It is easy to drop a weather buoy into the ocean and have it measure temperature and pressure as it drifts along, carried by the ocean currents. And you can also place an automatic weather station in Antarctica which will tell you all you wish to know about the local harsh regime.
But until relatively recent times the difficulty has always been that of access to the data; you cannot run a length of wire across the ocean, or telephone a machine for information from the polar ice cap. The answer is a data collection system using satellites.
In this part of the world the most common solution is a French communications system known as Argos. The Argos equipment tends to piggy-back on weather satellites, currently three of the American NOAA polar-orbiting spacecraft.
These circle the world at a height of about 500 miles above the ground, and at intervals no longer than about 90 minutes at least one of them enjoys line-of-sight contact with every possible location on the surface of the Earth.
The Argos equipment aboard the spacecraft receives a burst of data from a transmitter on the buoy or weather station, and uses the Doppler effect on the radio signal to pinpoint the exact location from which the data come.
The times to which the data relate are identified from information included with the signal.
The message is then translated automatically into the internationally agreed code-forms of the World Meteorological Organisation, before being injected by the satellite into the ground-based Global Telecommunications System used for distributing weather information around the world.
More than 1,500 drifting buoys and many hundreds of land stations use the Argos system every day. Many of these measure the wind, the temperature and humidity of the air, and the temperature of the surface of the sea; some also gather data on the salinity of the water and its temperature down to a depth of several hundred metres.
But the Argos system has other more surprising ways of helping meteorologists. One of its other uses, unconnected with the weather, is to monitor the movements of various kinds of wildlife, particularly those species thought to be in any way endangered.
In the southern hemisphere, for example, a selection of albatrosses and emperor penguins is tracked by means of miniature, unobtrusive Argos transmitters fitted on their backs.
In the case of the penguins, when temperature sensors also are attached to them, it has been found that they can send back valuable information about the water temperature at the depths at which they catch their prey.