atms 451: instruments and observations mwf 11:30 am – 12:20 pm 310c atg tuth 10:30 am – 12:20 pm...
TRANSCRIPT
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ATMS 451: Instruments and Observations
MWF 11:30 AM – 12:20 PM310c ATG
TuTh 10:30 AM – 12:20 PM108 or 610 ATG** (be prepared for changes)
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Instructors
Becky AlexanderAssist. Professor, Atmospheric Sciences306 [email protected]
Robert WoodAssoc. Professor, Atmospheric Sciences718 [email protected]
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Course Materials and Logistics
1. No required textbook (I can suggest some)
2. Course materials on website http://www.atmos.washington.edu/~robwood/teaching/451/
3. Buy a laboratory notebook from UBS
4. Form groups of 2 by Wednesday
5. Determine if you can host a weather station
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Learning goals
1. Assess and understand the relevance of good, quantitative observational data
2. Experience how such information is obtained, analyzed, and expressed in scientific and technical communications
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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
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Relevance to Past and Future Work
1. Basic Science: Science: a connected body of agreed upon truths based on OBSERVABLE facts, classified into laws (theories)
Observation
Hypothesis
ExperimentalTest (measure)?Uncertainty?
?Uncertainty?
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Gravitational Lensing – Einstein Rings
D.E.D 1916 – measured bend angle by sun:2 +/- 0.3”
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Relevance to Past and Future Work
2. Applied Science/Engineering
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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?
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Measurement Uncertainty Issues
1. For multiple measurements of the same quantity, what exactly is the “best estimate” of the true value?
2. X x x implies a range within which we are “confident ” the true value exists
3. How do we determine the value of x?
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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?
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Measurement Comparison Issues
1. Need to manipulate uncertainties through mathematical operations ERROR PROPAGATION
2. Comparisons (two measurements or measurement vs predictions) come down to a range over which we are “confident” about our conclusions
3. As important to know how the estimate of uncertainty was made as it is to know the uncertainty
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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
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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.
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Sources of Measurement Uncertainty
Analytical Sampling
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Types and Sources of Measurement Uncertainty
Analytical Sampling To Minimize
Random Electronic noise from
sensor circuitry
Turbulence Repetitive measurements
Systematic
Gradations on
thermometer off by 20%
Measure air T over
blacktop parking lot
Calibrate sensor to known
standard; place sensor in
appropriate location
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Accuracy and Precision
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Distribution of N Measurements and of Means
-10 -8 -6 -4 -2 0 2 4 6 8 10
Pro
ba
bil
ity
xt
x
x = x/10
N = 10; blue
N = 10 performed many times, distribution of means; black
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Normal Error Integral
0 0.5 1 1.5 2 2.5 30
0.2
0.4
0.6
0.8
1
t
P(t)
2
21
2
t z
t
P t e dz
68% w/in 1 95.4% w/in 2
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Normal vs Student’s t-distribution
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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.