To report issues
Call Centre Hotline
An anemometer measures wind speed by a rotating fan (which consists of 3 or 4 cups). Data is collected when the wind propels the fan and is measured by recording revolutions of the fan versus a period of time. Speed may be recorded in miles/hour, metres/second or nautical miles/hour (knots).
A barometer monitors changes in air pressure. There are two types of barometers - mercury barometer and aneroid barometer. The latter may also be linked to a pen that records a clock-driven drum chart. Such an instrument is called a barograph and it provides a continuous record of air pressure with time.
The mercury barometer consists of a glass tube inserted into a dish of mercury. The surrounding air presses down on the mercury in the dish and forces some of the mercury up into the tube. The height to which the mercury rises in the tube is directly proportional to the atmospheric pressure.
A hygrometer measures humidity or the amount of moisture in the air. This is done by measuring the change in length of an organic fibre (e.g. human hair) brought about by the absorption of moisture. A hair hygrometer may be designed to activate
a pen on a clock -driven drum. Such an instrument, called a hydrograph, gives a continuous record of fluctuations in humidity over a given time period.
The human hair cells will indicate the level of moisture in the air by expanding (when air is moist) and contracting (when air is dry).
A psychrometer measures the humidity of the air. To make measurements the wick is dipped in distilled water. One such psychrometer is a Sling Psychrometer (shown on the right) where measurements are taken by whirling the psychrometer with the handle.
Evaporation of water from the wick on the wet bulb thermometer leads to cooling. Using a relative humidity table, the temperature difference between the two thermometers gives the relative humidity of the air (in percent)
A rain gauge measures rainfall over a period of time. It consists of a funnel at the top that directs rainwater into a long and narrow cylinder which is seated inside a larger outer cylinder. A chart in the tilting-siphon rain recorder records the amount of rainfall over the period.
Tilting-siphon Rain Recorder
Rain Gauge
Rain recorder
A helium filled balloon carrying a radiosonde is released twice daily at the Upper Air Observatory. Data such as wind direction and velocity, temperature and relative humidity of the atmosphere up to 100,000 ft are recorded and transmitted to the ground station for further processing.
The weather balloon is inflated with helium gas.
The balloon is released with a radiosonde attached to its base.
© 2017, Government of Singapore
Last Updated on 23 November 2015
National Environment Agency of Singapore All Rights Reserved
National Environment Agency 40 Scotts Road, #13-00 Environment Building Singapore 228231 Hotline: 1800 CALL NEA (1800-225 5632)