# Angles-Only Navigation via Optical Satellite Measurement with Prior Altitude Constrained

## TL;DR

This paper introduces a low-cost navigation method using satellite angles and altitude data to enable precise location tracking without GPS.

## Contribution

A novel angles-only navigation method using optical satellite measurements and prior altitude constraints for GNSS-denied environments.

## Key findings

- Geolocation error is mainly influenced by the perpendicular projection of orbital error relative to the line-of-sight.
- Geolocation accuracy within 250 m (RMS) was achieved using Globalstar satellites in ground-based experiments.
- Altitude errors significantly impact accuracy at low elevation angles.

## Abstract

This paper presents an angles-only navigation (AON) method utilizing optical observations of a single satellite with known ephemeris and prior altitude constraints given by an altimeter or known topography, which can enable near-ground platforms to achieve autonomous navigation in GNSS-denied environments. By leveraging a star tracker to measure the line-of-sight (LOS) direction of a satellite against a star background, the observer’s location is resolved via triangulation under geometric constraints. Theoretical error models are derived to analyze the influence of satellite position errors, LOS direction errors, and altitude uncertainties on geolocation accuracy. Numerical simulations validate the error propagation mechanisms, demonstrating that geolocation error is primarily determined by the perpendicular projection of orbital error relative to the LOS, increases linearly with LOS distance, and is sensitive to altitude errors at low elevation angles. Ground-based experiments conducted using Globalstar satellites achieve geolocation accuracy within 250 m (RMS), consistent with theoretical predictions. The proposed method offers a practical, low-cost solution for high-precision passive navigation in maritime and terrestrial applications.