ALPS: A Unified Framework for Modeling Time Series of Land Ice Changes

TL;DR

ALPS is a spline-based framework that robustly models complex, non-uniformly sampled land ice change time series, enabling high-resolution reconstructions and new insights into glacier processes.

Contribution

The paper introduces ALPS, a novel localized penalized spline method that improves robustness and uncertainty estimation in modeling irregularly sampled land ice time series.

Findings

ALPS performs well across various ice data types.

It enables high-resolution elevation change reconstructions.

It provides reliable uncertainty estimates.

Abstract

Modeling time series is a research focus in cryospheric sciences because of the complexity and multiscale nature of events of interest. Highly non-uniform sampling of measurements from different sensors with different levels of accuracy, as is typical for measurements of ice sheet elevations, makes the problem even more challenging. In this paper, we propose a spline-based approximation framework (ALPS - Approximation by Localized Penalized Splines) for modeling time series of land ice changes. The localized support of the B-spline basis functions enable robustness to non-uniform sampling, a considerable improvement over other global and piecewise local models. With features like, discrete-coordinate-difference-based penalization and two-level outlier detection, ALPS further guarantees the stability and quality of approximations. ALPS incorporates rigorous model uncertainty estimates with all approximations. As demonstrated by examples, ALPS performs well for a variety of data sets, including time series of ice sheet thickness, elevation, velocity, and terminus locations. The robust estimation of time series and their derivatives facilitates new applications, such as the reconstruction of high-resolution elevation change records by fusing sparsely sampled time series of ice sheet thickness changes with modeled firn thickness changes, and the analysis of the relationship between different outlet glacier observations to gain new insight into processes and forcing.