A microwave sounding unit sounds (produces a profile of) the temperature and the moisture levels in the atmosphere. The first microwave sounding units were placed on National Oceanic and Atmospheric Administration (NOAA) satellites in 1978. In 1998, the Advanced Microwave Sounding Units replaced the older units. The satellites are polar-orbiting and synchronous with the sun. The satellites will make about sixteen orbits in twenty-four hours. The instruments make a scan every eight seconds, during which time the point on the surface below the satellite will have moved by 45 kilometers. During six of the eight seconds, the AMSU-A instrument is making thirty observations about 3œ apart from 48œ on one side to 48œ on the other. The next scan will be 45 kilometers farther along its orbit. After the thirty observations, the instrument makes an observation of a warm calibration target and an observation of cold space before returning to its original starting position. The AMSU-A instrument is determining temperature of the different layers of the atmosphere.

Another instrument, AMSU-B, is scanning in a similar mode but makes three times as many observations and determines water vapor concentration.

In 2005, the AMSU-B instrument was replaced by a Microwave Humidity Sounder (MHS). In 2009 or 2010, the Advanced Technology Microwave Sounder (ATMS) is slated to replace the AMSU-A. The AMSU-A is detecting thermal emissions from atmospheric oxygen. Those emissions are in the microwave region of 23 to 89 gigahertz (Chahine, 2001). The microwave radiation is low-energy and high-frequency. The AMSU-A instrument has several channels. Different channels record different wavelengths of radiation. Groups of channels emphasize different layers of the atmosphere. Combined together a profile of the temperature of the different layers of the atmosphere is produced. Channels 2 through 4 emphasize the surface, channels 5 through 8 emphasize the mid-troposphere, and channels 9 through 14 emphasize the lower stratosphere.

The data obtained from AMSU-A includes temperature and water vapor profiles of the atmosphere, snow and ice coverage, cloud water content, and rain rate. With data from other instruments, scientists can produce not only the temperature and water vapor profiles but also a measurement of the ozone, properties of clouds, and the amount of infrared radiation emitted by the Earth in areas not covered by clouds. The AMSU data are used in weather prediction. The more quickly the data get to weather prediction centers, the better the accuracy of the predictions.

It would appear that the data on temperature profiles that have been acquired since 1958 by balloons and since 1978 by MSU would allow for a determination of the increase or decrease of the temperature of the atmosphere. It has not proven to be so simple. Because of a change in equipment, the balloon data have a discontinuity that makes it much less valuable in determining temperature change. The data from MSU are not temperatures but thermal radiation from oxygen molecules. Different scientists use different methods to calculate the temperatures from the MSU data and consequently obtain different temperatures (Kegawa, 2002). Two of the groups doing calculations of this type are the Remote Sensing System (RSS) and the University of Alabama in Huntsville (UAH). The lower troposphere temperatures, in which stratospheric cooling has been eliminated, has been measured by RSS with an increase of 0.156œ Celsius per decade and by UAH with an increase of 0.13œ Celsius per decade. Other scientists have used the RSS data and the UAH data and have derived increases from 0.050œ Celsius per decade to 0.20œ Celsius per decade.

Climate models indicate that the troposphere should warm about 20 percent more than the surface over the entire world and 50 percent more in the tropics. The surface temperature has increased by 0.17œ Celsius per decade since 1979. Reconsideration of the data from UAH and RSS has led to corrections that have brought the data into fair agreement and into a not inconsistent agreement with the surface data. Probably the best statement about the data was made in a report by the National Research Council. The report states that whether the two sets of data agree with each other or with surface data, the fact is that there is a warming trend. The amount of warming may be less important than the fact that it exists.

References

1. Chahine, Moustafa T. AIRS/AMSU/HSB--The Atmospheric Infrared Sounder, with Its Companion Advanced Microwave Sounding Unit and Humidity Sounder for Brazil: Providing New Insights into Earth's Weather and Climate. Greenbelt, Md.: National Aeronautics and Space Administration, Goddard Space Flight Center, 2001.

2. Kegawa, Seiichiro, and Tsan Mo. An Algorithm for Correction of Lunar Contamination in AMSU-A Data. Washington, D.C.: U.S. Department of Commerce, National Oceanic and Atmospheric Administration, 2002.

Free term papers are not written to satisfy your specific instructions. You can use our professional writing services to buy a custom written research paper, term paper, or essay on Global Warming at affordable price. CustomTermPapers is the best solution for those who seek help in writing term papers, essays, and research papers related to Global Warming and other relevant topics.