Residual ocean tide signal in GRACE(-FO) range-rate post-fit residuals

Ocean tide model imperfections are one of the major uncertainty factors in gravity field recovery. Unmodeled signal can alias into level-2 gravity field products and be interpreted as real signal, e.g. as ice mass loss. An accurate understanding of the ocean tide model imperfections (on spectral and spatial level) is therefore not only important for current, but also for future gravity field missions. For this contribution, we analyzed 20+ years of GRACE(-FO) K-band range-rate post-fit residuals for residual ocean tide signal. The post-fit residuals are obtained as part of the gravity field estimation of monthly solutions. We low pass filter and differentiate range-rate post-fit residuals to obtain residual range-accelerations. Obtained residual range-accelerations are assigned to 5x5 degree grid cells and Lomb-Scargle periodograms for each cell are computed. An analysis of the periodograms reveals peaks at frequencies of ocean tide constituents. The peaks with the largest spectral amplitude can be found at frequencies of the major constituents (O1, M2, K1). In total around 30 constituents are detectable, among them also compound tides and degree-3 tides