Stripe Mystery in GRACE Geopotential Models Revealed

The Gravity Recovery and Climate Experiment (GRACE) gravitational models suffer from a dominant systematic error, usually referred to as "longitudinal stripes." These stripes contaminate useful geophysical signals and limit the spectrum of geoscience applications that can be benefited from GRACE and GRACE-Follow On. Analyses of the spatiotemporal structure of latitudinal stripe profiles show consistent spectral characteristics throughout three years of monthly solutions. Using an elegant combination of GRACE sampling characteristics and advanced moiré theory, we show that the GRACE stripes are sub-Nyquist (pseudo-moiré) artifacts arising from the oversampling of the Earth's low-frequency static disturbing potential (geoid) along the parallels. The low-frequency geoid modulates the total sampled gravitational signal with a frequency near m/n f_s, where f_s is the sampling frequency of the GRACE ground track "bundles" along the parallels of latitude, and m and n are mutually prime integers, with 2m ≤ n.