Interpreting the Data
Analysis of the data is a four step process.
  1. Take each reading and correct for the angle of the Sun, i.e. convert the reading to 90o(overhead Sun).
  2. Average each day's corrected readings.
  3. Convert the measured ultraviolet intensity to ozone concentrations.
  4. Plot the ozone concentrations day by day to discover any patterns of change.

Step 1


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 When the solar radiation is observed at a low angle (nearer to the horizon) the length of the optical path through the ozone is increased as shown in the illustration to the left.

The true thickness of the ozone layer is actually less than it would seem based on the amount of uv light measured by the detector.

To get a true estimate of the thickness of the ozone layer we must correct for the angle of the Sun.

To do this we multiply the reading by a correction factor determined by the angle of the Sun.


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The graph to the left gives the value of the correction factor as a function of the solar angle.

Using the graph determine the correction factor for each observation.

Multiply each observation by the appropriate correction factor to obtain the corrected reading.

Record your result for step 2.

Step 2

In general, observations are taken three times each day (weather permitting) using two instruments...giving a total of six readings per day.

When each reading has been corrected for the solar angle (step 1), the readings represent the values of the ultraviolet light intensity from a theoretical Sun directly overhead.

Add up the corrected readings for the day and determine the average ultraviolet measurements for that day.

Repeat the process for each day for which there is data.

Record your result for step 3.

Step 3


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 Use the graph to the left to convert your averaged uv measurements (from step 2) to Dobson Units.

This will give the total amount of stratospheric ozone in the zenith (directly overhead) on the date and at the location for which the observation was made.

Record your result for step 4.

Step 4


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  1. Using your results from step 3, plot the ozone concentrations in Dobson Units for each day of the expedition.

  2. Compare your results with other members of your class.

  3. How do your results compare to measurements made by satellite observations?

Here is a sample you can try, pending the recovery of the expedition's data.

Sample Data for Analysis

Data Analysis Worksheet

Here is the expedition data.

Expedition Data for Analysis

Summary Notes: The Data Set and its Analysis

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