Abstract
AbstractElevation angles of backscattered signals are calculated at the Super Dual Auroral Radar Network (SuperDARN) high‐frequency radars using interferometric techniques. These elevation angles make it possible to estimate the geographic location of the scattering point, an essential piece of information for many ionospheric studies. One of the most difficult parameters to measure is the effective time delay caused by the difference in the electrical path length that connects the main array and the interferometer arrays to the correlator (δtc). This time delay causes a bias in the measured difference in the signal phase, also known as a phase bias. Phase calibration is difficult due to unknown physical attributes of the hardware and the remote location of many radars. This leads to the possibility of sudden external changes, slow temporal drift, and a dependence on transmission frequency. However, it is possible to estimate δtc using the radar observations themselves. This article presents a method for estimating δtc using backscatter with a known location, such as backscatter from artificially generated irregularities, meteor echoes, or distinct groundscatter, which incorporates the uncertainty in the observations and may be used autonomously. Applying the estimated δtc is shown to improve elevation angle uncertainties at one of the SuperDARN radars from their current potential tens of degrees to less than a degree.
Highlights
Coherent-scatter high-frequency (HF) radars work by sending a series of radio pulses out toward a scattering region and measuring the time it takes for the backscattered signal to return, the difference in phase between the transmitted and received signal, and the strength of the received signal
Groundscatter can be observed when the radio signal is refracted down to the ground. Both ionospheric backscatter and groundscatter are observed by the Super Dual Auroral Radar Network (SuperDARN) [Greenwald et al, 1995; Chisham et al, 2007], which is made up of coherent-scatter HF radars that were deployed to observe the middle- and high-latitude ionosphere over the northern and southern poles
This paper presents a method of estimating δtc for HF radars that can be applied routinely or retrospectively to data sets that fulfill certain requirements
Summary
Coherent-scatter high-frequency (HF) radars work by sending a series of radio pulses out toward a scattering region and measuring the time it takes for the backscattered signal to return, the difference in phase between the transmitted and received signal, and the strength of the received signal. These errors can be caused by multipath propagation, self-clutter from the multipulse signaling method [Reimer and Hussey, 2015], uncertainty in the azimuth angle caused by the possibility of signals returning from both in front of and behind the main radar array [Milan et al, 1997a], and phase bias (δtc), which results from a difference in the electrical paths that connect the main and interferometer arrays to the radar correlator [Baker and Greenwald, 1988] Most of these sources of error are either corrected in the standard SuperDARN data analysis or can be corrected as a secondary processing step [Burrell et al, 2015].
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