Serisel Korelasyonun Toplam Zenit Gecikmesi Zaman Serilerinde Parametrik Olmayan Trend Belirleme Üzerindeki Etkisi

GNSS gözlemlerinin analizinden elde edilen toplam zenit gecikmesi (ZTD) hava şartlarının belirlenmesinde önemli bir parametre olması sebebiyle GNSS tekniğinin iklimsel çalışmalarda da önemli bir yeri vardır. ZTD verilerinden oluşturulan zaman serilerinin trend analizi ile, uzun dönemlerde veride meydana gelen değişimler incelenebilmektedir. Bu çalışmada, Türkiye ve Avrupa’dan seçilen 10 adet IGS (Uluslararası GNSS Servisi) istasyonu için 1995-2010 yılları arasındaki ZTD ürünlerinin COST Aksiyonu ES1206, GNSS4SWEC (Advanced Global Navigation Satellite Systems Tropospheric Products for Monitoring Severe Weather Events and Climate) kapsamında yeniden kestirimi ile elde edilmiş (IGS Repro1) verileri kullanılarak oluşurulan zaman serilerindeki trend ve serisel korelasyon etkisi belirlenmeye çalışılmıştır. Trend analizinde parametrik olmayan yöntemlerden Mann-Kendall testi kullanılmıştır. Serisel korelasyonu belirlemek için otokorelasyon katsayısı hesaplanmış olup seriyi korelasyondan arındırmak için Trend-Free Prewhitening yöntemi uygulanmıştır. Korelasyondan arındırılan seriye tekrar trend analizi yapılarak serisel korelasyonun trendin belirlenmesi üzerindeki etkisi ve Trend-Free Prewhitening yönteminin performansı üzerine irdelemeler yapılmaya çalışılmıştır. Çalışmada IGS istasyonlarındaki ZTD verilerinin tümünde anlamlı serisel korelasyonlar elde edilmiştir. Aynı zamanda LAMA, ONSA ve PENC istasyonlarında Trend-Free Prewhitening uygulandıktan sonra trend olduğu sonucuna varılmıştır. Çalışma kapsamında uygulanan yöntemlerle ilgili hesaplamalar MATLAB program kodları kullanılarak yapılmıştır.

Anahtar Kelimeler:

Mann-Kendall Testi, Serisel Korelasyon, Trend, Trend-Free Prewhitening, Toplam Zenit Gecikmesi

The Effect of Serial Correlation on Nonparametric Trend Determination at Zenith Total Delay Time Series

GNSS technique is important in climate studies because of obtaining Zenith Total Delay which is significant parameter to determine weather conditions with analysis of GNSS observations. Interchanges of long term data can be detected via trend analysis produced by ZTD time series data. In this study, trend and serial correlation effect of time series of (IGS Repro1) were investigated using between 1995-2010 reprocessed ZTD data in the framework of COST Action ES1206, GNSS4SWEC (Advanced Global Navigation Satellite Systems Tropospheric Products for Monitoring Severe Weather Events and Climate). Mann-Kendall test was performed for nonparametric method. The autocorrelation coefficient was calculated to set the serial correlation. Trend-Free Prewhitening method has been applied to eliminate the correlation. The effect on the trend determination of serial correlation and the performance of Trend-Free Prewhitening method were tried to made examination by making re-trend analysis in series which eliminated correlation. As a result of the performed methods, serial correlation is substantial whole ZTD data. At the same time, there are trends in LAMA, ONSA and PENC stations after applying Trend-Free Prewhitening. In this work, MATLAB programming language was handled in all of the tests.

Keywords:

Mann-Kendall Test, Serial Correlation, Trend, Trend-Free Prewhitening, Zenith Total Delay,

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