A long-term installation for measurement of various properties of the atmosphere, wind speed, direction, air temperature and pressure, precipitation, insolation. etc. It is often possible to buy many decades worth of hourly data from these installations, and this can be used in combination with considerably shorter periods of more detailed 10-minute measurements made at the proposed site of a new wind farm to produce good estimates of how much energy a new wind farm could produce in the long term. This is done by the measure, correlate predict process.