On the phase biases of multiple‐frequency radar returns of mesosphere‐stratosphere‐troposphere radar

Abstract

[1] The frequency domain interferometry (FDI) technique uses two or more frequencies to measure the positions and thicknesses of the atmospheric thin layers embedded in the radar volume, in which the cross-correlation analyses of the radar echoes for the pairs of carrier frequencies are performed and the resultant amplitudes and phases (FDI phase) are both employed. However, in light of the possibility that the characteristics of radar system, mean refractivity gradient, and other factors that would significantly affect the FDI phase, calibration of the FDI phase is required to improve the measurement. In this study we employed three methods in measuring the phase bias in the FDI observation using the Chung-Li VHF radar; namely, (1) histogram of the FDI phases, (2) relationship between echo power and FDI phase, and (3) the FDI phase of aircraft. Both methods 1 and 2 are based on the range weighting effect on the radar echoes returned from the atmospheric scatterers; however, the first produced smaller FDI phase bias than the second. To examine such discrepancy in the results of methods 1 and 2, method 3 was exploited and provided more consistent values of phase biases with those of method 2. Considering that the radar echoes reflected from aircrafts are not related to uncertain conditions of the atmosphere such as mean reflectivity gradients and statistical characteristics, the results of methods 2 and 3 may be more reliable. Besides, the first two methods demonstrated that the FDI phase bias was quasi-linearly dependent on the separation of frequency pair, which not only consolidates the existence of the FDI phase bias but also indicates that a systematic phase compensation for the FDI analysis is possible. For example, considering 0.1-, 0.4-, and 0.8-ms time delays of signals for the returns of 1-, 2-, and 4-ms pulse lengths, respectively, the FDI phase biases can be removed effectively. Same methods and procedures can be applied to other radar systems.

Measurement of Range-Weighting Function for Range Imaging of VHF Atmospheric Radars Using Range Oversampling

“…The two-way RWF is represented by W 2 (r). The role of the oversampled range gates in this study is equivalent to that of the partly overlapped radar beams conducted by Chen and Furumoto (2011). (1) for the oversampled range gates in Fig.…”

“…In the practical process of RIM, the RWF suitable for recovering the brightness may change with SNR, as first examined by Chen and Zecha (2009). For our present study, we applied again the estimator of mean-square error used by Chen and Zecha (2009):…”

“…Among the studies of RIM and CRI, Zecha (2009) andChen et al (2009) raised the concept of effective RWF for RIM; following this, Chen and Furumoto (2011) proposed the effective beam-weighting function (BWF) for CRI. These works were carried out under the consideration that the estimated brightness is weighted by the RWF and BWF; a further examination of this subject was made by Chen et al (2011) for the threedimensional radar imaging.…”

“…Another goal of this study is to develop an approach for the measurement of RWF from the observed RIM data, similar to that made by Chen and Furumoto (2011) for CRI. To verify this assertion is one goal of this study.…”

New Observations by Wind Profiling Radars

“…In a practical manner, only the relative phase differences among the frequencies are necessary to correct the effects of system delay. Therefore, the correction is able to be attained by calculating the phase term of cross correlation between the two time series of received signals measured at different frequencies (Chen, 2004). Measurement results of phase correction using the clear-air echoes are shown by Chen et al ( , 2010 and .…”