Scientific investigation of plasma turbulence in the lower ionosphere relies heavily upon VHF and UHF radar remote sensing. The neutral atmosphere is too thin to loft balloons above 40 km, and too thick for durable satellites below about 200 km. The entire in situ sounding rocket data set for the lower ionosphere probably does not exceed 2-h duration. This chapter is especially concerned with the technique of 'coherent scatter radar' which refers to the use of moderately sensitive VHF and UHF systems that detect scatter of radio waves from large amplitude fluctuations in the plasma density. This is in contrast to the much more sensitive 'incoherent scatter radar' technique, which refers to VHF and UHF systems that detect the scatter of radio waves from the thermal fluctuations in the plasma medium. The underlying radar waveforms and receiver systems can be quite similar, as both targets are volume scatterers with similar spatial and temporal scales. Both radar systems coherently detect the scatter of radio waves from a large volume of incoherent scatterers. From the point of view of the radar performance, the main difference is the level of sensitivity required; the scattering cross section of thermal scatter is 40-70 dB smaller than that of turbulent fluctuations. This chapter describes the Manastash ridge radar, which is a passive, bistatic VHF (100 MHz) radar performing a 'coherent scatter' function.

Chapter Contents:

• 7.1 Introduction
• 7.2 Field-Aligned Irregularities
• 7.3 Detection of FAI with Passive Radar
• 7.4 System Engineering Issues
• 7.5 Future Plans
• Acknowledgements
• References

Inspec keywords: ionospheric electromagnetic wave propagation; radiowave propagation; remote sensing by radar; ionospheric techniques; passive radar; radar theory; electromagnetic wave scattering

Other keywords: UHF system; coherent scatter function; bistatic radar; incoherent scatter radar; ionospheric measurements; lower ionosphere; frequency 100 MHz; radio wave scatter; VHF radar; Manastash ridge radar; plasma density; plasma turbulence; neutral atmosphere; radar remote sensing; passive radar; VHF system

Subjects: Radar theory; Radiowave propagation; Atmospheric, ionospheric and magnetospheric techniques and equipment; Instrumentation and techniques for aeronomy, space physics, and cosmic rays; Radar equipment, systems and applications; Ionospheric electromagnetic wave propagation