Average received signal power after two‐way propagation through ionized turbulence

Abstract

Abstract.In this paper we consider propagation through a structured ionosphere separating a monostatic or bistatic radar and its target. A new analytic calculation of the correlation function of the received, demodulated signal is presented. This result is a function of the locations of the transmit and receive apertures and of time during the duration of the received pulse. Strong scattering is assumed where the one-way scintillation index is unity; under this assumption the parabolic wave equation can be solved using the quadratic approximation for the phase structure-function; this facilitates tractable expressions for the mutual coherence function (MCF) for both one-and two-way propagation. A new expression is given for the two-position, two-time, two-frequency MCF for spherical wave propagation that allows simultaneous description of all effects of the ionospheric propagation channel (or transmission medium) on a propagating radar signal.To obtain useful and tractable results, the transmitted signal is assumed to be a chirp (linear FM) pulse, a waveform used by most long-range defense radars. The result for the correlation function of the received signal is a function of the basic parameters that describe wave propagation through the ionospheric structure, including the channel decorrelation distance, decorrelation time, and coherence bandwidth. Both the two-way enhancement in average power and aperture averaging effects are explicitly included in this derivation, and new results are presented that relate these effects to the characteristics of the propagation channel. The results are useful for propagation under conditions of saturated scintillation, for example HF through UHF radar in the natural equatorial environment and HF through gigahertz-band radars that are required to operate in a disturbed propagation environment (i.e., in chemical releases or nuclear detonations).

Forecasting the Appearance and Evolution of Ionospheric Irregularities and Structures: Their Effects on AF Systems

“…The second part concerns the interactions between the resident space object (in our case, a calibration sphere) and the radar pulse arriving at the target to produce the scattered wave. For the current example, we assume that the target is a frequency-flat point scatterer with unity reflectivity located at a horizontal distance x 1 [Knepp and Brown, 1997]. Under this assumption, the complex amplitude of the scattered wave…”

TEC retrieval from spaceborne SAR data and its applications

“…In fact, the SAR signal traverses the turbulent ionosphere twice; a two‐way path delay due to multiple scattering is therefore needed. Under the Gaussian approximation in saturated strong fluctuations, the relation between two‐ and one‐way path delays is derived by Knepp and Brown [] based on the power response function, i.e., , where t s 2 is the two‐way path delay.…”

Simulating the effects of scintillation on transionospheric signals with a two‐way phase screen constructed from ALTAIR phase‐derived TEC

“…The second part concerns the interactions between the resident space object (in our case, a calibration sphere) and the radar pulse arriving at the target to produce the scattered wave. For the current example, we assume that the target is a frequency‐flat point scatterer with unity reflectivity located at a horizontal distance x 1 [ Knepp and Brown , 1997]. Under this assumption, the complex amplitude of the scattered wave A s ( x , z ) becomes where δ ( x ) is the Kronecker delta function.…”