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instruments:hatpro:hatpro [2016/06/11 21:30] susanneinstruments:hatpro:hatpro [2018/07/23 12:51] andreas
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 **HATPRO** (//Humidity and Temperature Profiler//) is a microwave radiometer [[http://en.wikipedia.org/wiki/Remote_sensing|remote sensing]] instrument detecting thermal emission from the [[http://en.wikipedia.org/wiki/Atmosphere| atmosphere]]. We currently operate three HATPRO devices: **HATPRO** (//Humidity and Temperature Profiler//) is a microwave radiometer [[http://en.wikipedia.org/wiki/Remote_sensing|remote sensing]] instrument detecting thermal emission from the [[http://en.wikipedia.org/wiki/Atmosphere| atmosphere]]. We currently operate three HATPRO devices:
 +  * [[instruments:foghat:foghat|FOGHAT]] in [[sites:iquique|Iquique]] in the Atacama desert
   * [[instruments:tophat:tophat|TOPHAT]] at [[sites:joyce|JOYCE]] near (Julich)   * [[instruments:tophat:tophat|TOPHAT]] at [[sites:joyce|JOYCE]] near (Julich)
-  * [[instruments:sunhat:sunhat|SUNHAT]] on [[sites:barbados|Barbados]] 
   * [[instruments:snohat:snohat|SNOHAT]] at the [[sites:ufs|Schneefernerhaus observatory]] (Mt. Zugspitze)   * [[instruments:snohat:snohat|SNOHAT]] at the [[sites:ufs|Schneefernerhaus observatory]] (Mt. Zugspitze)
 +  * [[instruments:sunhat:sunhat|SUNHAT]] on [[sites:barbados|Barbados]]
  
 ===== Introduction ===== ===== Introduction =====
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 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).  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). 
  
-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 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
 + 
 +Ground-Based radiometer for the determination of temperature profiles were first explores in the 1960s [4] and have since themn strongly improved in terms of reduced noises and the ability to run unattended in 24/7 mode within worldwide observational networks [5]. Review articles [[http://www.ursi.org/files/RSBissues/RSB_310_2004_09.pdf|[6] ]], [7] and a detailed online [[http://cfa.aquila.infn.it/wiki.eg-climet.org/index.php5/Microwave_radiometer|handbook]] [8] are available
  
 Here we could keep the graphic from the original article Here we could keep the graphic from the original article
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 Besides the distinct absorption features of molecular transistion lines, there are also non-resonant contributions by hydrometeors (liquid drops and frozen particles). Liquid water emission increases with frequency, hence, measuring at two frequencies, typically one close to the water absorption line (22.235 GHz) and one in the nearby window region (typically 31 GHz) dominated by liquid absorption provides information on both the columnar amount of water vapor and the columnar amount of liquid water separately (two-channel radiometer). The so-called „water vapor continuum“ is arises from the contribution of far away water vapor lines. Besides the distinct absorption features of molecular transistion lines, there are also non-resonant contributions by hydrometeors (liquid drops and frozen particles). Liquid water emission increases with frequency, hence, measuring at two frequencies, typically one close to the water absorption line (22.235 GHz) and one in the nearby window region (typically 31 GHz) dominated by liquid absorption provides information on both the columnar amount of water vapor and the columnar amount of liquid water separately (two-channel radiometer). The so-called „water vapor continuum“ is arises from the contribution of far away water vapor lines.
  
-Larger rain drops as well as larger frozen hydrometeors (snow, graupel, hail) also scatter microwave radiation especially at higher frequencies (>90 GHz). These scattering effects can be used to distinguish between rain and cloud water content exploitinh polarized measurements [5] but also to constrain the columnar amount of snow and ice particles from space [6] and from the ground [7].+Larger rain drops as well as larger frozen hydrometeors (snow, graupel, hail) also scatter microwave radiation especially at higher frequencies (>90 GHz). These scattering effects can be used to distinguish between rain and cloud water content exploitinh polarized measurements [9] but also to constrain the columnar amount of snow and ice particles from space [10] and from the ground [11].
  
 {{:instruments:hatpro:mwr_5.png?600|Microwave spectrum: The black lines show the simulated spectrum (in brightness temperatures TB) for a ground-based receiver; the colored lines are the spectrum obtained from a satellite instrument over the ocean measuring at horizontal (blue) and vertical (red) linear polarization. Solid lines indicate simulations for clear-sky (cloud-free) conditions, dotted lines show a clear-sky case with a single layer liquid cloud. The vertical lines indicate typical frequencies used by satellite sensors like the [[https://en.wikipedia.org/wiki/Advanced_Microwave_Sounding_Unit|AMSU]] radiometer.}} \\ {{:instruments:hatpro:mwr_5.png?600|Microwave spectrum: The black lines show the simulated spectrum (in brightness temperatures TB) for a ground-based receiver; the colored lines are the spectrum obtained from a satellite instrument over the ocean measuring at horizontal (blue) and vertical (red) linear polarization. Solid lines indicate simulations for clear-sky (cloud-free) conditions, dotted lines show a clear-sky case with a single layer liquid cloud. The vertical lines indicate typical frequencies used by satellite sensors like the [[https://en.wikipedia.org/wiki/Advanced_Microwave_Sounding_Unit|AMSU]] radiometer.}} \\
 Fig. 3: Microwave spectrum: The black lines show the simulated spectrum (in brightness temperatures TB) for a ground-based receiver; the colored lines are the spectrum obtained from a satellite instrument over the ocean measuring at horizontal (blue) and vertical (red) linear polarization. Solid lines indicate simulations for clear-sky (cloud-free) conditions, dotted lines show a clear-sky case with a single layer liquid cloud. The vertical lines indicate typical frequencies used by satellite sensors like the [[https://en.wikipedia.org/wiki/Advanced_Microwave_Sounding_Unit|AMSU]] radiometer. Fig. 3: Microwave spectrum: The black lines show the simulated spectrum (in brightness temperatures TB) for a ground-based receiver; the colored lines are the spectrum obtained from a satellite instrument over the ocean measuring at horizontal (blue) and vertical (red) linear polarization. Solid lines indicate simulations for clear-sky (cloud-free) conditions, dotted lines show a clear-sky case with a single layer liquid cloud. The vertical lines indicate typical frequencies used by satellite sensors like the [[https://en.wikipedia.org/wiki/Advanced_Microwave_Sounding_Unit|AMSU]] radiometer.
  
-===== Design and Calibration =====+===== Design =====
 A microwave radiometer consits of an antenna system, microwave radiofrequency components (frontend) and a backend for signal processing at intermediate frequencies (Fig. 5). The atmospheric signal is very weak and the signal needs to be amplified by around 80 dB. Therefore often heteorodyne techniques are used to convert the signal down to lower frequencies that allow the ise of commercial amplifiers and signal processing. Increasingly low noise amplifiers become available at higher frequencies, i.e. up to 100 GHz, making heteorodyne techniques obsolete. Thermal stabilization is highly important to avoid receiver drifts. A microwave radiometer consits of an antenna system, microwave radiofrequency components (frontend) and a backend for signal processing at intermediate frequencies (Fig. 5). The atmospheric signal is very weak and the signal needs to be amplified by around 80 dB. Therefore often heteorodyne techniques are used to convert the signal down to lower frequencies that allow the ise of commercial amplifiers and signal processing. Increasingly low noise amplifiers become available at higher frequencies, i.e. up to 100 GHz, making heteorodyne techniques obsolete. Thermal stabilization is highly important to avoid receiver drifts.
    
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 The calibration of MWRs sets the basis for accurate measured TB and therefore, for accurate retrieved atmospheric parameters as temperature profiles, integrated water vapor and liquid water path. The simplest version of a calibation is a so-called „hot-cold“ calibration using two reference blackbodies at known, but different, „hot“ and „cold“ temperatures, i.e. assuming a linear relation between input power and output voltage of the detector. Knowing the physical temperatures of the references, their TB can be calculated and directly related to detected voltages of the radiometer, hence, the linear relationship between TB and voltages can be obtained. The calibration of MWRs sets the basis for accurate measured TB and therefore, for accurate retrieved atmospheric parameters as temperature profiles, integrated water vapor and liquid water path. The simplest version of a calibation is a so-called „hot-cold“ calibration using two reference blackbodies at known, but different, „hot“ and „cold“ temperatures, i.e. assuming a linear relation between input power and output voltage of the detector. Knowing the physical temperatures of the references, their TB can be calculated and directly related to detected voltages of the radiometer, hence, the linear relationship between TB and voltages can be obtained.
  
-The temperatures of the calibration targets should be chosen such that they span the full measurement range. Ground-based radiometers usually use an ambient temperature target as „hot“ reference. As a cold target one can use either a liquid nitrogen cooled blackbody (77 K) [e.g. Ulaby] or a zenith clear sky TB that was obtained indirectly from radiative transfer theory [Paper Westwater]. Satellites use a heated target as „hot“ reference and the cosmic background radiation as „cold“ reference. To increase the accuracy and stabiltity of MWR calibrations further calibration targets, such as internal noise sources, can be used.+The temperatures of the calibration targets should be chosen such that they span the full measurement range. Ground-based radiometers usually use an ambient temperature target as „hot“ reference. As a cold target one can use either a liquid nitrogen cooled blackbody (77 K) [1] or a zenith clear sky TB that was obtained indirectly from radiative transfer theory [Paper Westwater]. Satellites use a heated target as „hot“ reference and the cosmic background radiation as „cold“ reference. To increase the accuracy and stabiltity of MWR calibrations further calibration targets, such as internal noise sources, or Dicke switches (Fig. 4) can be used.
  
 =====   Retrieval of temperature and water vapor profiles   ===== =====   Retrieval of temperature and water vapor profiles   =====
- 
 The retrieval of physical quantities (e.g. temperature or water vapor profiles) is not straight-forward and comprehensive retrieval algorithms (using inversion techniques like [[https://en.wikipedia.org/wiki/Optimal_estimation|optimal estimation]] approach) have been developed. The retrieval of physical quantities (e.g. temperature or water vapor profiles) is not straight-forward and comprehensive retrieval algorithms (using inversion techniques like [[https://en.wikipedia.org/wiki/Optimal_estimation|optimal estimation]] approach) have been developed.
  
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 [2] Thermal Microwave Radiation: Applications for Remote Sensing, C. Matzler, 2006, The Institution of Engineering and Technology, London, Chapter 1. [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 +[3] Westwater, Edgeworth Rupert, 1970Ground-Based Determination of Temperature Profiles by MicrowavesPH.DThesis, UNIVERSITY OF COLORADO AT BOULDER, Source: Dissertation Abstracts International, Volume: 32-02, Section: B, page: 1134
- +
 [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 [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
  
-[5] Czekala et al. (2001), Discrimination of cloud and rain liquid water path by groundbased polarized microwave radiometry, Geophy. Res. Lett., DOI: 10.1029/2000GL012247+[5] http://cetemps.aquila.infn.it/mwrnet/main_files/whatisMWRnet.html 
 + 
 +[6] Westwater, E.R., C. Mätzler, S. Crewell (2004) A review of surface-based microwave and millimeter-wave radiometric remote sensing of the troposphere. Radio Science Bulletin, No. 3010, September 2004, 59-80, 
 + 
 +[7] Westwater, E. R., S. Crewell, C. Mätzler, and D. Cimini, 2006: Principles of Surface-based Microwave and Millimeter wave Radiometric Remote Sensing of the Troposphere, Quaderni Della Societa Italiana di Elettromagnetismo, 1(3), September 2005, 50-90.  
 + 
 +[8] Final report of the COST action EG-Climet, http://cfa.aquila.infn.it/wiki.eg-climet.org/index.php5/Microwave_radiometer 
 + 
 +[9] Czekala et al. (2001), Discrimination of cloud and rain liquid water path by groundbased polarized microwave radiometry, Geophy. Res. Lett., DOI: 10.1029/2000GL012247
  
-[6] Bennartz, R., and P. Bauer (2003), Sensitivity of microwave radiances at 85–183 GHz to precipitating ice particles, Radio Sci., 38(4), 8075, doi:10.1029/2002RS002626.+[10] Bennartz, R., and P. Bauer (2003), Sensitivity of microwave radiances at 85–183 GHz to precipitating ice particles, Radio Sci., 38(4), 8075, doi:10.1029/2002RS002626.
  
-[7| Kneifel et al. (2010), Snow scattering signals in ground-based passive microwave radiometer measurements, J. Geophys. Res., DOI: 10.1029/2010JD013856+[11] Kneifel et al. (2010), Snow scattering signals in ground-based passive microwave radiometer measurements, J. Geophys. Res., DOI: 10.1029/2010JD013856
  
  
  
   
instruments/hatpro/hatpro.txt · Last modified: 2021/01/22 22:17 by 127.0.0.1