instruments:hatpro:hatpro
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===== Introduction ===== | ===== Introduction ===== | ||
+ | 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, | ||
- | The atmosphere in the [[https:// | + | Using the [[https:// |
For weather and climate monitoring, microwave radiometers are operated from space [1] [2] as well as from the ground [3]. As [[https:// | For weather and climate monitoring, microwave radiometers are operated from space [1] [2] as well as from the ground [3]. As [[https:// | ||
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{{: | {{: | ||
- | [[http:// | + | Fig. 1: [[http:// |
===== History of microwave radiometer measurements ===== | ===== 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:// | ||
- | The first operational microwave radiometer was designed by [[https:// | + | Soon after satellites were first used for observing the atmosphere, MW radiometers became part of their instrumentation. In 1962 the [[https:// |
- | Soon after satellites were first used for observing | + | Here we could keep the graphic from the original article |
+ | https:// | ||
+ | Fig. 2 | ||
===== Principle of operation ===== | ===== Principle of operation ===== | ||
- | Solid matter | + | Solids, liquids |
+ | 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, | ||
- | In addition to gaseous absorption, scattering, absorption, and emission | + | 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]. |
- | + | {{: | |
- | + | Fig. 3: Microwave spectrum: The black lines show the simulated | |
- | {{ : | + | |
- | Microwave spectrum: The black lines show the spectrum | + | |
===== Design ===== | ===== Design ===== | ||
+ | The principal components of a microwave radiometer often follow a similar design and can be grouped into: antenna system, microwave radio-thermal receiver, recording and storage devices and a final processing unit. Usually ground-based radiometers are also equipped with environmental sensors (rain, temperature, | ||
- | Basically, the radiometers have the general form of the design. Radiometer is consisted | + | {{: |
+ | Fig. 4: Schematic diagram of a microwave radiometer. | ||
- | - The antenna block receives radiation propagating in free space. This module transforms these electromagnetic waves into the oscillation modes guided in a transmission line. | + | ===== Calibration ===== |
- | - Radiometric receiving device consists of a high-frequency amplifier, a quadratic device and a low-frequency filter. The function of a high-frequency amplifier is to amplify the received signal in every frequency band. | + | |
- | - Recording and storage devices – these parts of the system are made for recording the measured parameters. | + | |
- | Also, depending on the particular characteristics | + | The calibration |
- | + | ||
- | + | ||
- | {{ : | + | |
+ | 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. | ||
===== | ===== | ||
- | Temperature profiles can be obtained by measuring the radiation intensity, or brightness temperature, | + | The retrieval |
- | Water vapor profiles | + | |
- | The process of inverting | + | Temperature profiles are obtained by measuring along the oxygen absorption complex at 60 GHz. The emission at any altitude is proportional to local temperature |
- | + | ||
- | Along with measurements at several frequency channels, angular scans of the atmosphere provide additional information especially for the boundary layer studies. | + | |
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| {{ : | | {{ : | ||
- | Time series | + | Time series |
===== MWRnet ===== | ===== MWRnet ===== | ||
- | [[http:// | + | [[http:// |
{{ : | {{ : | ||
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===== References ===== | ===== References ===== | ||
+ | [1] Microwave Remote Sensing—Active and Passive”. By F. T. Ulaby. R. K. Moore and A. K. Fung. (Reading, Massachusetts: | ||
+ | |||
+ | [2] Thermal Microwave Radiation: Applications for Remote Sensing, C. Matzler, 2006, The Institution of Engineering and Technology, London, Chapter 1. | ||
+ | |||
+ | [3] http:// | ||
+ | |||
+ | [4] Passive Microwave Remote Sensing of the Earth, Physical Foundations, | ||
+ | |||
+ | [5] Czekala et al. (2001), Discrimination of cloud and rain liquid water path by groundbased polarized microwave radiometry, Geophy. Res. Lett., DOI: 10.1029/ | ||
+ | |||
+ | [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: | ||
+ | |||
+ | [7| Kneifel et al. (2010), Snow scattering signals in ground-based passive microwave radiometer measurements, | ||
+ | |||
- | - http:// | ||
- | - http:// | ||
- | - http:// | ||
- | - 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, | ||
- | - Cimini et al., 2009 | ||
- | - Klein and Gasiewski, 2000 | ||
- | - Eugene A. Sharkov, “Passive Microwave Remote Sensing of the Earth”, Physical Foundations, | ||
- | - http:// | ||
instruments/hatpro/hatpro.txt · Last modified: 2021/01/22 22:17 by 127.0.0.1