitudes above 250 km have been obtained through remote sensing using GPS measurements of total electron content, no such capability currently exists for this lower ionospheric plasma region. VLF remote sensing has long been viewed as the most promising technique for remote sensing in this region, but several factors have made it very difficult to go from VLF measurements to ionospheric maps. However, two recent advances in ionospheric diagnostics have now enabled this mapping to be achieved. This award would address three key goals for the work: the formulation of a unified map determination method using a fusion of two VLF remote sensing advances, quantification of the temporal and spatial resolution achieved, and validation through checking for internal self-consistency combined with comparison with results of external HF absorption analysis. These maps would be analyzed and the raw and processed data products made public expanding the possible scientific impact to other fields. The research supported by this award would represent progress toward achieving an accurate model of HF absorption useful for the aviation industry. As part of this award broader educational outreach, a set of tutorials that would enable scientists in related fields to understand and use the public datasets would be developed and made available as part of the public release of data. Summer undergraduate interns from underrepresented groups would participate in this award research effort using an established Georgia Tech program designed to achieve diversity and inclusion.VLF signals reflect efficiently from this plasma region (known as the D-region) but also VLF signals detected at a distance from a source change as ionospheric conditions change. While this principle has been known for decades, translating measurements to plasma density estimates is more difficult. There are two major sources of VLF waves that can be used for this form of remote sensing: VLF transmitters and radio atmospherics (sferics) emitted by global lightning. Two major advances, one for each type of VLF source, solve many of these problems. The award research plan would merge VLF transmitters and sferics in a single technique. A novel way of validating VLF remote sensing results with independent measurements would be introduced. This development would avoid a longstanding hurdle for VLF remote sensing, which is the lack of direct measurements of plasma content for comparisons with results. The new capability would allow direct observations of not only the ambient ionospheric conditions including diurnal and seasonal changes, but several types of ionospheric disturbances like Early VLF events and effects relating to atmospheric gravity and acoustic waves.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.