Analysis of mass variations in Greenland by a novel variant of the mascon approach

• Main Author: Ran, J. (author)
• Other Authors: Klees, R. (promotor), Ditmar, P.G. (promotor), Delft University of Technology (degree granting institution)
• Format: Doctoral or Postdoctoral Thesis
• Language: English
• Published: 2017
• Subjects: Greenland Ice Sheet; GRACE; Ice discharge; melt water; Variance co-variance matrix; mascon; Surface mass balance; Greenland; Ice Sheet
• Online Access: http://resolver.tudelft.nl/uuid:cf99aded-77c9-42da-b0d4-009372620a2e; https://doi.org/10.4233/uuid:cf99aded-77c9-42da-b0d4-009372620a2e

The Greenland ice sheet (GrIS) is currently losing mass, as a result of complex mechanisms of ice-climate interaction that need to be understood for reliable projections of future sea level rise. The thesis focuses on the estimation of mass anomalies in Greenland using data from the GRACE satellite gravity mission. Monthly GRACE gravity field solutions are post-processed using a new variant of the "mascon approach''. Greenland is covered with multiple distinctive "mascons'', assuming the mass anomalies within each one are laterally-homogeneous. Gravity disturbances at mean satellite altitude are synthesized from the GRACE spherical harmonic coefficients. They are used as pseudo-observations to estimate the mascon mass anomalies using weighted least-squares techniques. No regularization is applied. The full noise covariance matrix of gravity disturbances is propagated from the full noise covariance matrix of spherical harmonic coefficients using the law of covariance propagation. Those matrices represent a complete stochastic description of random noise in the data, provided that it is Gaussian. The inverse noise covariance matrix is used as a weight matrix in the weighted least-squares estimate of the mascon mass anomalies. The limited spectral content of the gravity disturbances is accounted for by applying a low-pass filter to the design matrix providing a spectrally consistent functional model. Using numerical experiments with simulated signal and data, we demonstrate the importance of the data weighting and of the spectral consistency between the mascon model and the pseudo-observations. The developed methodology is applied to process real GRACE data using CSR RL05 monthly gravity field solutions with full noise covariance matrices. We distinguish five GrIS drainage systems. The obtained mass anomaly estimates per mascon are integrated over individual drainage systems, as well as over entire Greenland. We find that using a weighted least-squares estimator reduces random noise in the estimates by factors ...