Ray tracing and refraction in the modified US1976 atmosphere

Area of Science:

• Astronomy
• Atmospheric Science
• Geophysics

Background:

• Astronomical refraction is crucial for accurate celestial navigation and observation.
• Existing models often rely on fixed atmospheric parameters, limiting their applicability.
• The US1976 standard atmosphere provides a baseline but requires adaptation for varied conditions.

Purpose of the Study:

• To introduce a novel and adaptable ray-tracing procedure for astronomical refraction calculations.
• To develop the modified US1976 (MUSA76) atmosphere, allowing variable sea-level temperature and pressure.
• To provide a comprehensive method for calculating dry-air refractions and water-vapor corrections.

Main Methods:

• A flexible ray-tracing algorithm was developed for astronomical refraction.
• The US1976 standard atmosphere was modified (MUSA76) to incorporate variable surface conditions.
• Analytical expressions and numerical methods were derived for refraction and humidity corrections.

Main Results:

• The MUSA76 atmosphere and ray-tracing procedure were applied across all apparent altitudes.
• Calculated refractions were compared against established almanacs and tables (Star Almanac, Nautical Almanac, Pulkovo).
• The study analyzed the impact of sea-level pressure, temperature, gradient, and humidity on refraction.

Conclusions:

• The new ray-tracing method provides a flexible and accurate way to compute astronomical refraction.
• The MUSA76 atmosphere model enhances the applicability of refraction calculations under diverse environmental conditions.
• The findings offer improved tools for astronomical observations and geodetic applications.