The New Concept of GRACE Gradiometry and the Unravelling of the Mystery of Stripes

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dc.contributor.advisorPagiatakis, Spiros D.
dc.contributor.authorPeidou, Athina
dc.date.accessioned2020-08-11T12:39:10Z
dc.date.available2020-08-11T12:39:10Z
dc.date.copyright2020-03
dc.date.issued2020-08-11
dc.date.updated2020-08-11T12:39:10Z
dc.degree.disciplineEarth & Space Science
dc.degree.levelDoctoral
dc.degree.namePhD - Doctor of Philosophy
dc.description.abstractFor nearly two decades, the Gravity Recovery and Climate Experiment (GRACE) and GRACE-Follow On (GRACE-FO) missions have been widely used to quantify mass transfers within the Earth. We perform analysis on the on-board measurements, and we find an interesting correlation between space weather dynamics and disturbances of the on-board measurements. An innovative idea for bringing the two GRACE spacecraft into a differential mode is introduced to fully capture the impact of charged particles on the instrumentation. The idea of differential mode is advanced to a method named gradiometer mode that leads to the estimation of gravitational gradients using GRACE Level 1B measurements. GRACE gradiometer mode is shown to be able to capture geophysical signals at multiscale resolution between [8, 128] spherical harmonics. Both GRACE and GRACE-FO suffer from a disturbing artifact, commonly known as longitudinal stripes, whose origin is yet to be determined. The presence of stripes in GRACE gravity models conceals geophysical signals and degrades the capability of the mission to quantify smaller scale mass transfers (< 200 km). In an effort to discover the origin of stripes, we scrutinize the missions instrumentation, twin-spacecraft configuration and orbital characteristics, to conclude that the GRACE spatial sampling pattern is responsible for the stripe artifacts. GRACE sampling characteristics are quantified and used to prove that the stripes are sub-Nyquist (pseudo-moir) artifacts. We show that the stripes are the result of oversampling the low frequency geoid along the east-west (latitudinal) direction. The low-frequency geoid modulates the total sampled gravitational signal with a frequency near (m/n)fs, where fs is the sampling frequency of the GRACE ground track bundles along the parallels, and m and n are mutually prime integers, with 2mn. GRACE effective latitudinal sampling frequency is shown to be s=1.14 degrees. We generate synthetic stripes using moir theory and by means of rigorous spectral analysis, it is shown that their spectral and spatial characteristics are very similar to the observed ones.
dc.identifier.urihttp://hdl.handle.net/10315/37695
dc.languageen
dc.rightsAuthor owns copyright, except where explicitly noted. Please contact the author directly with licensing requests.
dc.subjectApplied mathematics
dc.subject.keywordsGRACE space gravity mission
dc.subject.keywordsGravity field
dc.subject.keywordsLEO satellites
dc.subject.keywordsSpace weather
dc.subject.keywordsSatellite gradiometry
dc.subject.keywordsDifferential accelerations
dc.subject.keywordsGeophysical signals
dc.subject.keywordsGRACE longitudinal stripes
dc.subject.keywordsAliasing
dc.subject.keywordsMoire artifacts
dc.subject.keywordsSub-Nyquist artifacts
dc.subject.keywordsWavelet analysis
dc.subject.keywordsArtifacts
dc.titleThe New Concept of GRACE Gradiometry and the Unravelling of the Mystery of Stripes
dc.typeElectronic Thesis or Dissertation

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