The need for measurements

Whether it be for meteorological, hydrological, oceanographie or climatological studies or for any other activity relating to the natural environment, measurements are vital. Knowledge of what has happened in the past and of the present situation, and an understanding of the processes involved, can only be arrived at if measurements are made. Such knowledge is also a prerequisite of any attempt to predict what might happen in the future and subsequently to check whether the predictions are correct. Without data, none of these activities is possible. Measurements are the cornerstone of them all. This book is an investigation into how the natural world is measured.

The things that need to be measured are best described as variables. Sometimes the word parameter is used but variable describes them more succinctly. The most commonly measured variables of the natural environment include: solar and terrestrial radiation, air and ground temperatures, atmospheric humidity, evaporation and transpiration, wind speed and direction, rainfall and snowfall, barometric pressure, soil moisture and soil tension, groundwater, river level and flow, water quality, sea level, sea surface temperature, ocean currents and waves, properties of the upper atmosphere and the concentration of trace gases, clouds and lightning, visibility and the ice of polar regions.