Radar Sounding Through the Earth's Ionosphere at 45 MHz

• Published in: IEEE transactions on geoscience and remote sensing Vol. 55; no. 10; pp. 5833 - 5842
• Main Authors: Freeman, Anthony, Xiaoqing Pi, Heggy, Essam
• Format: Journal Article
• Language: English
• Published: New York IEEE 01.10.2017; The Institute of Electrical and Electronics Engineers, Inc. (IEEE)
• Subjects: Airborne radar; Aircraft components; Aquifers; Aridity; Deserts; Earth; Earth orbit; Earth orbits; Electromagnetic properties; Glacial deposits; Glaciation; Ground penetrating radar; Ice; Ice sheets; Ionosphere; Ionospheric propagation; Layering; Mars; Radar; radar sounding; Remote sensing; Sounding; Soundings; Spaceborne radar; very high frequency (VHF); Volcanoes; Wavelength; Wavelengths
• ISSN: 0196-2892; 1558-0644
• DOI: 10.1109/TGRS.2017.2715838

Radar sounding from aircraft or ground-coupled radars has long provided scientists with a powerful technique to sound through ice layers to retrieve local depth and layering structure. More recently, it has been used to detect shallow aquifers in warm, dry, and desert regions. At Mars, a long-wavelength radar sounding from low orbit altitudes has produced global maps that reveal the presence of ice layering at all latitudes and glacial deposits on the flanks of volcanoes. Until now, sounding from the earth orbit at wavelengths long enough to penetrate ice sheets and arid sand was thought to be infeasible, because of the electromagnetic properties of the ionosphere. In this paper, we show that a radar sounding at frequencies as low as 45 MHz is, in fact, theoretically possible under viewing conditions that occur often enough to be practical. This conclusion opens up a previously unutilized portion of the electromagnetic spectrum for large-scale, spaceborne remote sensing of subsurface features on the earth.