Meteorological (and related environmental and geophysical) observations are made for a variety of reasons. They are used for the real-time preparation of weather analyses, forecasts and severe weather warnings, for the study of climate, for local weather-dependent operations (for example, local aerodrome flying operations, construction work on land and at sea), for hydrology and agricultural meteorology, and for research in meteorology and climatology. Meteorology is a rapidly moving science. New developments in weather forecasting, climate science and observing techniques are happening all the time. Instrumentation and measurements have been a fundamental part of this course.