| 摘要: | 本篇論文利用中央大學的雷達站，架設台陽公司的Ka 波段地面天線系統，觀測時間由2003年至2004年系統所接收的資料，針對功率計接收19.5GHz的單頻訊號、大氣自動氣象站所接收的天氣資料進行長期的統計分析，這些天氣資料包含風向、風速、溫度及溼度，目的主要是研究Ka 波段對流層訊號閃爍。而這些統計分析包括利用微分法及移動平均法分別對功率進行計算，功率標準差與風速、溫度、溼度標準差做相關性分析，功率頻譜斜率與風向、風速、溫度及溼度之間的影響，以及探討功率頻譜斜率日變化情形。 由於Ka 波段地面天線系統為短距離的地面傳播，在功率頻譜分析中，實際觀測結果上因大氣折射指數不規則擾動及降雨影響，造成頻譜上只存在電磁波散射特性。 在分析訊號擾動與各大氣參數上的關係發現，功率標準差皆與各大氣參數標準差散佈圖之相關係數成正相關，主因為風速會造成天線基座跟天線盤面共振，而造成大氣折射指數擾動使得訊號擾動因子為溫度與比濕，而比濕擾動使得訊號擾動的貢獻量大於溫度擾動。平均溫度和平均比濕的上升，頻譜斜率會因此會絕對值變大；平均風速在大於4~5(m/s)，斜率平均值絕對值變小。平均溫度之標準差和平均比濕之標準差上升，頻譜斜率會因此會絕對值變大，風速標準差對平均頻譜斜率並無顯注關係。風向與頻譜斜率無關聯，但在春秋季時在風向60度頻譜斜率較其他方向平緩；而經由以上統計分析可建立在短距離地面傳播訊號閃爍特性。 In order to study tropospheric scintillation at 19.5GHz, from 2003 to 2004 year, we setup a Ka-band terrestrial communication system to receive the single strength affected by tropospheric refractivity irregularities. The weather information, such as wind speed, wind direction, temperature, and specific humidity, were also collected simultaneously. The differential and running mean methods were employed to analyze the signals and the correlation between signal strength, wind speed, temperature, and specific humidity were calculated. We also discuss the characteristics of the slope of the power spectrum of the signals to try to realize the relation between the spectral slope and weather parameter. The results show that positive correlations between signal intensity, wind speed, temperature, and specific humidity, were seen, in which we believe that the wind speed is major factor causing the scintillation of the signals. We also found that when the mean value of temperature and specific humidity were layer, the power spectral slope become steeper. However, where the wind speed is greater than 4m/s, the power spectral slope become gentle, and variance of wind speed seems not to show the correlation with power spectral slope. The diurnal variation of the spectral slope was also presented and discussed in this thesis. |
