ATMS 451: Instruments and Observations MWF 11:30 AM 12:20 PM 310c ATG TuTh 10:30 AM 12:20 PM 108 (be prepared for changes) Instructors Joel Thornton Assoc. Professor, Atmospheric Sciences 508 ATG Robert Wood Assoc. Professor, Atmospheric Sciences 718 ATG Course Materials and Logistics 1.No required textbook (I can suggest some) 2.Course materials on website// 3.Buy a laboratory notebook from UBS 4.Form groups of 3-4 by Wednesday for lab work 5.Determine if you can host a weather station Purpose of this Course 1.Enable you to appreciate the relevance of good, quantitative observational data 2.Allow you to experience how such information is obtained, analyzed, and expressed in scientific and technical communications 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 Grading 75% of final grade based on laboratory/analysis work 60% based on 2 formal written reports (thermometry and weather station) 30% on analysis worksheets 10% on quality of laboratory notebook 25% on ~ weekly quizzes based on lecture material NOTE: You are expected to have ~7 weeks of data for the weather stations. Every week of data that is missing is a 10% deduction from your weather report grade. Relevance to Past and Future Work 1.Basic Science: a connected body of agreed upon truths based on OBSERVABLE facts, classified into laws (theories) Observation Hypothesis Experimental Test (measure) ?Uncertainty? Gravitational Lensing Einstein Rings D.E.D 1919 measured bend angle by sun: 2 +/- 0.3 Relevance to Past and Future Work 2. Applied Science/Engineering 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/cm 3. The density of pure gold is 15.5 g/cm 3. The price of gold is currently $51,500 per kg. What do you do? 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? Avoid Significant (Figure) 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 = m/s 2, and the uncertainty estimate is m/s 2. How do you report your result? Define what is meant by Measurement Measurement determination of size, amount, or degree of some object or property by comparison to a standard unit Measurements are meant to be compared 1.Comparisons (two measurements or measurement vs predictions) come down to a range over which we are confident about our conclusions 2.Often, measurements are just the starting point, and some property calculated from the measurements is the point of comparison: must understand how confidence in measurements propagate through the calculations 3.It is as important to know how the estimate of confidence in the measurement is made, as it is to be given a numerical value: give clear descriptions of your approach to uncertainty analysis Define what is meant by Uncertainty 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. All measurements carry uncertainty, often called errors NOT a mistake, cannot be avoided! Error = Uncertainty (for us) cannot be known exactly, only estimated, must explain basis of estimation Sources of Measurement Uncertainty Analytical Sampling Common Types and Sources of Measurement Uncertainty AnalyticalSamplingHow to Minimize Random Electronic noise from sensor circuitry Measure wind velocity in turbulent flow 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 Define precision and its relationship to accuracy Accuracy and Precision Distribution of N Measurements and of Means xx x = x / 10 N = 10; blue N = 10 performed many times, distribution of means; black Normal Error Integral t P(t) 68% w/in 1 95.4% w/in 2 Normal vs Students t-distribution Question Two different weathernuts living in adjacent towns (town A and B) measure the air temperature in their respective 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 o C Town B T Measurements: 9.8, 10.2, 12.8, 14.6, 11.7 o C The uncertainty in any one of weathernut As or weathernut Bs individual measurements = 0.5 o C.