大氣中，水氣含量雖只佔地表所有水分的0.001％，卻影響著許多天氣現象，如降雨或颱風等的形成和演變。因此，若能夠短時間內獲得大氣中水氣含量的資訊，對於天氣狀態的分析及氣象預報有極大的幫助。
本文研究工作的重點，是以前人發展之台灣地區可降水估算模式求得可降水量及轉換因子，再利用台灣各地的GPS接收站觀測資料去求解二次殘差，並將二次殘差反演成單一訊號線上的零次殘差，最後將可降水量和零次殘差配何著所對應的衛星仰角乘上映射函數，即求得單一訊號線通過對流層的斜向水氣含量。斜向水氣含量較可降水量提供了更豐富的小尺度空間水氣資訊。
本研究使用了21個國內站及6個IGS固定站的觀測資料組成網形，並針對2004年敏督利颱風及艾利颱風做個案分析，而零次殘差的變化確實反應了天氣現象的改變。吾人並針對接收站數目對於求解出的零次殘差之影響。在12組接收站與24組接收站的觀測結果對照下，發現兩組殘差變異大至上在0~1.5mm之間。最後，用水氣微波輻射計所量測之斜向水氣含量與本研究之GPS斜向水氣含量做驗證，兩者之方均根誤差僅為1.94mm。未來吾人將利用更多的觀測資料，促使觀測對流層斜向水氣含量之技術更完善，並將結果與GPS斷層掃描技術整合，期許能裨益氣象預報之改進。

The technique of observing water vapor in the atmosphere by GPS signals became popular in recent years, and the precision has already reached the micrometer level.
The purpose of this study is to retrieve the content of water vapor associated to a GPS signal, which is important in the GPS tomographic method. In this research, we use the data of twenty four GPS stations in Taiwan to resolve zero difference residuals. The distances between these GPS stations are too short, so these residuals are relative values to those chosen fixed stations. Then we use the atmosphere model developed by our laboratory to solve the precipitable water vapor (PW) from a fixed station and the slant water vapor (SW) with a GPS signal.
In this paper, we specially observe the track and SW of the No.30 and No.11 GPS satellite, because its data are almost complete, to study the correlation between SW and weather change. In the end, the result verifies with the water vapor radiometer (WVR) and they present good match.

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