Journal of the Korean Society of Surveying, Geodesy, Photogrammetry and Cartography (한국측량학회지)

Korean Society of Surveying, Geodesy, Photogrammetry and Cartography (한국측량학회)
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Research for Time Variation of $C_{20}$ Using GRACE and SLR Measurements

GRACE 및 SLR 자료를 이용한 $C_{20}$의 시계열 변화 연구

  • 황학 (성균관대학교 건설환경연구소) ;
  • 윤홍식 (성균관대학교 사회환경시스템공학과) ;
  • 이동하 (성균관대학교 건설환경연구소)
  • Published : 2008.10.31
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Abstract

The research of global-scale mass redistribution and it changed by Earth gravity filed variation observations, including Earth's oblateness $J_2$(also called low degree spherical harmonic coefficient $C_{20}$), is in continuous progress. Recently, the comparative analysis of geodetic observation SLR can be made by the development of GRACE and other time-variable gravity measurements. In this study, $C_{20}$ time series changes in the value of comparative analysis was got by GRACE monthly Gravity filed model (CSR RL04) for the period April 2002 to May 2008. And comparative analysis the harmonic coefficients of $C_{20}$ was obtained from SLR observations. Signal analysis for two time-series data was made by wavelet transform, CWT(continuous wavelet transform), XWT(cross wavelet transform) and WTC(wavelet coherence) methods. The results indicate that GRACE and SLR values for $C_{20}$ had both decreasing trend, as well as SLR data represent the annual frequencies, and GRACE was semiannual variations. In addition, the results of GRACE and SLR had a strong correlation with the XWT and WTC in an annual cycle.

지구 중력장의 경년변화 관측을 통한 전 지구 차원에서의 대규모 질량이동 및 그 변화에 대한 연구는 지속적으로 진행되고 있다. 여기에는 지구의 편평 정도를 나타내는 $J_2$(또는 지구 중력장모델의 $C_{20}$)에 대한 연구도 포함되며, 최근에는 GRACE를 비롯한 위성중력기술의 개발로 기존의 SLR 등 우주관측기술의 관측결과와 비교분석을 수행할 수 있게 되었다. 본 연구에서는 2002년 4월부터 2008년 5월사이의 GRACE 월별 중력장모델(CSR RL04)을 이용하여 저차항 중력장 구면조화 계수 $C_{20}$의 시계열 변화를 구하고 SLR 관측 자료로부터 얻어진 $C_{20}$ 값과 비교분석을 수행하였다.시계열 데이터의 분석에는 웨이블릿 변환 신호분석기법을 사용하였으며,구체적으로 연속 웨이블릿 변환,직교 웨이블릿 변환 및 웨이블릿 상관간계 분석을 수행하였다.분석 결과, GRACE와 SLR의 $C_{20}$ 결과는 모두 감소하는 추세를 나타내었으며, 1년 주기를 나타내는 SLR과는 달리 GRACE는 반년 주기에서 더욱 높은 강도를 보였다.또한,GRACE는SLR와의 직교 웨이블릿 스펙트럼 및 상관관계 분석에서도1년 주기에서 매우 강한 상관관계를 보여주었다.

Keywords

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