Dobson spectrometer/unit

The Dobson Unit Imagine that all the ozone in a vertical column of air reaching from the Earth s surface to the top of the atmosphere were concentrated in a single layer of pure 03 at the surface of the Earth, at 273 K and 1.013 x 105 Pa. The thickness of that layer, measured in hundredths of a millimeter, is the column abundance of 03 expressed in Dobson units (DU). The unit is named after G. M. B. Dobson, who, in 1923, produced the first ozone spectrometer, the standard instrument used to measure ozone from the ground. The Dobson spectrometer measures the intensity of solar UV radiation at four wavelengths, two of which are absorbed by ozone and two of which arc not. 

Dobson, Gordon Miller Bourne (1889-1976) British physicist and meteorologist He built the first ozone spectrophotometer and studied the results over many years (now called Dobson spectrometer or Dobsonmeter giving the Dobson unit). 

Figure 11.5 This diagram comes from NASA s ozone monitoring programme TOMS (Total Ozone Mapping Spectrometer). The ozone hole over the Antarctic (shown in purple and pink on the diagram) is largest in the Antarctic spring. Note Dobson Units are a measure of the total amount of ozone in a vertical column from the ground to the top of the atmosphere.

Growth of the Antarctic ozone hole, located mostly over the continent of Antarctica, since 1979. The images were made from data supplied by total ozone-mapping spectrometers (TOMS). The color scale depicts the total ozone values in Dobson units. The lowest ozone densities are represented by dark blue. 

FIGURE 7.3 Antarctic ozone minima. 1979-2003. The ozone minima are given above the data points and the dates of recorded minima are given below the data points. The data, in Dobson units (DU), were measured by the Total Ozone Mapping Spectrometer (TOMS) spacecraft. (Source http // jwocky.gsfc.nasa.gov/multi/ min ozone.gif)... 

This computer image shows the total quantity of ozone over the region near the South Pole, with various colors corresponding to Dobson units (equivalent to the thickness, in units of 10 mm, of total ozone in the atmosphere,assuming it to be compressed to 1 atm at 0°Q.The ozone hole is shown in dark blue,equal to 200 to 225 Dobson units. In September 2002,the ozone hole split into two parts. Data were obtained by theTotal Ozone Mapping Spectrometer (TOMS) aboard the Earth Probe satellite. 

FIGURE 4.45 The Antarctic ozone hole, October 22,1984, as measured by the total ozone mapping spectrometer (TOMS) from the Nimbus 7 satellite. Ozone concentrations are shown in Dobson units. The hole covers the Antarctic continent (SP marks the South Pole) and extends as far north as the tip of South America. Adapted from Stolurski et al. (1986). 

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