A weather station may sense and report (and record) several aspects of the local environment:

• air temperature
• wind speed and direction
• barometric (atmospheric) pressure
• relative humidity
• cumulative rainfall (precipitation) over some time interval (hour, day, week, month, year).
• solar irradiance (sunlight)
• lightning strokes
• ground movement (seismometer)

Additionally, it may be useful to measure parameters of interest to farmers:

• evapotranspiration (movement of water from soil)
• soil moisture level
• soil temperature

We will look at sensors and measurements for the following:

• air temperature
• wind speed and direction
• rainfall

Given a Sensor, Make an Instrument

All sensors are transducers. A sensor must have a behavior which makes it a useful reporter of fact. A thermometer, for example, does not really “know” what temperature is, but it does contain something which responds consistently and repeatably to the physical phenomenon we call temperature. Whether or not it is a column of fluid in a glass tube, as an instrument, the thermometer depends on some well-known material behavior. As the air around a thermometer warms, the thermometer itself responds predictably.

So, if we understand the relationship between a phenomenon and a responding device then we can build an instrument.

An instrument produces an indication allowing us to infer the value of an underlying parameter.