Lesson 16A: Remote Sensing — Analysis of Ozone

 

Estimated Time: Two forty-five minute class periods

Indicator(s) Core learning Goal 1:

1.1.2 The student will modify or affirm scientific ideas according to accumulated evidence.

1.2.1 The student will identify meaningful, answerable scientific questions.

1.4.1 The student will organize data appropriately using techniques such as tables, graphs, and webs. (For graphs: axes labeled with appropriate quantities, appropriate units on axes, axes labeled with appropriate intervals, independent and dependent variables on correct axes, appropriate title)

1.4.2 The student will analyze data to make predictions, decisions, or draw conclusions.

1.4.3 The student will use experimental data from various investigators to validate results.

Indicator(s): Core Learning Goal 2:

2.1.2 The student will describe current efforts and technologies used to study the universe.

Student Outcome(s):

The student will be able to determine the nature of ozone depletion by graphing and analyzing TOMS satellite data images.

Brief Description:

In this lesson students will analyze TOMS (Total Ozone Mapping Spectrometer) ozone concentration data and determine if there is a global problem with ozone depletion or if it is just a localized event. Students will generate graphs using imagery created from the satellite Nimbus-7 along three latitudes of the Southern Hemisphere. Then, students will interpret their graphs to determine if there is indeed a problem with ozone depletion.

Background knowledge / teacher notes:

The following information is ozone background information as it is presented in NASA’s education office’s ambassador investigation "Ozone over your Head".

Ozone is measured in a unit named for British physicist G.M.B. Dobson. The Dobson Unit (DU) is a measure of total ozone, which means that the tropospheric and stratospheric ozone layers are combined into one value.

One DU at sea level, at 0º C would form a layer of ozone only 0.001 cm thick. If 100 DU of ozone were brought to the Earth's surface, it would form a layer only 1 mm thick. So while ozone is important, its volume in the atmosphere is naturally low. Dobson scale values typically fall between 100 & 600 DU. But you will see satellite data and images that have a variety of Dobson values.

Ozone Levels
In tropical areas (low latitudes), ozone levels are typically between 250 and 300 DU year round. However, in temperate regions, seasonal variations can produce large swings in ozone levels. For example measurements in St. Petersburg, Russia, may be as high as 475 DU and as low as 300 DU. These variations are natural and occur even in the absence of man-made ozone depleting chemicals. In discussions of global environmental change "Ozone Depletion" refers to reductions in ozone below normal levels after accounting for seasonal cycles and other natural effects.

The term "ozone hole", which is used to describe the condition of stratospheric ozone, promotes a misconception and probably should not be used. There is no hole. Rather, there is an annual thinning or depletion of stratospheric ozone in the region over Antarctica between September and December.

TOMS
The Total Ozone Mapping Spectrometer (TOMS), is an instrument placed in orbit around the Earth to measure ozone.


Description of TOMS
The instrument has a 60 square kilometer field of view on Earth's surface. TOMS collects 35 measurements every eight seconds as it scans right to left producing approximately 200,000 ozone measurements daily. This covers the entire Earth except areas near the poles. TOMS measures atmospheric ozone by comparing incoming solar radiation with light reflected by the Earth. Therefore, it cannot take measurements at night, or during polar winter (when the sun remains below the horizon 24 hours per day).

TOMS measures ozone by observing both incoming solar energy and "backscattered" ultraviolet (UV) radiation in six wavelengths. "Backscattered" radiation is solar radiation that has penetrated to Earth's lower atmosphere (the troposphere). It is scattered by air molecules and clouds back through the stratosphere to the satellite. In route, some of the UV is absorbed by ozone.

Scientists compare the amount of backscattered radiation to incoming solar energy to calculate the Earth's "albedo". Changes in albedo can be used to measure the amount of ozone above the surface. TOMS measures "total column ozone" the total amount of ozone in an imaginary column of atmosphere from Earth's surface to the satellite.

Additional background information about the TOMS program and about Nimbus-7 is available: http://jwocky.gsfc.nasa.gov/

Ozone shows up in lower concentrations in the Antarctica for many complicate reasons. Some of these are related to the atmosphere being thinner at the poles, a lack of mountainous terrain and well-developed wind patterns.

More background information about ozone and ozone depletion are available at:

http://www.epa.gov/sunwise1/ozonelayer.html

http://www.epa.gov/spdpublc/uvindex/ozoneanduv.html

http://eospso.gsfc.nasa.gov/ftp_docs/Ozone.pdf

Even more ozone information for teachers (and power point presentation) can be found :

http://code916.gsfc.nasa.gov/Personnel/people/Newman,_Paul_A

 

Lesson Description:

ENGAGE

Show the students video clips and a picture of the Nimbus-7 satellite.

An artist's drawing of the Nimbus-7 spacecraft. Available:

http://jwocky.gsfc.nasa.gov/

Ask students what they think the satellite is designed to measure.

Nimbus-7 lithographs may be obtained from the GSFC Educator’s Resource Center.

Education Elements:

IMAGERY

SEES figure 1.05 - TOMS Global Ozone Data Averaged for 1979-1992

http://see.gsfc.nasa.gov/edu/SEES/strat/class/Chap_1/1_Js/1-05.jpg

EXPLORE

Students will use Nimbus-7 TOMS data pictures

Nimbus-7 TOMS Instrument and Satellite Information. Available:

http://jwocky.gsfc.nasa.gov/ to develop data tables and graphs of ozone levels across 14 years of data. Students will chose three different latitudes at which to select data to graph. Then they will determine if the data represents a problem with ozone depletion and to develop hypotheses to explain why the differences in data from each location may have occurred.

Education Elements:

BACKGROUND

This site has a NASA tutorial on ozone depletion.

http://www.nas.nasa.gov/About/Education/Ozone/ozone.html

SCIENTIFIC TOOLS

SEES figure 1.08 - HCl Concentrations Averaged Over 55°S to 55°N for 1992-1998

http://see.gsfc.nasa.gov/edu/SEES/strat/class/Chap_1/1_Js/1-08.jpg

EXPLAIN

Class discussion will review student conclusions and clarify misconceptions about the ozone "hole" over Antarctica.

EXTEND

Students will conduct research to suggest ways to reduce problems/pollutants associated with ozone depletion

Have students share findings with the class.

GT/Career connection: Investigate the current missions, roles of scientists and data analysis for examination of the ozone layer. See NOAA resource below.

Education Elements:

BACKGROUND

This site contains educational resources on sources of stratospheric chlorine.

http://www.nas.nasa.gov/About/Education/Ozone/depletion.html

 

SCIENTIFIC TOOLS

SEES figure 5.03 - Ozone photochemical production.

http://see.gsfc.nasa.gov/edu/SEES/strat/class/Chap_5/5_Js/5-03.jpg

EVALUATE

Journal Write: Students will explain how ozone levels vary throughout the atmosphere and describe ways that we can reduce the problems/pollutants associated with ozone depletion.

 

Materials:

Computers with Internet access, graph paper, colored pencils

 

Resources:

Goddard Space Flight Center Visitor Center has posters with the Nimbus —7 TOMS data published on it.

TOMS. Available:

http://jwocky.gsfc.nasa.gov/

Official Website for information, data, and images from the Total Ozone

Mapping Spectrometer (TOMS) instruments.

Nimbus-7 Total Ozone Mapping Spectrometer (TOMS) Images. Available:

http://seawifs.gsfc.nasa.gov/SEAWIFS/IMAGES/OZONE.html

Images of averages of archived data of the total ozone concentration for the month of October derived from the Nimbus-7/TOMS instrument which was launched on October 1978 and which operated continuously for 14.5 years until TOMS failed on May 6, 1993.

 

Graphing TOMS Images. Exploratorium activity available:

http://www.exploratorium.edu/learning_studio/ozone/graphing1.html

Directions for doing the graphing activity using TOMS data.

The SunWise School Program. Ozone Depletion. Available:

http://www.epa.gov/sunwise1/ozonelayer.html

A short primer on ozone for students from the Environmental Protection Agency.

The Ozone Depletion Homepage. Environmental Protection Agency. Available:

http://www.epa.gov/docs/ozone/index.html

Stratospheric ozone depletion (Antarctic, Arctic, and global). NOAA. Available:

http://www.al.noaa.gov/WWWHD/pubdocs/StratO3.html

A technical document suitable for GT students describing missions to collect data and data analysis.