6.2 Collection of Weather Data


Can you forecast your health?

You can use a thermometer to better understand your health just like a meteorologist uses one to better understand the weather. A thermometer will help you forecast your health just as it will help to forecast the weather. Other tools, like barometers, also help with weather forecasting.

Collecting Weather Data

To make a weather forecast, the conditions of the atmosphere must be known for that location and for the surrounding area. Temperature, air pressure, and other characteristics of the atmosphere must be measured and the data collected.


Thermometers measure temperature. In an old-style mercury thermometer, mercury is placed in a long, very narrow tube with a bulb. Because mercury is temperature sensitive, it expands when temperatures are high and contracts when they are low. A scale on the outside of the thermometer matches up with the air temperature.

Some modern thermometers use a coiled strip composed of two kinds of metal, each of which conducts heat differently. As the temperature rises and falls, the coil unfolds or curls up tighter. Other modern thermometers measure infrared radiation or electrical resistance. Modern thermometers usually produce digital data that can be fed directly into a computer.


Meteorologists use barometers to measure air pressure. A barometer may contain water, air, or mercury, but like thermometers, barometers are now mostly digital.

A change in barometric pressure indicates that a change in weather is coming. If air pressure rises, a high pressure cell is on the way and clear skies can be expected. If pressure falls, a low pressure cell is coming and will likely bring storm clouds. Barometric pressure data over a larger area can be used to identify pressure systems, fronts, and other weather systems.

Weather Stations

Weather stations contain some type of thermometer and barometer. Other instruments measure different characteristics of the atmosphere, such as windspeed, wind direction, humidity, and amount of precipitation. These instruments are placed in various locations so that they can check the atmospheric characteristics of that location ( Figure below ). Weather stations are located on land, the surface of the sea, and in orbit all around the world.

A land-based weather station

A land-based weather station.

According to the World Meteorological Organization, weather information is collected from 15 satellites, 100 stationary buoys, 600 drifting buoys, 3,000 aircraft, 7,300 ships, and some 10,000 land-based stations.


Radiosondes measure atmospheric characteristics, such as temperature, pressure, and humidity as they move through the air. Radiosondes in flight can be tracked to obtain wind speed and direction. Radiosondes use a radio to communicate the data they collect to a computer. Radiosondes are launched from about 800 sites around the globe twice daily to provide a profile of the atmosphere. Radiosondes can be dropped from a balloon or airplane to makemeasurements as they fall. This is done to monitor storms, for example, since they are dangerous places for airplanes to fly.


Radar stands for Radio Detection and Ranging ( Figure below ). A transmitter sends out radio waves that bounce off the nearest object and then return to a receiver. Weather radar can sense many characteristics ofprecipitation: its location, motion, intensity, and the likelihood of future precipitation. Doppler radar can also track how fast the precipitation falls. Radar can outline the structure of a storm and can be used to estimate its possible effects.

Radar view of a line of thunderstorms

Radar view of a line of thunderstorms.


Weather satellites have been increasingly important sources of weather data since the first one was launched in 1952. Weather satellites are the best way to monitor large-scale systems, such as storms. Satellites are able to record long-term changes, such as the amount of ice cover over the Arctic Ocean in September each year.

Weather satellites may observe all energy from all wavelengths in theelectromagnetic spectrum. Visible light images record storms, clouds, fires, and smog. Infrared images record clouds, water and land temperatures, and features of the ocean, such as ocean currents ( Figure below ).

Infrared view from a satellite of a hurricane

Infrared data superimposed on a satellite image shows rainfall patterns in Hurricane Ernesto in 2006.

An online guide to weather forecasting from the University of Illinois is found here: http://ww2010.atmos.uiuc.edu/%28Gh%29/guides/mtr/fcst/home.rxml.


  • Various instruments measure weather conditions: thermometers measure air temperature, and barometers measure air pressure.
  • Satellites monitor weather and also help with understanding long-term changes in climate.
  • Radar is used to monitor precipitation.

Making Connections

Explore More

Use this resource to answer the questions that follow.


  1. What is contemporary weather forecasting based on?
  2. What do radiosonde balloons do?
  3. What data do satellites collect?
  4. What data is collected by radar?
  5. List other ways weather data is collected.


  1. What can a barometer tell you about the coming weather?
  2. Weather prediction is now much better than it was 30 years ago. Can you figure out why?
  3. Since there are weather satellites, why do you think weather forecasters still use radiosondes?




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