Noise Characteristics in GRACE-Mascon Solutions

Güneş Ö. , Aydın C.

International Symposium on Applied Geoinformatics (ISAG2019), İstanbul, Turkey, 7 - 09 November 2019, pp.109

  • Publication Type: Conference Paper / Summary Text
  • City: İstanbul
  • Country: Turkey
  • Page Numbers: pp.109


GRACE (Gravity Recovery and Climate Experiment) satellite system, operated by NASA and DLR, has provided high-resolution information (up to 150 km) about the static and dynamic structure of the Earth's gravity field between 2002 and 2016. The GRACE mission, especially known for its sensitivity to the hydrological events and their temporal changes, has been used in a variety of geodetic and geodynamic studies, such as monitoring variations in the total water storage on the land, the ocean bottom pressure etc. One of the most important products of the GRACE is the socalled Equivalent Water Thickness (EWT). This data is used to determine the total mass storage. The EWT data can be derived from monthly spherical harmonic coefficients (L2 data) or as the final solutions (L3 data: filtered solutions) on the 1ox1o or 3ox3o sized physical surface parts provided by the process centres such as CSR (Centre for Space Research), JPL (Jet Propulsion Laboratory), NASA-GSFC (Goddard Space Flight Centre). The most recent L3 data is the Mascon (Mass concentration) solutions which are provided region by region, basin by basin or Mascon by Mascon. For analysing the EWT time-series, commonly, a harmonic regression model including overall trend, annual and semi-annual periods is used. Generally, it is assumed that only white noise exists in the data. However, the EWT time-series may contain different coloured noises, such as flicker noise, random walk noise, etc., as in every kind of geodetic time-series. Considering these noises in the harmonic regression model is essential because neglecting them in the analysis misleads the statistical decisions about the deduced parameters. In this study, therefore, we investigate the noise characteristic of the basin-bybasin GSFC-Mascon EWT data between 2003 and 2016. For this aim, the log-log Power Spectral Density (PSD) plot of the EWT time-series associated with each basin of the continents except for the Polar Regions is examined. It is known that the slope of the log-log PSD plot gives information about the spectral index of the noise in the time-series: the spectral index is 0, -1 and -2 for white, flicker and random walk noise, respectively. The estimated slope of each log-log PSD plot of the EWT time-series used in this study is significantly different from zero. The average value of the spectral indexes for the basins are about -1.3±0.3. In other words, the EWT data contains coloured noises (dominantly flicker noise) rather than only-white noise. These estimated spectral indexes and their confidence regions are given in the spatial domain to discuss the noise characteristics of the GRACE-Mascon EWT solutions.