What is Line of Sight (LoS)?

Line of sight (LoS) refers to the direct, unobstructed path between two points, typically between a satellite and a receiver or reference station location. In GNSS and positioning contexts, line of sight represents the straight-line geometric path that signals travel from satellites to ground-based equipment, or rovers.

In Swift Navigation’s Skylark correction service, line of sight corrections are fundamental to providing accurate positioning data. The system generates corrections that include: satellite orbits, satellite clock offsets, code and phase biases, slant ionospheric delays, and slant total tropospheric delays, all calculated along the line-of-sight vector. These corrections represent adjustments to the geometric range between satellite and receiver locations, accounting for various atmospheric and systematic errors that affect signal propagation.

The concept extends beyond simple geometric calculations. For atmospheric modeling, ionospheric corrections are often computed independently for each satellite in the line-of-sight direction, particularly for low elevation satellites where ionospheric pierce points are far from the core network. This approach allows for more accurate correction of signal delays caused by the ionosphere. Read our blog to learn more about atmospheric modeling in GNSS corrections.

Line of sight is also critical for system availability and reliability. SBAS (Satellite-Based Augmentation System) satellites require continuous line of sight to decode correction data, which can be challenging in automotive applications where the sky may be obstructed by terrain, buildings, or other vehicles. This limitation highlights why internet-delivered corrections like Skylark can provide better availability compared to satellite-delivered systems.