小波理論應用於週波脫落的偵測與修補及基線解算

Abstract

為了達到GPS高精度定位與導航的目的，在觀測資料的前期處理過程中有效的偵測與修補週波脫落是達到目的的重要一步。在進行GPS觀測時，僅僅是幾個週期的相位脫落，就會使我們達到公分級定位與導航的目標變得非常困難。 何謂週波脫落？簡單的說就是在相位觀測資料中由於衛星失鎖而突然產生的相位跳動。失鎖情況的產生原因可能是（1）衛星訊號被周遭地物如樹木、建築物．．．阻隔。（2）由於電離層效應、多路徑效應影響導致訊雜比過低。（3）接收儀本身的雜訊干擾。 所有處理週波脫落的方法皆將週波脫落視為訊號中的不連續變異量，而週波脫落偵測能力的好壞在於使用何種工具萃取出訊號中的微小變異量；本論文利用小波理論提出一個偵測週波脫落的新方法，能有效的偵測出訊號中的微小週波脫落量，並且利用小波分解去除訊號中的隨機雜訊及更為微小的週波脫落量。在相同的觀測時段內，使用此小波方法可以得到更高精度的定位及基線解算。

In order to attain high precision positioning and navigation results with GPS, cycle slips must be correctly repaired at the data preprocessing stage. A slip of only a few cycles can bias measurements enough to make centimetre-level positioning or navigation difficult. What is a Cycle Slip? Briefly it is a sudden integer number of cycles jump in the carrier phase observable caused by the loss of lock of the receiver phase lock loops. Currently, the source for cycle slips can be distinguished in (1) Obstructions of the satellite signal due to surrounding interference. (2) Low SNR ( Signal to Noise Ratio ) due to ionospheric delay, multipath effect, bad DOP…,etc. (3)Failure in the receiver software. For the most part, techniques used in the detection and determination of cycle slips have not changed drastically since the first methods were devised in the early 1980s. The focus has always been on taking cycle slip into the discontinuity of phase observation, and to judge which is the better way for cycle slip detection depends on the tool you use. In this thesis, we develop a new way by using Wavelet transformation. On using this method, we can detect tiny slips and repair other tinier cycle slips and noise by using wavelet decomposition and de-noising. In the same observed sessions, we can get more precise positioning and baseline resolution.