Gaussian smoothing
Isotropic smoothing in the spherical-harmonic domain. It is kept as a baseline for testing signal loss caused by fixed smoothing radii.
Read related noteMethods
Filtering and Validation Methods
A compact record of each filter family and its routing contract. The catalogue is focused on conventional filtering, Hankel filtering, leakage correction, and product validation used in the GRACE Level-2 workflow.
Fan and decorrelation filtering
Fan filtering and PnMm decorrelation reduce high-degree and correlated north-south stripe errors. Each route is stored as an explicit comparison product.
Read related noteDDK filtering
DDK products represent covariance-aware anisotropic regularization. DDK4 is used as a practical comparison route for signal-retention tests.
Read related noteHSAF / Hankel filtering
Hankel Spectrum Analysis Filtering decomposes latitude-band sequences into quasi-periodic modes and removes stripe-like components while retaining basin-scale hydrological signals.
Read related noteLeakage correction
For lakes, closed basins, and coastlines, surrounding-signal removal and scale-factor restoration are used to reduce leakage-in and leakage-out errors.
Read related noteValidation
Maps, basin series, annual amplitude, trend, RMSE, spectral behavior, Mascon comparison, GLDAS consistency, and altimetry checks are treated as separate evidence layers.
Read related noteComparison checklist
| Dimension | Suggested indicators |
|---|---|
| Noise control | residual stripes, ocean-background RMS, spectral energy |
| Signal preservation | amplitude loss, basin time-series consistency, low-degree spectrum |
| Regional reliability | leakage-in/out, scale factor, basin boundary sensitivity, independent validation |
| Reproducibility | parameter tags, configuration snapshot, processing log, product route |
The methods section records the filtering and validation methods used by the GRACE Level-2 pipeline and visualization software.