Destriping of GRACE solutions by fitting high‒degree polynomials

Öz

The gravity field solutions from GRACE Gravity Recovery and Climate Experiment system, designed for the determination of the temporal variations in the Earth’s gravity field, has been provided by some data centers during the last decade. These solutions, the so‒called Level 2 L2 Data, consist of fully normalized spherical harmonic coefficients and their standard deviations. In order to monitor the mass variations in the Earth system based on GRACE monthly harmonic coefficients, some systematical errors existing in the solutions should be removed. Several filtering methods have been developed to eliminate or reduce the effects of these errors in the GRACE gravity field solutions. Among them, Gaussian filter is one of the most well known filtering methods. However, this filter is not enough to remove all the systematic errors in the solutions, thus there still remains some errors in the surface mass density or equivalent water thickness maps. To reduce these remaining errors caused by the correlations between the coefficients, an extra de‒correlating filter is necessary in addition to the Gaussian filter. In this study, we focus on the de‒correlation method proposed by Chambers 2006 . The monthly L2 data provided by UTCSR for the time period 2003‒2010 are used. The temporal variations are discussed by applying a seventh degree polynomial and Gaussian filters with different smoothing radii.

Anahtar Kelimeler

• GRACE, Correlation, Filtering, L2 Data

GRACE çözümlerinde korelasyon etkilerinin yüksek dereceden polinomlarla giderilmesi

Öz

Yeryuvarının gravite alanındaki zamansal değişimleri belirlemek amacıyla tasarlanan GRACE Gravity Recovery and Climate Experiment uydu sisteminin sonuç ürünleri son on yıldır çeşitli veri merkezleri tarafından kullanıcılara sunulmaktadır. L2 Seviye - 2 verisi olarak adlandırılan bu veri türü, tam normalleştirilmiş küresel harmonik katsayılarından ve standart sapmalarından oluşmaktadır. Aylık GRACE harmonik katsayıları yardımıyla yer sistemi içerisindeki kütle değişimlerinin izlenebilmesi için, çözümler içinde var olan bazı sistematik hataların giderilmesi gerekmektedir. GRACE gravite alanı çözümlerinde yer alan bu hataların giderilmesi ya da etkilerinin azaltılması için çeşitli filtre yöntemleri tasarlanmıştır. Bunlardan en bilineni Gauss filtresidir. Ancak, söz konusu filtre çözümlerdeki sistematik hataların tamamen giderilmesinde yeterli olmayıp, bu filtre sonunda yüzey kütle yoğunluğu veya eşdeğer su kalınlığı haritalarında halen bazı sistematik hataların varlığı görülmektedir. Katsayılar arasındaki korelasyonların neden olduğu bu hataları gidermek için Gauss filtresinin yanında korelasyon etkilerini de giderecek ek bir filtreye ihtiyaç vardır. Bu çalışmada, Chambers 2006 tarafından uygulanan bir yöntem ele alınmaktadır. Uygulamalar için UTCSR University of Texas at Austin Center for Space Research veri merkezinden alınan 2003‒2010 yıl aralığına ait aylık L2 verisi kullanılmaktadır. Söz konusu katsayılara 7. dereceden polinom ve farklı yumuşatma yarıçapına sahip Gauss filtreleri uygulanarak elde edilen değişimler incelenmektedir.

Anahtar Kelimeler

• GRACE, Korelasyon, Filtreleme, L2 Verisi

Kaynakça

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