The magnetic field dependency of brightness temperatures at frequencies near the O2 microwave absorption lines

The dependence of microwave brightness temperatures on the Earth´s magnetic field at frequencies within a few megahertz of the O₂ absorption line centers is examined in detail. The azimuthal angular dependence is shown to factor from the radiative transfer equation while the dependence on the angle between the propagation direction and the Earth´s field direction is described by a linear or quadratic polynomial in the square of the cosine of this angle in some typical cases of potential interest for a mesospheric sounder. Dependences of the brightness temperature matrix on the magnitude of the Earth´s field are derived and shown to be different according to whether linear or circular polarization is used