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--- instruments:hatpro:hatpro [2016/05/27 12:35] – [Principle of operation] stefan
+++ instruments:hatpro:hatpro [2016/06/11 18:30] – susanne
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 ===== Introduction =====
-Microwave radiometers are very sensitive receivers usually equipped with multiple receiving channels in order to derive the characteristic emission spectrum of the atmosphere. Microwave radiometers are utilized in a variety of environmental and engineering applications, including weather forecasting, climate monitoring, [[https://en.wikipedia.org/wiki/Radio_astronomy|radio astronomy]], as well as monitoring of land and ocean surface properties.
+Microwave radiometers are very sensitive receivers designed to measure thermal electromagnetic radiation emitted by material media like the atmosphere. They are usually equipped with multiple receiving channels in order to derive the characteristic emission spectrum of the atmosphere or extraterrestrial objects. Microwave radiometers are utilized in a variety of environmental and engineering applications, including weather forecasting, climate monitoring, [[https://en.wikipedia.org/wiki/Radio_astronomy|radio astronomy]] and radio propagation studies.
-The atmosphere in the [[https://en.wikipedia.org/wiki/Microwave|microwave spectral range]] (MW) between 1 and 300 GHz is semi-transparent. This means its components like dry gases, water vapor, or [[https://en.wikipedia.org/wiki/Precipitation#Hydrometeor_definition|hydrometeors]] interact with MW radiation but overall even the cloudy atmosphere is not completely opaque in this frequency range.
+Using the [[https://en.wikipedia.org/wiki/Microwave|microwave spectral range]] (MW) between 1 and 300 GHz provides complementary information to the visible and infrared spectral range. Most importantly, the atmosphere and also vegetation is semi-transparent in the MW [1]. This means its components like dry gases, water vapor, or [[https://en.wikipedia.org/wiki/Precipitation#Hydrometeor_definition|hydrometeors]] interact with MW radiation but overall even the cloudy atmosphere is not completely opaque in this frequency range.
 For weather and climate monitoring, microwave radiometers are operated from space [1] [2] as well as from the ground [3]. As [[https://en.wikipedia.org/wiki/Remote_sensing|remote sensing]] instruments, they are designed to operate continuously and autonomously often in combination with other atmospheric remote sensors like for example [[https://en.wikipedia.org/wiki/Millimeter_cloud_radar|cloud radars]] and [[https://en.wikipedia.org/wiki/Atmospheric_lidar|lidars]]. They allow to derive important meteorological quantities such as vertical temperature and humidity profile, columnar water vapor amount, or columnar liquid water path with a high temporal resolution in the order of seconds to minutes under nearly all weather conditions.
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 ===== History of microwave radiometer measurements =====
+First developments of microwave radiometer were dedicated to the measurement of radiation of extraterrestrial origin in the 1930s and 1940s [1]. The first operational microwave radiometer was designed by [[https://en.wikipedia.org/wiki/Robert_H._Dicke|Robert H. Dicke]] in the Radiation Laboratory of Massachusetts Institute of Technology to better determine the temperature of the microwave background radiation. This first radiometer worked at a wavelength 1.25 cm and was operated at the Massachusetts Institute of Technology. Dicke also first discovered weak atmospheric absorption in the MW using three different radiometers (at wavelengths of 1.0, 1.25 and 1.5 cm).
-The first operational microwave radiometer was designed by [[https://en.wikipedia.org/wiki/Robert_H._Dicke|Robert H. Dicke]] in the Radiation Laboratory of Massachusetts Institute of Technology to better determine the temperature of the microwave background radiation. This first radiometer worked at a wavelength 1.25 cm and was operated at the Massachusetts Institute of Technology. Dicke also first discovered weak atmospheric absorption in the MW using three different radiometers (at wavelengths of 1.0, 1.25 and 1.5 cm).
+Soon after satellites were first used for observing the atmosphere, MW radiometers became part of their instrumentation. In 1962 the [[https://en.wikipedia.org/wiki/Mariner_2|Mariner-2 mission]] was launched by NASA in order to investigate the surface of Venus including a MW radiometer for water vapor and temperature observations. In following years a wide variety of MW radiometers were tested on satellites. The launch of the [[https://en.wikipedia.org/wiki/Scanning_multichannel_microwave_radiometer|Scanning Multichannel Microwave Radiometer]] (SMMR) in 1978 became an important milestone in the history of radiometry. It was the first time a conically scanning radiometer was used in space; it was brought in space on board of the NASA [[https://en.wikipedia.org/wiki/Nimbus_program|Nimbus satellite]] [4]. The launch of this mission gave the opportunity to image the Earth at a constant angle of incidence that is important as surface emissivity is angular dependent. In the beginning of 1980, new multi-frequency, dual-polarization radiometric instruments were developed. Two spacecraft were launched which carried instruments of this type: Nimbus-7 and [[https://en.wikipedia.org/wiki/Seasat|Seasat]]. The Nimbus-7 mission results allowed to globally monitor the state of ocean surface as well as surface covered by snow and glaciers. Today, microwave instruments like the Advanced Microwave Sounding Unit [[https://en.wikipedia.org/wiki/Advanced_Microwave_Sounding_Unit|AMSU]], Special Sensor Microwave Imager / Sounder [[https://en.wikipedia.org/wiki/SSMIS|SSMIS]] are widely used not only onboard different satellites but also as ground-based instruments integrated in worldwide observational networks.
-Soon after satellites were first used for observing the atmosphere, MW radiometers became part of their instrumentation. In 1962 the [[https://en.wikipedia.org/wiki/Mariner_2|Mariner-2 mission]] was launched by NASA in order to investigate the surface of Venus including a MW radiometer for water vapor and temperature observations. In following years a wide variety of MW radiometers were tested on satellites. The launch of the [[https://en.wikipedia.org/wiki/Scanning_multichannel_microwave_radiometer|Scanning Multichannel Microwave Radiometer]] (SMMR) in 1978 became an important milestone in the history of radiometry. It was the first time a conically scanning radiometer was used in space; it was brought in space on board of the NASA [[https://en.wikipedia.org/wiki/Nimbus_program|Nimbus satellite]] [4]. The launch of this mission gave a unique opportunity to image the Earth at a constant angle of incidence. In the beginning of 1980, new multi-frequency, dual-polarization radiometric instruments were developed. Two spacecraft were launched which carried instruments of this type: Nimbus-7 and [[https://en.wikipedia.org/wiki/Seasat|Seasat]]. The Nimbus-7 mission results allowed to globally monitor the state of ocean surface as well as surface covered by snow and glaciers. Today, radiometers are widely used not only onboard different satellites but also as ground-based instruments integrated in worldwide observational networks.
+Here we could keep the graphic from the original article
+https://en.wikipedia.org/wiki/Microwave_radiometer#/media/File:Radiometer_227629main_ostm-AMR-RSA.jpg
 =====  Principle of operation =====
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 ===== References =====
+[1] Microwave Remote Sensing—Active and Passive”. By F. T. Ulaby. R. K. Moore and A. K. Fung. (Reading, Massachusetts: Addison-Wesley, 1981 and 1982.) Volume I: Microwave Remote Sensing Fundamentals and Radiometry.
+[2] Thermal Microwave Radiation: Applications for Remote Sensing, C. Matzler, 2006, The Institution of Engineering and Technology, London, Chapter 1.
+[3] http://cetemps.aquila.infn.it/mwrnet/main_files/whatisMWRnet.html
+[4] Passive Microwave Remote Sensing of the Earth, Physical Foundations, Eugene A. Sharkov, Springer-Praxis Books in Geophysical Sciences, Chapter 14: Passive microwave space missions
-  - http://juno.wisc.edu/spacecraft_instruments_MWR.html (INAKTIVE LINK!)
-  - http://noaasis.noaa.gov/NOAASIS/ml/avhrr.html
-  - http://cetemps.aquila.infn.it/mwrnet/main_files/whatisMWRnet.html
-  - Thermal Microwave Radiation: Applications for Remote Sensing, C. Matzler, 2006, The Institution of Engineering and Technology, London, Chapter 1.
-  - Eugene A. Sharkov, “Passive Microwave Remote Sensing of the Earth”, Physical Foundations, Springer-Praxis Books in Geophysical Sciences, Chapter 14: Passive microwave space missions
   - Cimini et al., 2009
   - Klein and Gasiewski, 2000