instruments:hatpro:hatpro
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instruments:hatpro:hatpro [2016/05/24 15:57] – stefan | instruments:hatpro:hatpro [2016/06/11 21:58] – susanne | ||
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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 | + | Ground-Based radiometer for the determination of temperature profiles |
+ | |||
+ | 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 [9] but also to constrain the columnar amount of snow and ice particles from space [10] and from the ground [11]. |
+ | {{: | ||
+ | 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:// | ||
+ | ===== Design and Calibration ===== | ||
+ | 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, | ||
+ | |||
+ | Usually ground-based radiometers are also equipped with environmental sensors (rain, temperature, | ||
- | {{ :instruments:hatpro: | + | {{:stuff:mwr_design.png|Schematic diagram |
- | Microwave spectrum: The black lines show the spectrum from the view of a ground-based receiver, | + | Fig. 4: Schematic diagram |
+ | After being received at the antenna | ||
- | ===== Design | + | ===== Calibration |
+ | 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, | ||
- | Basically, the radiometers have the general form of the design. Radiometer is consisted of few blocks: antenna system, microwave radiothermal receiver, recording and storage devices and radioengineering system for the transmission of obtained data to the processing step. Here is short description of several major blocks of radiometers: | + | The temperatures |
- | + | ||
- | - The antenna block receives radiation propagating in free space. This module transforms these electromagnetic waves into the oscillation modes guided in a transmission line. | + | |
- | - 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 | + | |
- | + | ||
- | Also, depending on the particular characteristics | + | |
- | + | ||
- | + | ||
- | {{ : | + | |
===== | ===== | ||
- | 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] Westwater, Edgeworth Rupert, 1970: Ground-Based Determination of Temperature Profiles by Microwaves. PH.D. Thesis, UNIVERSITY OF COLORADO AT BOULDER, Source: Dissertation Abstracts International, | ||
+ | |||
+ | [4] Passive Microwave Remote Sensing of the Earth, Physical Foundations, | ||
+ | |||
+ | [5] http:// | ||
+ | |||
+ | [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, | ||
+ | |||
+ | [8] Final report of the COST action EG-Climet, http:// | ||
+ | |||
+ | [9] Czekala et al. (2001), Discrimination of cloud and rain liquid water path by groundbased polarized microwave radiometry, Geophy. Res. Lett., DOI: 10.1029/ | ||
+ | |||
+ | [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: | ||
+ | |||
+ | [11] 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