Add tropospheric modeling for orbit determination

[ChristopherRabotin]

High level description

Refer to this IERS Tech Note on the calculations for the tropospheric effects based on wavelength.

This implementation should allow for great level of configuration as it will be the basis for the mission-ready orbit determination.

Other references:

• https://gssc.esa.int/navipedia/index.php/Tropospheric_Delay
• https://gssc.esa.int/navipedia/index.php/Electromagnetic_Beam_Bending
• https://www.iers.org/SharedDocs/Publikationen/EN/IERS/Publications/tn/TechnNote36/tn36_132.pdf?__blob=publicationFile&v=1

Requirements

• Nyx shall support tropospheric modeling in its orbit determination module. This modeling shall be frequency-dependent and shall account for the extra delay in the measurement of GNSS signals caused by the troposphere.
• The model shall also account for electromagnetic beam bending.
• The implementation of the tropospheric model shall be based on a well-established technique, such as the Saastamoinen or Niell mapping function.
• The inclusion of tropospheric modeling in the orbit determination module shall improve the accuracy of position estimates.

Test plans

The test plan for the inclusion of tropospheric modeling in the orbit determination module should include the following:

• Verify that the implementation of the tropospheric model is based on a well-established technique, such as the Saastamoinen or Niell mapping function.
• Test the tropospheric model with a variety of input parameters, including different temperatures, pressures, and humidities, as well as different transmitter and receiver antenna locations.
• Compare the position estimates obtained with and without the inclusion of tropospheric modeling. The position estimates with the tropospheric model should be more accurate than those without it.
• Test the tropospheric model with a variety of GNSS frequencies to verify that it is frequency-dependent.
• Verify that the tropospheric model correctly accounts for electromagnetic beam bending.
• Test the tropospheric model in edge cases, such as extreme weather conditions or locations near the poles, where the effect of the troposphere is more pronounced.

In addition to these specific test cases, it is important to ensure that the inclusion of the tropospheric model does not negatively affect the performance of the orbit determination module in other aspects, such as computation time or numerical stability. As such, the test plan should also include a thorough regression testing of the orbit determination module to ensure that no existing functionality is broken.

Design

This is the design section. Each subsection has its own subsection in the quality assurance document.

Algorithm demonstration

If this issue requires a change in an algorithm, it should be described here. This algorithm should be described thoroughly enough to be used as documentation. This section may also simply refer to an algorithm in the literature or in another piece of software that has been validated. The quality of that reference will be determined case by case.

API definition

Define how the Nyx APIs will be affect by this: what are new functions available, do any previous function change their definition, why call these functions by that name, etc.

High level architecture

Document, discuss, and optionally upload design diagram into this section.

Detailed design

The detailed design *will be used in the documentation of how Nyx works.

Feel free to fill out additional QA sections here, but these will typically be determined during the development, including the release in which this issue will be tackled.