The high spectral resolution of the measured millimeter wave spectra allows to use the pressure broadening of the thermal emission lines of the molecules in the atmosphere to retrieve vertical volume mixing ratio profiles of the stratospheric trace gases (fig. 1). The weakly pressure broadened lines of the molecules at high altitudes contribute more to the line center of the resulting spectrum as measured on the ground whereas the molecules at low altitudes contribute more to the wings.
For inversion Tikhonov-Phillips-Regularization or Optimal Estimation Method alternatively can be used. Optional features of the inversion algorithm are the fit of standing waves within the inversion process and the simultaneous retrieval of profiles of several relevant atmospheric constituents.
As an example raw spectra at 278 GHz measured in spring 1997 at Ny-Ålesund, Svalbard, are shown in fig. 2. The sinusoidal undulations caused by standing waves can clearly be seen. After inversion with simultaneous matching of nine standing waves these perturbations are significantly reduced (fig. 3).
The resulting O3 and ClO mixing ratio profiles are shown in fig. 4.