The effects of the wavelength locking to the measured signal were also discussed in Chapter 5.2 . In addition to the previous errors, the system calibration is affected by all misalignments of the system. This can easily lead into a range dependence of the received signal. This affects the inversion and furthermore, the measured optical depth. A misalignment also affects the total system transmittance and the signal to noise ratio of the measured signal.
System pointing instabilities make the overlap correction of the received signal difficult.
The overlap region is the close distance range where the overlap of the receiver field of view and the transmitted beam is incomplete. The effect of misalignment between transmitter end receiver pointing directions is largest for the overlap region. The effects vary daily depending from the accuracy of the alignment between transmitter and receiver pointing direction. Large receiver field of views are less critical for the alignment errors. The signal measured with the large field of views of the WFOV channel can be used to align the small field of view channels.