global-otl (gotl)

Global GPS ocean tidal loading (OTL) analysis. gotl processes worldwide IGS/GNSS GPS stations through a GipsyX kinematic-PPP -> trajectory-model -> harmonic-analysis pipeline to estimate per-station ocean tidal loading displacement coefficients, then evaluates ocean tide models (TPXO9, FES2014b, EOT20) against the GPS-observed signal.

What it does

The pipeline runs in five phases:

1. GipsyX kinematic PPP - position time series from RINEX, with OTL applied during PPP.
2. LoadDef OTL prediction - Love Numbers -> Green's Functions -> convolution with a tide model -> per-station Harpos .otl loading coefficients.
3. Hardisp - IERS hardisp time series of the predicted loading displacement.
4. SLTM + VTide - a Standard Linear Trajectory Model (trend + jumps + oscillations, fit by IRWLS) strips non-tidal signal; VTide harmonic analysis estimates 11 tidal constituents (M2 S2 N2 K2 K1 O1 P1 Q1 MF MM SSA) with uncertainties.
5. Multi-model comparison - vector misfit of GPS-derived vs modelled loading per constituent.

Algorithms, sign conventions, and file formats are documented in the module docstrings under src/gotl/.

Install

Requires Python >=3.11 and Poetry.

poetry install                 # core pipeline
poetry install --with loaddef  # + mpi4py for LoadDef convolution (needs MPI dev headers)

This installs the gotl CLI.

External dependencies (not included)

This repository contains the analysis code only. To run the full pipeline you also need:

• GipsyX 2.x (JPL) - kinematic PPP engine + reference data.
• LoadDef (Martens et al.) - load-deformation toolkit (Phase 2).
• IERS hardisp - Fortran source is vendored under hardisp/; build with cd hardisp/src && make, then link hardisp_exe.
• Ocean tide model grids - TPXO9-atlas, FES2014b, EOT20 NetCDF files from the model providers.

Large inputs/outputs (RINEX, tide grids, results, caches) are gitignored and supplied via environment variables (GOTL_*).

Usage

gotl run-all                                   # all stations in data/station_registry.csv
gotl run aboa                                  # single station
gotl status                                    # per-station completion table
gotl compare aboa                              # GPS vs tide-model residuals
gotl gen-otl-params aboa --tide-model FES2014  # LoadDef OTL params
gotl gen-hardisp aboa --years 2000,2001        # hardisp time series

Layout

src/gotl/   gotl package (pipeline, sltm, tides, io, gipsy, loaddef, compare, cloud, web)
scripts/    LoadDef / download / cloud helper scripts
hardisp/    IERS hardisp Fortran source
tests/      pytest suite (synthetic fixtures)
data/       station_registry.csv (all other data is external / gitignored)

Tests

poetry run pytest tests/ -v

License

MIT - see LICENSE.

The vendored hardisp/ Fortran is IERS Conventions software and retains its own headers. gotl builds on GipsyX (JPL), LoadDef (Martens et al.), and VTide/UTide; obtain and use those under their respective licenses.