中壢特高頻雷達系統初始相位偏差估計與應用;Estimation and application of phase offsets of Chungli VHF radar system

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Title:	中壢特高頻雷達系統初始相位偏差估計與應用;Estimation and application of phase offsets of Chungli VHF radar system
Authors:	林廷翰;Lin, Ting-Han
Contributors:	太空科學研究所
Keywords:	中壢特高頻雷達;同相散射雷達;空間域雷達干涉法;系統初始相位偏差;相位校正;散塊E層;場沿電漿不規則體;廣播式自動相關監視系統;風切理論;Chungli VHF Radar;Coherent scatter radar;Spatial interferometry;System phase offset;Phase calibration;Sporadic E layer;Field-aligned irregularities;ADS-B system;Windshear theory
Date:	2019-07-19
Issue Date:	2019-09-03 14:28:34 (UTC+8)
Publisher:	國立中央大學
Abstract:	數十年來，中壢特高頻雷達利用空間域雷達干涉法，對散塊E層場沿電漿不規則體（Field-aligned Irregularities (FAIs)）進行空間定位與頻譜特性分析，已累積大量的研究成果。研究過程中，若欲對FAIs進行精確的空間定位，則雷達系統的初始相位偏差估計與校正就非常重要。過去，中壢特高頻雷達利用FAIs的場沿特性，配合國際地磁參考場（International Geomagnetic Reference Field (IGRF)）模型，計算FAIs的理論來向角分布，再與觀測到的FAIs來向角分布做比較，用以估算各接收頻道間的系統初始相位偏差。本研究針對此種演算法進行改良，並利用蒙地卡羅方法（Monte Carlo method）模擬FAIs在來向角平面上的分布，結果顯示，此模擬分布與真實分布型態相當一致，足以用來表達真實的FAIs回波分布。此外，本研究重新推導FAIs回波點與中壢特高頻雷達站址，在World Geodetic System 1984 (WGS84)橢球坐標上的幾何關係，以期計算出更精確的FAIs預測回波區域。另一方面，本研究引進新型態的觀測目標物，包括搭載Automatic Dependent Surveillance – Broadcast (ADS-B)系統的民航機與搭載Real Time Kinematic (RTK)系統的多軸飛行器，用以做為參考目標物來進行系統初始相位偏差的估計。結果顯示，利用民航機與多軸飛行器所估計出的系統初始相位偏差相當一致，經由此交互驗證，顯見若以民航機與多軸飛行器做為參考目標物，皆能提供基本且可靠的系統初始相位偏差估計結果。然而利用FAIs的場沿特性所估計出的系統初始相位偏差卻與前兩者不同，本研究就此估計結果間的差異進行了詳細討論。利用所估計出的系統初始相位偏差，本研究對2017年與2018年夏季，共四個月的FAIs觀測資料進行精確空間定位與頻譜特性分析，除了發現FAIs平均都卜勒速度有明顯的日變化，還發現層狀FAIs的高度日變化有雙層結構。此外，利用精確的空間域雷達干涉法，本研究得以對FAIs結構的垂直都卜勒速度切變進行估算與統計，發現都卜勒速度切變與FAIs發生率、平均頻譜寬、平均回波強度三者之間，各有統計上的相關性。;The phase imbalance between receiving channels of a phase array antenna, referred to as phase offset, is one of the most crucial parameters in positioning the targets in lower and upper atmospheres using spatial domain interferometry (SDI) technique. In this study, we develop a method of using commercial aircraft that equips with Automatic Dependent Surveillance-Broadcast (ADS-B) system to estimate the system phase offsets of the Chungli VHF radar. The aviation data broadcasted from ADS-B system combined with the radar returns from the aircraft can obtain the system phase offset. The principle of the method and the algorithms of processing the ADS-B messages are described and the procedures of analyzing the aircraft echoes are also detailed in this study. On the basis of this method, multirotor equipped with a high precision GPS receiver is also employed to estimate radar system phase offset. The results show that the system phase offsets estimated by the aircraft and those from the multirotor are consistent. However, the aircraft/multirotor-derived system phase offsets are very different from those estimated from the radar returns of the 3-meter ionospheric field-aligned plasma irregularities (FAIs) combined with International Geomagnetic Reference Field 12th generation (IGRF-12) model. The principle of the FAIs method is introduced and the plausible causes of the discrepancies in the estimated system phase offsets between aircraft/multirotor and FAIs are discussed. Additionally, based on the estimation result of phase offsets of Chungli VHF radar, the calibrated interferometry results of FAIs during four months in summer are calculated, that is, the fine structure of FAIs can be constructed clearly. The interferometry result shows that the statistical characteristics of total power, spectral width, Doppler shift, height and Doppler velocity shear of FAIs structure have temporal and spatial variations in Es region, furthermore, comparisons between characteristics of FAIs are made and discussed in this study.
Appears in Collections:	[Graduate Institute of Space Science] Department of Earth Sciences

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