An interactive browser-based visualizer for Earth's gravity field using EGM96 spherical harmonic coefficients. Zero dependencies — pure HTML, CSS, and JavaScript.
| Tab | Description |
|---|---|
| Geoid Undulation | World map of N (metres) via Bruns' formula |
| Gravity Anomaly | Free-air gravity anomaly Δg (mGal) |
| Yₙₘ Spectrum | Interactive surface spherical harmonic Yₙₘ(φ,λ) renderer + degree variance spectrum |
| About | Model parameters, references, geodetic constants |
- nmax selector — truncate the series at degree 6, 10, 20, or 36
- Color palettes — Geodetic, Polar, Jet, Viridis
- Hover tooltip — shows lat/lon and field value at cursor
- Yₙₘ panel — enter any n, m (0–20) and cosine/sine type
Geoid undulation (Bruns' formula):
N = T/γ = (GM/γa) · Σ_{n=2}^{nmax} Σ_{m=0}^{n} [C̄ₙₘ cos(mλ) + S̄ₙₘ sin(mλ)] P̄ₙₘ(sinφ)
Free-air gravity anomaly:
Δg = (GM/a²) · Σ_{n=2}^{nmax} (n−1) · Σ_{m=0}^{n} [C̄ₙₘ cos(mλ) + S̄ₙₘ sin(mλ)] P̄ₙₘ(sinφ)
Fully normalized associated Legendre polynomials via Holmes & Featherstone (2002) recurrence.
| Property | Value |
|---|---|
| Model | EGM96 (Lemoine et al. 1998) |
| Exact coefficients | n = 2–7 (NGA published values) |
| Extended (Kaula rule) | n = 8–36 |
| Reference ellipsoid | WGS84 (a = 6,378,137 m) |
| GM | 3.986004418 × 10¹⁴ m³/s² |
| Grid resolution | 2° × 2° (91 × 181 points) |
# Must be served — not file:// (fetch() call for JSON)
python -m http.server 8080
# then open http://localhost:8080- Lemoine et al. (1998). The Development of the Joint NASA GSFC and the NIMA Geopotential Model EGM96. NASA/TP-1998-206861.
- Kaula, W.M. (1966). Theory of Satellite Geodesy. Blaisdell.
- Holmes & Featherstone (2002). A unified approach to the Clenshaw summation. J. Geodesy 76(5):279–299.
Dr. Mosab Hawarey
PhD, Geodetic & Photogrammetric Engineering (ITU) | MSc, Geomatics (Purdue) | MBA (Wales) | BSc, MSc (METU)
- GitHub: https://github.com/mhawarey
- Personal: https://hawarey.org/mosab
- ORCID: https://orcid.org/0000-0001-7846-951X
MIT License