Add/update Zeeman support for current / future sensors

[BenjaminTJohnson]

Zeeman Effect Overview

• Basic Principle: When an atom or molecule is placed in a magnetic field, its energy levels split into multiple components. This splitting occurs because the magnetic field interacts with the magnetic moments associated with the orbital and spin angular momenta of electrons.
• Spectral Line Splitting: The originally single spectral line splits into several components, with the splitting proportional to the strength of the magnetic field. These components are polarized and shifted in frequency.

Microwave Radiometer Observations

• Frequency Range: Microwave radiometers operate in the microwave frequency range (typically 1-100 GHz), where the Zeeman effect can influence the spectral lines of various atmospheric gases, especially oxygen and water vapor.
• Impact on Observations:
  • Oxygen Lines: The Zeeman effect is significant for the oxygen spectral lines, particularly the 60 GHz and 118 GHz bands, which are used for temperature and pressure profiling of the atmosphere. The magnetic field causes these lines to split, which can be detected and analyzed by microwave radiometers.
  • Polarization: The Zeeman effect introduces polarization in the split components. Microwave radiometers can measure this polarization to provide information on the Earth's magnetic field and its variation with altitude.

This issue

Currently the CRTM has Zeeman predictor support for SSMI/S and AMSUA (see e.g., ODZeeman_Predictor.f90).

This issue is for two items: (1) identifying and adding support for Zeeman effects using the current CRTM paradigm, (2) development of a more generic method for (a) identifying channels that are impacted by Zeeman effects, (b) applying appropriate corrections to the simulated radiances, including line shift, intensity shifts, and polarization rotation. Not yet clear to me whether a "generic" solution is possible, given how closely linked Zeeman effects are to the overall transmittance coefficient training process.