eather. The imaging equipment can also help to estimate the level of rainfall during a storm, as well as providing estimates of snowfall and providing estimates of spring snow melting. The non-geostationary orbiting satellites are used for looking more closely at the earth's surface. Typically these satellites are in a polar orbit (i.e. crossing both poles) at an altitude of around 800-900 km. They contain instruments for monitoring the earth's atmosphere and the surface. They use both visible and infrared data to give radiation measurements, temperature profiles and the like. They also monitor incoming particles such as electrons, protons, etc., and using ultraviolet sensors they are able to provide indications of the ozone levels in the atmosphere and monitor the size of the ozone hole. Although not associated with weather some of these satellites perform another valuable task as they receive, process and then retransmit data from search and rescue beacons, SO that people needing rescue can be located anywhere on the earth's surface. There have been several stories of miraculous rescues resulting from the use of these beacons. Private mobile radio Businesses of all types make widespread use of the radio spectrum, and have a great need for communications. Private mobile radio (PMR) has been in existence for many years, and differs from the more familiar mobile phone system in that access is restricted to those with licences. It is usually used for communication of a mobile station with its base, although in many instances two mobile stations can communicate. There are obvious examples like taxis that need to keep in contact with their bases to be able to pick up new customers. Other major users of this type of radio communications are the emergency services. However, there are many other users who make extensive use of this type of communication, and large sections of the VHF and UHF portions of the radio spectrum are allocated to these services. Originally private mobile radio was used to cover a restricted are