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Weather forecasting is the application of science and technology to predict the state of the atmosphere for a given location and over the years many techniques have been used to forecast the weather, Satellite technology is one of it. The history of weather forecasting and early satellite programmes was told using archive film, highlighting the difficulties associated with a lack of weather data. Two hundred dedicated weather satellites have been launched since the 1960s. Together, these satellites enable us to monitor every weather system around the world and to see the weather as it approaches.
Weather prediction can save lives, especially in tropical regions as information from satellites is used to track hurricanes as they develop. The first satellite completely dedicated to weather forecasting was developed by NASA. The satellite was named TIROS-I (television and infrared observation satellite) and was launched on 1st April, 1960.
The weather satellite is a type of satellite that is primarily used to monitor the weather and climate of the Earth.
Satellites can be polar orbiting, covering the entire Earth asynchronously, or geostationary, hovering over the same spot on the equator. Meteorological satellites see more than clouds and cloud systems. City lights, fires, effects of pollution, auroras, sand and dust storms, snow cover, ice mapping, boundaries of ocean currents, energy flows, etc., and other types of environmental information are collected using weather satellites. Weather satellite images helped in monitoring the volcanic ash cloud from Mount St. Helens and activity from other volcanoes such as Mount Etna. Smoke from fires in the western United States such as Colorado and Utah have also been monitored.
Other environmental satellites can detect changes in the Earth’s vegetation, sea state, ocean color, and ice fields. Weather satellites carry instruments called radiometers (not cameras) that scan the Earth to form images.
These instruments usually have some sort of small telescope or antenna, a scanning mechanism, and one or more detectors that detect either visible, infrared, or microwave radiation for the purpose of monitoring weather systems around the world. The measurements these instruments make are in the form of electrical voltages, which are digitized and then transmitted to receiving stations on the ground. The data are then relayed to various weather forecast centers around the world, and are made available over the internet in the form of images. Because weather changes quickly, the time from satellite measurement to image availability can be less than a minute. Most of the satellites and instruments they carry are designed to operate for 3 to 7 years, although many of them last much longer than that. Weather satellites are put into one of two kinds of orbits around the Earth, each of which has advantages and disadvantages for weather monitoring.
The first is a “geostationary” orbit. Geostationary weather satellites orbit the Earth above the equator at altitudes of 35,880 km (22,300 miles). Because of this orbit, they remain stationary with respect to the rotating Earth and thus can record or transmit images of the entire hemisphere below continuously with their visible-light and infrared sensors. This allows the satellite to view the same geographic area continuously. The news media use the geostationary photos in their daily weather presentation as single images or made into movie loops. For instance, GOES-East and GOES-West provide coverage of much of the Western Hemisphere, from the western coast of Africa to the West Pacific, and the Arctic to the Antarctic. The European Space Agency’s Meteosat satellite provides coverage of Europe and Africa. The disadvantages of a geostationary orbit are:
(1) Its very high altitude, which requires elaborate telescopes and precise scanning mechanisms in order to image the Earth at high resolution (currently, 1 km at best); and (2) only portion of the earth can be viewed. The other orbit type is called near-polar, sun-synchronous (or just “polar”), where the satellite is put into a relatively low altitude orbit (around 500 miles) that carries the satellite near the North Pole and the South Pole approximately every 100 minutes. Unlike the geostationary orbit, the polar orbit allows complete Earth coverage as the Earth turns beneath it. Polar orbiting weather satellites offer a much better resolution than their geostationary counterparts due their closeness to the Earth.
The world’s first polar weather satellite system, referred to as TIROS operational system (TOS), became a reality in the year 1966 with the launch of ESSA-1 and ESSA-2 satellites, on 3 February 1966 and 28 February 1966 respectively. These orbits are “sun-synchronous”, allowing the satellite to measure the same location on the Earth twice each day at the same local time. Of course, the disadvantage of this orbit is that the satellite can image a particular location only every 12 hours, rather than continuously as in the case of the geostationary satellite. To offset this disadvantage, two satellites put into orbits at different sun-synchronous times have allowed up to 6 hourly monitoring.
But because of the lower altitude (500 miles rather than 22,000 miles), the instruments the polar-orbiting satellite carries to image the Earth do not have to be as elaborate in order to achieve the same ground resolution. Also, the lower orbit allows microwave radiometers to be used, which must have relatively large antennas in order to achieve ground resolutions fine enough to be useful. The advantage of microwave radiometers is their ability to measure through clouds to sense precipitation, temperature in different layers of the atmosphere, and surface characteristics like ocean surface winds. Because of their global coverage, some of the measurements from polar orbiting satellites are put into computerized weather forecast models, which are the basis for weather forecasting. Today, many countries of the world other than the USA have their own weather satellite systems to monitor the weather conditions around the globe. These include China, Japan, etc.
The NY Times reports that some experts say it is almost certain that the U.S. will soon face a year or more without crucial weather satellites that provide invaluable data for predicting storm tracks. Which apparently was the birthplace of weather satellites. This is happening because the existing polar satellites are nearing or beyond their life expectancies, and the launching of the next replacement. So the replacement of satellites is also an important issue to be considered for any country. Over the years even India has launched many weather satellites one of which was launched recently in October 2012, which was India’s maiden satellite mission to decode monsoon and climate changes, in which its polar rocket successfully put an Indo-French satellite into orbit that also proved its reliability for the 19th time in a row.
So due to inherent advantages of monitoring from space, coupled with advances in sensor technology, satellites have brought about a revolution in weather forecasting. The end result is that there is a reliable forecast of weather and other related activities on a routine basis. With the help of these satellites even pollution whether it’s nature-made or man-made can be pinpointed. The visual and infrared photos show effects of pollution from their respective areas over the entire earth. Aircraft and rocket pollution, as well as condensation trails, can also be spotted. The ocean current and low level wind information gleaned from the space photos can help predict oceanic oil spill coverage and movement and all the information can be easily found out.
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