  The primary focus of the Mars Trace Gas Orbiter (TGO) collaboration between
NASA and ESA is the detection of the temporal and spatial variation of the
atmospheric trace gases using a solar occultation Fourier transform
spectrometer. To retrieve any trace gas mixing ratios from these measurements,
the atmospheric pressure and temperature have to be known accurately. Thus, a
prototype retrieval model for the determination of pressure and temperature
from a broadband high resolution infrared Fourier Transform spectrometer
experiment with the Sun as a source on board a spacecraft orbiting the planet
Mars is presented. It is found that the pressure and temperature can be
uniquely solved from remote sensing spectroscopic measurements using a
Regularized Total Least Squares method and selected pairs of micro-windows
without any a-priori information of the state space parameters and other
constraints.
  The selection of the pairs of suitable micro-windows is based on the
information content analysis. A comparative information content calculation
using Bayes theory and a hyperspace formulation are presented to understand the
information available in measurement. A method of minimization of mutual
information is used to search the suitable micro-windows for a simultaneous
pressure and temperature retrieval.
