1. Two types of observations In situ measurement: refers to measurements obtained through direct contact with the respective object. Remote sensing measurement: acquisition of information of an object or phenomenon, by the use of either recording or real-time sensing devices that are wireless, not in physical or intimate contact with the object. Active remote sensingPassive remote sensing Mid-term review Accuracy is the difference between what we measured and the true (yet unknown) value. Precision (also called reproducibility or repeatability) describes the degree to which measurements show the same or similar results. Probability density Reference value Average Measured value Accuracy Precision

2. Random error is the variation between measurements, also known as noise. UnpredictableZero arithmetic mean Random error is caused by (a)unpredictable fluctuations of a measurement apparatus, (b)the experimenter's interpretation of the instrumental reading; Systematic errors are biases in measurement which lead to the situation where the mean of many separate measurements differs from the actual value of the measured attribute. A common method to remove systematic error is through Calibration of the measurement instrument. Random error can be reduced or removed by taking many measurements Expression of Measures: e (unit) ± Δe, e.g., Unit Error: Percent Error:

3. Averaging Variance Standard deviation Simple statistics covariance Correlation coefficient

4. Sensible heat flux Specific heat at constant pressure Kinematic sensible heat flux, sh Sensible heat flux, SH z T z T daytimenighttime 1 1 2 2

5. Estimating Errors of derived variables/Propagation of Errors Consider a quantitywhere A, B, C are measured quantities, The error associated with each of them is. What is the error of the derived variable X? Max error:

6. Significant figures 1.All non-zero digits are significant. 2. In a number without a decimal point, only zeros BETWEEN non- zero digits are significant (unless a bar indicates the last significant digit--see below). 3. In a number with a decimal point, all zeros to the right of the first non-zero digit are significant. A decimal point may be placed after the number; for example "100." indicates specifically that three significant figures are meant For multiplication and division, the result should have as many significant figures as the measured number with the smallest number of significant figures. For addition and subtraction, the result should have as many decimal places as the measured number with the smallest number of decimal places. Rule of arithmetic computation

7. 1. 37.76 + 3.907 + 226.4 = 268.1 2. 319.15 - 32.614 = 286.54 3. 104.630 + 27.08362 + 0.61 = 132.32 4. 125. - 0.23 + 4.109 = 129. 5. 2.02 x 2.5 = 5.0 6. 600.0 / 5.2302 = 114.7 7. 0.0032 x 273 = 0.87 8. (5.5) 3 = 1.7 x 10 2 9. 0.556 x (4.x10 1 - 32.5) = 4. 10. 45. x 3.00 = 1.4 x 10 2 11. 3.00 x 10 5 - 1.5 x 10 2 = 3.0 x 10 5 12. What is the average of 0.1707, 0.1713, 0.1720, 0.1704, and 0.1715? Answer = 0.1712

8. Temperature scales Thermometer Calibrations Three reference points IceTriple Point Steam Kelvin273.15273.16373.15 Celsius0.000.01100.00 1. Liquid in glass thermometer Volume expansion of glass:1.2-2.7x10 -5 per 1.00 o C, Volume expansion of Hg:18x10 -5 per 1.00 o C 2. Maximum thermometer 3. Minimum thermometer

9. Making temperature measurements in the air 1. Air is a poor conductor, thus, a good flow over the sensor should be maintained. 2. Sensor to be thermally insulated from the mounting. 3. To prevent radiation, sensors can be polished or coated to reflect solar radiation and to reduce the absorption of infrared radiation. A shield can also be used to shelter the sensor, but it needs to be aspirated to ensure proper ventilation. 4. Heating by adiabatic compression may occur when a sensor is exposed to air moving at very high rates, e.g., aircraft measurements. Adiabatic heating needs to be corrected. 5. Wetting of a temperature sensor will lower the measured temperature due to evaporative cooling. Upper air measurements can be affected as a sensor goes though a cloud. A special device is needed to prevent sensor wetting. For surface measurements, the radiation shield should keep the sensor dry. Thermometer Response Time inversely proportional to heat transfer rate. proportional to the heat capacity

10. Moisture Measurement Mixing ratio, r Specific humidity, q Relative humidity, h Dew-point

11. For isobaric process Enthalpy Wet bulb temperature Since Sling psychrometer Theory How to operate sling psychrometer

12. Atmospheric pressure measurement Barometers Mercury barometer Temperature correction Gravity correction Fortin Barometer Aneroid Barometer Barographs A barograph, which records a graph of some atmospheric pressure, uses an aneroid barometer mechanism to move a needle on a smoked foil or to move a pen upon paper, both of which are attached to a drum moved by clockwork. An evacuated medal capsule supported by a spring. The expansion and contraction drives mechanical levers such that the tiny movements of the capsule are amplified and Displayed.

13. Precipitation Precipitation refers to any product of the condensation of atmospheric water vapour that is deposited on the Earth's surface. Precipitation rate (R): rain water falling on ground per unit area per unit time Mass flux

14. Ordinary rain gauge Tipping bucket rain gauge Optical rain gauge (ORG) Disdrometer Precipitation radar Relationship between the intensity echo and precipitation Echo strength is measured in units of DBZ (decibels). Measuring the drop size distribution and velocity of falling droplets.

15. dBZ Rainrate (inches per hour) Description 6516+Extreme thunderstorms, possible hail 608.00 Very heavy thunderstorms, possible hail 554.00Heavy thunderstorms 522.50Thunderstorms 471.25Very heavy rain or sleet 410.50Heavy rain or sleet 360.25Moderate rain or sleet 300.10Light rain or moderate snow 20TraceVery light rain or snow