GRACE zaman serilerinin gürültü karakteri analizi

Yıl 2024, Cilt: 9 Sayı: 1, 45 - 53, 15.04.2024

Özge Güneş , Cüneyt Aydın

https://doi.org/10.29128/geomatik.1307208

Öz

GRACE uydu sistemi 2002’den beri toplam su bütçesi değişimlerinin küresel ölçekte izlenmesine olanak sağlamaktadır. Eşdeğer su kütlesi değişimi cinsinden ifade edilen toplam su bütçesi zaman serilerinin analizinde trend ve mevsimsel sinyalleri içeren fonksiyonel model olan harmonik regresyon yaklaşımı kullanılır. Bu modelde gözlemlerin eşit ağırlıklı ve korelasyonsuz olduğu varsayılmaktadır. Yani, stokastik modelin sadece beyaz gürültüden oluştuğu kabul edilir. Ancak, zaman serisi spektral anlamda analiz edildiğinde zamansal korelasyonların var olduğu ve renkli gürültüyü meydana getirdiği görülmektedir. Bu çalışmada, söz konusu bu gürültüye ilişkin spektral güç yoğunluk değerleri 2002-2022 periyodunu kapsayan, aylık örneklemeli Goddard Space Flight Center mascon veri seti kullanılarak analiz edilmiştir. Toplam su bütçesi değişimi zaman serilerinde negatif spektral indekse sahip renkli gürültü yapısı görülmüştür. Küresel ölçekte gerçekleştirilen analizlerde karasal alanları temsil eden mascon (mass concentration) zaman serilerinde kırpışma gürültüsüne benzer özellikte kesirli Brownian güç spektrumunda tanımlı renkli gürültü olduğu ortaya çıkarılmıştır. Aynı zamanda küresel aylık harmonik katsayılardan filtrelenerek üretilen DDK (Decorrelation Filter) veri seti ile de çalışılmış ve benzer sonuçlar elde edilmiştir.

Anahtar Kelimeler

GRACE, Renkli Gürültü, Zamansal Korelasyon, Stokastik Model, Welch Yöntemi

Kaynakça

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