Geodesy-EOP-Analysis-Python

Python toolkit for downloading, parsing, and analyzing Earth Orientation Parameters (EOP) from the IERS C04 dataset — including polar motion spectral analysis, Chandler Wobble isolation via FFT, and UT1–UTC time scale conversions.

Physical & Mathematical Background

Earth's orientation is not fixed relative to inertial space or even its own crust. The EOPManager and EOPAnalyzer classes abstract the retrieval and spectral analysis of the IERS C04 celestial reference frame datasets.

1. Polar Motion ($x_p, y_p$)

Polar motion describes the movement of Earth's rotational axis relative to the crust. The two dominant periodic signals are the Annual Wobble (seasonal mass redistribution) and the Chandler Wobble (~433-day free nutation).

The analyzer isolates the Chandler Wobble by applying a Fast Fourier Transform (FFT), filtering the frequency band $f \in [0.7, 1.0]$ cycles/year to determine the free nutation amplitude.

2. Time Scales ($UT1 - UTC$)

Because Earth's rotation rate fluctuates, Universal Time ($UT1$) slowly drifts from Coordinated Universal Time ($UTC$). The analyzer interpolates the $UT1-UTC$ offset from IERS datasets — critical for high-precision GNSS processing and orbit determination.

Installation

git clone https://github.com/AmrFawzy-NavEng/Geodesy-EOP-Analysis-Python.git
cd Geodesy-EOP-Analysis-Python
pip install -r requirements.txt

Quick Start

from geodesy_eop import EOPManager, EOPAnalyzer

# Download and load IERS C04 dataset
manager = EOPManager()
data = manager.load()

# Analyze Chandler Wobble
analyzer = EOPAnalyzer(eop_data=data)
spectrum = analyzer.polar_motion_spectrum()
print(f"Chandler period: {spectrum['chandler_period_days']:.1f} days")
print(f"Chandler amplitude: {spectrum['chandler_amp_arcsec']:.4f} arcsec")

# Convert UTC to UT1
mjd_ut1, offset = analyzer.convert_utc_to_ut1(target_mjd=60000.0)

Example Output

Run python examples/ex02_eop_analysis.py to automatically download the IERS dataset, extract the Chandler wobble, and generate publication-quality plots:

Project Structure

Geodesy-EOP-Analysis-Python/
├── geodesy_eop/
│   ├── __init__.py    # Package exports
│   └── eop.py         # EOPManager (download/parse) + EOPAnalyzer (FFT/time scales)
├── examples/
│   └── ex02_eop_analysis.py
├── requirements.txt
└── LICENSE

Data Source

EOP data is automatically downloaded from the IERS Earth Orientation Centre (public, freely available).

License

MIT — see LICENSE for details.