Phase calibration approaches for radar interferometry and imaging configurations: equatorial spread F results

Abstract

Abstract. In recent years, more and more radar systems with multiple-receiver antennas are being used to study the atmospheric and ionospheric irregularities with either interferometric and/or imaging configurations. In such systems, one of the major challenges is to know the phase offsets between the different receiver channels. Such phases are intrinsic to the system and are due to different cable lengths, filters, attenuators, amplifiers, antenna impedance, etc. Moreover, such phases change as function of time, on different time scales, depending on the specific installation. In this work, we present three approaches using natural targets (radio stars, meteor-head and meteor trail echoes) that allow either an absolute or relative phase calibration. In addition, we present the results of using an artificial source (radio beacon) for a continuous calibration that complements the previous approaches. These approaches are robust and good alternatives to other approaches, e.g. self-calibration techniques using known data features, or for multiple-receiver configurations constantly changing their receiving elements. In order to show the good performance of the proposed phase calibration techniques, we present new radar imaging results of equatorial spread F (ESF) irregularities. Finally we introduce a new way to represent range-time intensity (RTI) maps color coded with the Doppler information. Such modified map allows the identification and interpretation of geophysical phenomena, previously hidden in conventional RTI maps, e.g. the time and altitude of occurrence of ESF irregularities pinching off from the bottomside and their respective Doppler velocity.

Empirical Phase Calibration for Multistatic Specular Meteor Radars Using a Beamforming Approach

“…Our proposed technique has been motivated by the works of Chau et al () and Holdsworth, Tsutsumi, et al (); that is, we use selected meteor events for a relative phase calibration and the expected angular and altitudinal meteor distributions for an absolute calibration, respectively. For an noncalibrated interferometer, the measured visibility pair ( m , n ) of a meteor can be modeled as follows: where Δ γ mn = γ m − γ n and γ m is the phase offset of receiver antenna m that needs to be calibrated.…”

“…In atmospheric and ionospheric interferometric radars, particularly those operating in the high‐frequency and very high frequency bands (i.e., between 3 and 300 MHz) different procedures have been proposed. For example, the use of localized radio sources is a common practice in large array systems (e.g., Chau et al, , ; Palmer et al, ; Woodman, ). A complete list of procedures used in these radars can be found in Holdsworth, Tsutsumi, et al () and Chau et al ().…”

Auroral ion acoustic wave enhancement observed with a radar interferometer system

“…Calibration of phase offsets introduced in the receiver systems is a crucial step before radar imaging can be achieved (Chau et al, 2008). At high latitudes, satellites transiting the radar beam provide strong backscattering targets which make it possible to estimate the receiver phase offsets and the antenna baselines.…”

Phase calibration of a radar interferometer by means of incoherent scattering

“…Earlier, Sahr [1996] introduced the concepts of closure phase and self‐calibration from radio astronomy to the field of radar imaging. The 2‐D imaging setup that has been used with great success at Jicamarca Radio Observatory [e.g., Hysell , 1996] can be calibrated in several ways: by means of a reference beacon on a nearby hilltop; using known astronomical radio sources; or simply by centering the distribution of scatterers in each baseline observation [ Chau et al , 2008].…”