ATMS 451: Instruments and Observations

1. ATMS 451: Instruments and Observations MWF 11:30 AM – 12:20 PM 310c ATG TuTh 10:30 AM – 12:20 PM 108 or 610 ATG** (be prepared for changes)

2. Instructors Becky Alexander Assist. Professor, Atmospheric Sciences 306 ATG beckya@uw.edu Robert Wood Assoc. Professor, Atmospheric Sciences 718 ATG robwood2@uw.edu

3. Course Materials and Logistics • No required textbook (I can suggest some) • Course materials on website http://www.atmos.washington.edu/~robwood/teaching/451/ • Buy a laboratory notebook from UBS • Form groups of 2 by Wednesday • Determine if you can host a weather station

4. Learning goals • Assess and understand the relevance of good, quantitative observational data • 2. Experience how such information is obtained, analyzed, and expressedin scientific and technical communications

5. Topics and Related Activities 1. Analyzing and Quantifying Measurement Quality 2. Practicalities of Making Measurements 3. Concepts and Realities of Common Sensors 4. Scientific Communication: Report Writing

6. Relevance to Past and Future Work • Basic Science: • Science: a connected body of agreed upon truths based on OBSERVABLE facts, classified into laws (theories) Observation ?Uncertainty? Hypothesis Experimental Test (measure) ?Uncertainty?

7. Gravitational Lensing – Einstein Rings D.E.D 1916 – measured bend angle by sun: 2 +/- 0.3”

8. Relevance to Past and Future Work 2. Applied Science/Engineering

9. Price of Gold A treasure hunter is hawking a 1 kg royal crown she has found, claiming it is solid gold. Your assistant measures its density to be 15 +/- 1.5 g/cm3. The density of pure gold is 15.5 g/cm3. The price of gold is currently $51,500 per kg. What do you do?

10. Measurement Uncertainty Issues • For multiple measurements of the same quantity, what exactly is the “best estimate” of the true value? • X x  x implies a range within which we are “confident ” the true value exists • How do we determine the value of x?

11. Significant Figures – Avoid Significant Embarrassment After a series of measurements and calculations you determine the acceleration due to gravity on Earth. The answer on your calculator/computer is: g = 9.82174 m/s2, and the uncertainty estimate is 0.02847 m/s2. How do you report your result?

12. Measurement Comparison Issues • Need to manipulate uncertainties through mathematical operations  ERROR PROPAGATION • Comparisons (two measurements or measurement vs predictions) come down to a range over which we are “confident” about our conclusions • As important to know how the estimate of uncertainty was made as it is to know the uncertainty

13. Measurement, Error, Uncertainty • Measurement: determination of size, amount, or degree of some object or property by comparison to a standard unit • All measurements carry uncertainty, often called “errors” – NOT a mistake, and cannot be avoided! • Error = Uncertainty (here) – cannot be known exactly, only estimated, must explain basis of estimation

14. Uncertainty • An indefiniteness in measurements of a system property, and any quantities derived from them, due to sensor limitations, problems of definition, and natural fluctuations due to the system itself.

15. Sources of Measurement Uncertainty Sampling Analytical

16. Types and Sources of Measurement Uncertainty

17. Accuracy and Precision

18. Distribution of N Measurements and of Means x = x/10 N = 10;blue N = 10 performed many times, distribution of means; black x

19. Normal Error Integral 95.4% w/in 2 68% w/in 1 P(t) t

20. Normal vs Student’s t-distribution

21. Question Two different weathernuts living in adjacent towns (town A and B) measure the air temperature in their town during a brief period. Both want to claim their town was colder than the other during this time. Does either one have a valid claim? Town A T Measurements: 10.2 11.5 13.4 15.1 12.2 oC Town B T Measurements: 9.8 10.2 12.8 14.6 11.7 oC Average uncertainty in any one of Nut A’s or Nut B’s individual measurements = 0.5 oC.