What is measured:
Ozone density profiles, temperatures and OH concentration simultaneously at night.
OH measurements at daytime require a change in the setup.

The DIAL (differential absorbtion lidar) technique enables the average concentration of the absorbing gas of interest, in this case ozone, to be measured over a selected range interval by measuring the difference in the lidar backscattered signals for two laser wavelengths tuned on and off an absorption peak of the gas. The Ozone DIAL System uses XeCl excimer laser light (308 nm), the on wavelength. Part of this output is then converted by a hydrogen Raman cell to 353 nm, the off wavelength. The 308 nm wavelength was chosen because it is just off the peak absorption wavelength for ozone; the absorption is weak enough for a double pass through the stratospheric ozone region, but strong enough for range-resolved differential absorption measurements when also using the 353 nm output.

The pulses of 308 nm and 353 nm radiation propagate through the atmosphere simultaneously. As they propagate, radiation at both wavelengths is scattered and absorbed. Radiation at 308 nm is more strongly absorbed by ozone; the strength of its backscattered signal therefore decreases with height more rapidly than that of radiation at 353 nm. The difference in the return signal strengths at the two wavelengths can be related to the ozone concentration by the equations discussed in this section.

The DIAL technique allows the concentration of a gas to be calculated by measuring remotely the backscattered signals at two adjacent wavelengths. Since the laser radiates energy in short pulses, the gas concentration can be measured as a function of distance, or altitude, from the location of the Ozone DIAL System.

The ozone lidar at the ALOMAR Observatory is run on a routine basis during clear sky situations providing ozone profiles in the height range 8 to 50 km. Optional: OH profiles from 70 to 90 km.

Owned by: Andøya Space Center AS (ASC)