CE 738A: Hydrometry - Introduction PDF

CE 738A : Hydrometry Introduction  What is hydrometry? Science of measuring water Metrology Science of measurement and its application What is measurement? The process of associating numbers with physical quantities and phenomenon...

CE 738A : Hydrometry Introduction  What is hydrometry? Science of measuring water Metrology Science of measurement and its application What is measurement? The process of associating numbers with physical quantities and phenomenon The process of experimentally obtaining one or more values that can reasonably be attributed to a quantity together with any other available relevant information Comparison with standards Importance of measurement “If you can’t measure it, you can’t improve it” - Lord Kelvin Hydrological science is built on observations and measurements – theories have emerged from analysis of data collected (Inductivism) OR theories have been confirmed through data (Falsificationism)  Levels of measurement Scales of measurement (S. S. Stevens, 1946) Classify data based on their characteristics and properties Selecting appropriate statistical methods Four levels of measurements  Nominal Scale Categorical data without any order or ranking. Examples: Land use/land cover classes, Soil types Characteristics: o Data is classified into distinct categories. o No mathematical operations can be performed. o Mode is the only measure of central tendency.  Ordinal Scale Categorical data with a ranking or order Examples: River order, Drought categories, Fog categories Characteristics: o Data can be ranked or ordered. o Differences between categories are not equal. o Median and mode can be calculated.  Interval Scale Numerical data with equal intervals between values but no true zero point Examples: Temperature, Time, Water level Characteristics: o Data can be added, subtracted, and averaged. o Ratios are not meaningful. o Mean, median, and mode can be calculated.  Ratio Scale Numerical data with equal intervals and a true zero point. Examples: Precipitation, Discharge, Stage Characteristics: o All mathematical operations can be performed.. o Ratios are meaningful. o Mean, median, mode and geometric mean can be calculated.