Umkehr Observation

Umkehr observation

Umkehr observation is conducted to determine the vertical distribution of ozone based on continuous observation of sunlight scattered from the zenith sky at solar zenith angles ranging from 60 to 90 degrees. The principle leverages changes in the intensity ratio of two different wavelengths at which ozone strongly/weakly absorbs UV radiation.

Umkehr is German for 'reversal,' and refers to the reversal observed in the plotted curve of the intensity ratio at a certain angle.

Umkehr observation provides information on vertical distribution based on determination of ozone concentrations in 10 layers from the ground to the top of the atmosphere.

It must be conducted in clear zenith sky.

Observation results

Umkehr observation is conducted in the morning and afternoon in clear zenith sky. The inversion point in an Umkehr curve based on such observation depends on ozone concentration. It appears at a smaller solar zenith angle if the amount of ozone is high and vice versa. See the figures below for Umkehr observation results.

If clouds temporarily cover the zenith sky during measurement, reliable data are obtained through modification using observation-based cloud monitoring information.

Umkehr observation results

Umkehr observation results (left: summer; right: winter)

Ozone vertical distribution derived in Umkehr observation

Ozone vertical distribution derived from Umkehr observation (left: summer; right: winter)

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