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"The Missing Link"

ACTIVITY SHEET

Preface: Calibration

Room clock: _______________

Your time: ________________

How many seconds difference is there between the clock and your time?______sec

If your time says it is "9am", what time would the clock in the room read? ______

If the clock in the room says it is "11:34am, 20sec", what time is it to you? ______

-What you have just done, is calibrate your time to the room time.
-Scientists must do this frequently in order to make sure data is correct!!!

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SECTION 1: How do you measure ozone from the ground?

DIRECTIONS: Read each instruction carefully

-Between your head and outer space is a layer of gas called ozone. As you have already learned, ozone protects you from harmful UV sun rays.
-Ozone is measured in Dobson Units.
-1 Dobson Unit = a .01mm layer of ozone at 0C and 1atm pressure.
(Simply put, it is how big the ozone layer would be at the surface and 32°F).
For a more thorough explanation, go to http://jwocky.gsfc.nasa.gov/dobson.html
-Scientists on the Earth can use ground instrument to measure ozone from the surface. Actually, it really measures the amount of UV being absorbed by the atmosphere. Then, it calculates how much ozone must be present to absorb it
(in DU).
-Measurements are usually taken near noon local time.
-There are roughly 350 of these stations located around the world.

LET'S GET ONE PIECE OF DATA...

EXAMPLE:What was the ozone reading for Wallops Island, VA on Jan. 30, 1987?

Step 1- Go to http://www.tor.ec.gc.ca/woudc/stations/stations.htm

...now we have a clickable map.

Step 2- Click on North America
Step 3- Choose the United States of America
Step 4- Scroll down to "Wallops Island"

Now, we know the station number is -------> #107

Step 5- Go to

ftp://woudc:woudc*@ftp.tor.ec.gc.ca/wodc/archive/tot/stn107.tot

Step 6- Scroll down until you see 87/01/30 (this is Jan 30, 1987)

Now, we know that the ozone amount was 331 DU.

1. What is the ozone reading for Wallops Is, Va (st. 107) on Jan 30, 1989?___DU

2. What is the ozone reading for Huancayo, Peru (st. 110) on 2/22/64? _____DU

3a. What station number is BelgranoII, Antarctica (Italy-Argentina)? _________
. b. What was the ozone reading there on 10/1/92? __________DU
. c. What was the ozone reading there on 12/12/92? _________DU
. d. How much did the ozone change over that 70 day time span? _________DU
. e. What do you think caused the reading on 10/1/92?

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SECTION 2: How do satellites measure ozone data?

DIRECTIONS: Read each instruction carefully

- A satellite is just like a ground instrument, however, they are viewing the measurements from above in space.

Step 1- Go to http://jwocky.gsfc.nasa.gov/sat.html
Step 2- Read about the satellites (and look at their pictures) to
answer the questions

4. When did these satellites supply data? Fill in the remainder of the chart below.

- NIMBUS-7, METEOR-3, and ADEOS TOMS have given us ozone information above different cities as well.

EXAMPLE: What was the ozone reading above Arosa, Switzerland on 1/1/80?

SINCE IT WAS 1980, WE NEED TO USE NIMBUS 7 (other's weren't launched yet!)

Step 1- Go to TOMS homepage (http://jwocky.gsfc.nasa.gov)
Step 2- Click on "Ozone Archive" at the top.
Step 3- Click on "NIMBUS-7"
Step 4- Click on "Overpass Data for 371 ground sites
Step 5- Click on "Arosa, Switzerland"
**If you wanted another city, you would simply select it**

Now, we know the answer is 343 DU

5. What is the ozone amount over Arosa, Switzerland on Jan 10, 1979? _____DU
6. What is the ozone amount over Athens, Greece on Feb 1, 1979? ______DU
7. What is the highest ozone amount recorded in Athens, Greece in 1980? ___DU

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SECTION 3: How do we know the satellite is correct?

DIRECTIONS: Read each instruction carefully.

-In the sections above, we have accessed satellite data, and ground data.
-All ground stations are calibrated to Station 83 (Boulder, Colorado). Every Summer from May-August, this station is taken to a high-altitude observatory in Mauna Loa, Hawaii to be recalibrated (picture)

Courtesy: http://mloserv.mlo.hawaii.gov

-TOMS instruments on satellites are calibrated by comparing them to the ground instruments. Let's look at a general example.

Step 1- Go to http://jwocky.gsfc.nasa.gov/multi/arosa2.gif
Step 2- Look at the graph to answer the question below.

8. The blue line is the data taken from Arosa. The green line is TOMS data.
. a. How does TOMS compare to Arosa? ( higher lower exact )
. b. What are the similarities the two instruments have?

9. Think of one reason why they may not EXACTLY match.

-Usually, as long as one instrument is consistently higher, lower, or close to the other, we consider the instruments calibrated.
-In general, in order to calibrate it properly, we need to AVERAGE the data over a period of time. This helps scientists come up with how the ozone (or other data) is changing over long periods of time.
-It is also important to look at the TRENDS and make sure that they match. When ground stations measure a decline in ozone, the satellite should measure a decline as well.

10. Let's look in a little more detail. Using the ground data, and the NIMBUS satellite for Cairo, Egypt, complete the chart below and answer the questions:

11. What are two correlations you noticed between NIMBUS 7 and the ground?
(1)

(2)

12a. What was the average ozone value from NIMBUS-7 over 10 days?______DU
. b. What was the average ozone value from the ground over 10 days? ______DU
. c. What was the difference between the averages? ________DU
. d. What is the percent difference? Round to the nearest whole number.
. . Percent difference = (Av. Ground-Av. NIMBUS) / Av. Ground

_____%

- Basically, we have a general idea how the satellite is calibrated to the ground station, and visa versa. If the percent error were to change dramatically in the next few years, you would know something was wrong.

13. Do this again, this time, let's look at data from Cairo, Egypt in 1993 to see if any major changes have occurred.

14a. What was the average ozone value from NIMBUS-7 over 10 days?______DU
b. What was the average ozone value from the ground over 10 days? ______DU
c. What was the difference between the averages? ________DU
d. What is the percent difference? Round to the nearest whole number.
. . Percent difference = (Av. Ground-Av. NIMBUS) / Av. Ground

_____%

15. Was there any change in percent difference over the last 2 years? _______

16. What two dates in the table above would you suspect faulty data from either the ground or satellite and why?

17. How could you be sure that the satellite was not faulty?

SECTION 4- The case of the missing data.

DIRECTIONS: Read each instruction carefully

-Missing data points occur frequently in science.
-When you are faced with a missing point, you pretty much have to estimate what the missing point would be by looking at the points before and after.
-Scientists use as much information as possible before forming and estimate. This information is used to validate the estimate.

18. There is a missing data point in the NIMBUS-7 overpass data for Cairo, Egypt on Aug. 12, 1982 (day #224).
. a. Go to the TOMS website (http://jwocky.gsfc.nasa.gov/main.html) and estimate what the missing point would be. ______________DU
. b. Go to ground data (ftp://woudc:woudc*@ftp.tor.ec.gc.ca/wodc/archive/tot/st152.tot) to find out what the actual ground measurement WAS. __________DU
. c. What is the difference between the your estimate and the ground measurement? __
. d. What is the percentage difference? ______%
. e. Does the your estimate and the ground data have the same trend? (In other words, do they both decrease or increase from the day before?) ____
. f. Explain if your guess is a good estimate.

19. A harder question. NIMBUS-7 stopped collecting data on May 6, 1993 (day 127). Look at Cairo, Egypt and answer these questions:
. a. Explain if the last data point taken by NIMBUS-7 over Cairo (286DU) is a reliable measurement.

b. . Can you estimate what NIMBUS-7 might have recorded on day 127 (May 6, 1993) had it still been operational? ____________DU

20. The hardest question. METEOR-3 did not take data for an extended period in Dec-Jan 1992. What might METEOR-3 have measured over Melbourne, Australia on Jan. 1, 1992? Be sure to VALIDATE your guess before you are finished!
HINT: This might require the tables on the next page.

_____%

_____%

21. Give two reasons why data verification is important.