Reconstruction of 3-D Wet Refractivity Structure of the Troposphere Using Simulated GPS Measurements

利用GPS觀測重建三維大氣濕折射度結構

黃成勇(Cheng-Yung Huang) ； 劉說安(Yuei-An Liou) ； 江振慶(Chen-Ching Chiang) ； 林祐任(Yu-Jen Lin)

《航測及遙測學刊》 10卷3期 (2005/09) Pp. 275-286

https://doi.org/10.6574/JPRS.2005.10(3).5

摘要

同化GPS觀測的濕折射度於數值氣象模式中，具有改善氣象預報的潛在助益。地面GPS接收器接收來自四面八方的GPS衛星訊號，當接收器數量夠多的時候，這些訊號交錯形成一個網狀的構造，提供求取網格點的變數值資訊，這樣的觀測一般稱為斷層掃描技術。本研究中，我們以多波道微波輻射計的觀測資料，建構一個大氣環境做模擬並做為參考值（真值），應用新發展的GPS斷層掃描求解技術，重建大氣濕折射度分佈。折射度為壓力、溫度及水氣的函數，而濕折射度為溫度及水氣的函數。研究中假設在一個長、寬各16公里的等高區域內，每隔4公里的長、寬距離，架設一個GPS接收器，共架設5*5=25個GPS接收器。此外，在模擬區域內，將所要研究十公里高度的大氣層切割成十等分或每隔一公里一等份，即在275(5*5*11)網格點內形成4*4*10=160個立體空間，最後利用經過每個立體空間的GPS衛星訊號，以斷層掃描技術重建大氣濕折射度三維分佈，再以真值做驗證。求解的三維濕折射度在3-5 km以下，誤差僅5-10%。在引進地面氣象觀測為約制定及假設高空濕折射度為零的情況下，該誤差可以再降低。此外，我們也求解PODP值來協助結果分析。

關鍵字

全球定位系統 ； 斷層掃描 ； 濕折射度

並列摘要

It is potentially helpful to improve the weather forecasting through assimilating the atmospheric wet refractivity measured with Global Positioning System (GPS) into numerical weather prediction models. In this paper, a tomographic method is developed to reconstruct the 3D wet refractivity structures of the troposphere using ground-based GPS measured slant delay based on an observing system simulation experiment (OSSE)-type approach. The slant delay is derived from a reference atmospheric temperature, pressure, and water vapor profiles (or ”ground truth”) measured by a multi-channel microwave radiometer, which subsequently serve as reference for comparison with the reconstructed 3D wet delay distribution. The reconstruction is possible because a ground network of many GPS receivers that record integrated slant water along the ray paths of the electromagnetic waves provide the required information. In the simulation, a network with 5 by 5 GPS receivers is uniformly distributed. Distance between two conses (5 by 5 by 11 unknown points). The GPS signals that pass through the 160 cubes intersect all over during a certain time interval of interest, and permit the reconstruction. The relative errors of the reconstructed wet refractivity can be as low as 5 to 10% below 3-5 km altitude compared with the ground truth. They can be further decreased when surface meteorological measurements and an assumption of null refractivity at a reasonable height are applied as constraints. In addition, positional dilution of precision (PDOP) factors is computed to assist in the analysis of the results.

並列關鍵字

GPS ； Tomography ； Wet Refractivity