MLS Wave Filtering in Limb-Tracking Observations

If MLS radiances are saturated during the limb-tracking observations, the weighting function does not move in the vertical plane relatively to the tangent point. Depending on its orientation with respect to wave fronts, MLS variance may have maximum response to wave perturbation in case A and minimum response in case B due to the weighting function averaging. When projected onto the horizontal plane, the weighting function averaging depends also on horizontal wavelength and viewing angle (that is defined as the angle between wave propagation and line-of-sight directions). As a result of 3D wave propagation, the instrument wave filter during limb tracking operation peaks at viewing angles of ~110^o and ~250^o, which deviate slightly from 90^o and 270^o as would expected for the situation only involving the horizontal cross-section.

Vertical cross-section

Case A

Case B

Horizontal cross-section

Instrument wave filter as a function of viewing angle