ATMS 451: Instruments and Observations

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ATMS 451 Instruments and Observations

• MWF 1130 AM 1220 PM
• 310c ATG
• TuTh 1030 AM 1220 PM
• 108 or 610 ATG (be prepared for changes)

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Instructors
Becky Alexander Assist. Professor, Atmospheric
Sciences 306 ATG beckya_at_uw.edu Robert
Wood Assoc. Professor, Atmospheric Sciences 718
ATG robwood2_at_uw.edu
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Course Materials and Logistics

1. No required textbook (I can suggest some)
2. Course materials on website http//www.atmos.washi
   ngton.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

• 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

• 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?
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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
Sampling
Analytical
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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
N 10 blue N 10 performed many times,
distribution of means black
?x
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Normal Error Integral
95.4 w/in 2?
68 w/in 1?
P(t)
t
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Normal vs Students 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 As or Nut Bs individual measurements
0.5 oC.