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--- instruments:hatpro:hatpro [2016/06/11 21:58] – susanne
+++ instruments:hatpro:hatpro [2018/07/23 12:51] – andreas
@@ Line 1: / Line 1: @@
 **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:sunhat:sunhat|SUNHAT]] on [[sites:barbados|Barbados]]
   * [[instruments:snohat:snohat|SNOHAT]] at the [[sites:ufs|Schneefernerhaus observatory]] (Mt. Zugspitze)
+  * [[instruments:sunhat:sunhat|SUNHAT]] on [[sites:barbados|Barbados]]
 ===== Introduction =====
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 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.
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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 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   =====
 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.