Multiangle method for temperature measurement of biological tissues by microwave radiometry

A new approach for deriving the temperature distribution in biological tissues of microwave radiometry is proposed. It consists in the measurement of the thermal radiation of the body, at a given frequency, as a function of the observation angle, for two mutually orthogonal polarizations. Theoretically, this method yields results comparable to those obtained with the multispectral method. In order to derive the relations between the body temperature and the emitted thermal signal, the biological body is modeled by a set of parallel planar layers, each characterized by constant permittivity and temperature. It is demonstrated that for all practical purposes the radiation pattern of the antenna may be approximated by that of an unbounded plane wave.<>     

Improved recognition of thermal structures by microwave radiometry

A radiometric system for medical applications, including a set of six probes, facilitates the positioning of the probes and improves the precision in their location. An example of an experiment and of signal processing is shown which improves the recognition of the thermal structure.     

An example of thermometry in volume by microwave radiometry

A method of determination of the size D depth z and temperature T0+ΔT of a cylindrical thermal structure embedded in an homogeneous lossy material, in the present case, water, is presented. A microwave radiometric image at 3 GHz points out the location of the thermal structure; its threshold provides the diameter D of the structure. The depth z derives from the ratio of the maximal radiometric intensities at 1.5 and 3 GHz. The combination of D, z and of the radiometric intensities gives ΔT     

Correlations between slant wet delays measured by microwave radiometry

We present an analysis of the correlation between the atmospheric slant wet delays in different directions using data from a microwave radiometer. The correlations between wet delays observed in different directions using different temporal constraints are compared to a model derived from theories of turbulence. The agreement between the model and the radiometer data was good, and the average squared difference between zenith mapped slant wet delays could be predicted with an accuracy of 0.01-0.04 cm/sup 2/. Our analysis shows a large short-term variability which variance has a seasonal dependence of about /spl plusmn/26%, largely depending on the refractivity structure constant C/sub n/. We also demonstrate how the model can be used to characterize the stability of a microwave radiometer.     

Visibility of local thermal structures and temperature retrieval by microwave radiometry

For the first time, the geometrical characteristics (depth and size) and the temperature of a local thermal volume located in a homogeneous lossy material can be deduced from radiometric data. An example devoted to physical models (the lossy material is water) is based on the processing of radiometric data at 1.5 and 3 GHz.     

On the possibility of detecting avalanche victims by microwave radiometry

An experimental investigation has been made of the possibility of using a microwave radiometer to find humans covered by snow. When a radiometer operating at 1.4 GHz was moved along a track it registered a highly fluctuating radiation temperature of the snow covered ground. The increase in temperature when the radiometer passed over a human was so small that detection in general was impossible.     

Satellite microwave radiometry of forest and surface types inFinland

10.7-, 18-, and 37-GHz data from the Nimbus-7 Scanning Multichannel Microwave Radiometer (Nimbus-7 SMMR) were used to investigate the microwave response to different surface and forest types. SMMR data for the fall seasons of 1978 through 1981 were compared against a digital surface type map that shows seven different surface types for southern Finland and six for northern Finland. For each land-cover category, the brightness temperature behavior as a function of frequency and polarization was determined. The precision of the results is evaluated, and they are compared to other published results. The discrimination of land-cover categories using the brightness temperature is discussed     

A physical model to determine snowfall over land by microwave radiometry

Falling snow is an important component of global precipitation in extratropical regions. This paper describes the methodology and results of physically based retrievals of snow falling over land surfaces. Because microwave brightness temperatures emitted by snow-covered surfaces are highly variable, precipitating snow above such surfaces is difficult to observe using window channels that occur at low frequencies (/spl nu/<100 GHz). Furthermore, at frequencies /spl nu//spl les/37 GHz, sensitivity to liquid hydrometeors is dominant. These problems are mitigated at high frequencies (/spl nu/>100 GHz) where water vapor screens the surface emission, and sensitivity to frozen hydrometeors is significant. However, the scattering effect of snowfall in the atmosphere at those higher frequencies is also impacted by water vapor in the upper atmosphere. The theory of scattering by randomly oriented dry snow particles at high microwave frequencies appears to be better described by regarding snow as a concatenation of "equivalent" ice spheres rather than as a sphere with the effective dielectric constant of an air-ice mixture. An equivalent sphere snow scattering model was validated against high-frequency attenuation measurements. Satellite-based high-frequency observations from an Advanced Microwave Sounding Unit (AMSU-B) instrument during the March 5-6, 2001 New England blizzard were used to retrieve snowfall over land. Vertical distributions of snow, temperature, and relative humidity profiles were derived from the Mesoscale Model (MM5) cloud model. Those data were applied and modified in a radiative transfer model that derived brightness temperatures consistent with the AMSU-B observations. The retrieved snowfall distribution was validated with radar reflectivity measurements obtained from a ground-based radar network.     

The main results of cloud and rain remote sensing by multichannel microwave radiometry

The basic results have been considered for multiwave remote sounding of the troposphere with clouds and rain from ground-based station in the zenith direction. The radio wave scattering by rain drops as well as variation of vapour content in the atmosphere during measurements are taken into account when processing of the experimental data. A separation of the complete attenuation in clouds with rain has been made over three components: due to vapour, cloud and rain. A relation is considered of millimeter and centimeter wave attenuation in clouds with rain between each other and with the rain intensity. A behaviour of the relation of attenuation structural functions is explained. The Diagnostic problems of millimeter wave attenuation are considered.     

The measurement of rainfall in Papua New Guinea,and its effect on microwave propagation

A programme of measurement on rainfall characteristics has been commenced at Lae, Papua New Guinea, using pluviometers, tipping bucket rain-gauges and a rapid-response rain-gauge. Pluviographs extending over many years have been analysed by computer to give data on general rain conditions and on the probability of rainfall intensity exceeding particular levels. The resultant distribution compares well with the empirical formula of Moupfouma, and corresponding parameters are given. Simultaneous measurements are also being made on the 12 GHz signal level variation from the Aussat television signal, and on the attenuation on a 10 GHz terrestrial link.     

Plant water content and temperature of the Amazon forest fromsatellite microwave radiometry

An attempt is made to derive the evolution of the temperature and the water status of the Amazon forest canopy from satellite microwave radiometry. The Nimbus-7 Scanning Multichannel Microwave Radiometer (SMMR) temperature-corrected tapes data are analyzed for the 6.6, 10.7, 18, and 37 GHz frequencies, at daytime and nighttime, over a zone near Manaus (3°S, 60°W), Brazil. Two periods are investigated: the wet (April-May) and dry (July-August) seasons of 1985. After separating forest- from river-contaminated pixels, atmospheric corrections are performed for water vapor, clouds, and rain, using surface and satellite data. Algorithms are developed to model the microwave thermal emission of vegetation following a continuous approach and a discrete approach. A sensitivity study is performed in order to determine which frequencies are relevant to retrieve land surface parameters. The models are then used along with an optimization procedure so as to carry out the inversion of the canopy structure parameters. The vegetation temperature and water content are retrieved through the continuous model     

Interferometric synthetic aperture microwave radiometry for theremote sensing of the Earth

Interferometric aperture synthesis is presented as an alternative to real aperture measurements of the Earth's brightness temperature from low Earth orbit. The signal-to-noise performance of a single interferometric measurement is considered, and the noise characteristics of the brightness temperature image produced from the interferometer measurements are discussed. The sampling requirements of the measurements and the resulting effects of the noise in the measurements on the image are described. The specific case of the electronically steered thinned array radiometer (ESTAR) currently under construction is examined. The ESTAR prototype is described in detail sufficient to permit a performance evaluation of its spatial and temperature resolution. Critical aspects of an extension of the ESTAR sensor to a larger spaceborne system are considered. Of particular important are the number and placement of antenna elements in the imaging array     

Remote sensing of atmospheric water content from satellites using microwave radiometry

Analysis is presented which substantiates the high correlation achieved in relating integrated water vapor and liquid water to brightness temperatures at frequencies near the 22.235 GHz water vapor line. The influence of atmospheric and surface variability is shown to be minimal over low emissivity sea surfaces. Determination of atmospheric water content using regression techniques is shown to follow directly from radiation transfer theory. Satellite data from the Nimbus-E Microwave Spectrometer (NEMS) aboard Nimbus-5 are compared with radiosonde water vapor measurements and cloud images recorded by the Temperature Humidity Infrared Radiometer aboard Nimbus 5.     

RFI detection and mitigation for microwave radiometry with an agile digital detector

A new type of microwave radiometer detector has been developed that is capable of identifying high and low levels of radio-frequency interference (RFI) and of reducing or eliminating its effect on the measured brightness temperatures. High-level, localized RFI can be easily identified by its unnatural appearance in brightness temperature imagery. Low-level or persistent RFI can be much more difficult to identify and filter out. The agile digital detector (ADD) can discriminate between RFI and natural thermal emission signals by directly measuring higher order moments of the signal than the variance that is traditionally measured. After detection, the ADD then uses spectral filtering methods to selectively remove the RFI. ADD performance is experimentally verified in controlled laboratory tests and in the field near a commercial air traffic control radar. High-level RFI is easily identified and removed. Very low level RFI contamination, with power levels as low as the radiometric measurement uncertainty of the radiometer, is also shown to be reliably detected and removed.     

Frequency and polarisation scaling of microwave attenuation during rainfall

Measurements are presented from eastern Canada of the polarisation-dependent ratio of microwave attenuation due to rainfall for vertical and horizontal linear polarisations, and of the frequency-dependent ratio of attenuation for a given polarisation. The exponent of the usual power law of frequency scaling of attenuation is 1.93±0.15 (SD) in the 11?17 GHz frequency range.     

影响地面雷达测高精度的因素

针对某型三坐标地面雷达,对影响地面雷达测高精度的主要因素进行了分析。基于阵地地形、电磁环境、杂波环境、大气环境和人为导致的系统异常等因素,分析了地面雷达测高误差产生的原因,评估了多种因素对测高精度的影响程度,提出了在实际应用中规避影响因素以改善地面雷达测高精度的建议。     

The vertical resolution of ground-based microwave radiometersanalyzed through a multiresolution wavelet technique

The spatial resolution of a ground-based microwave radiometer is analyzed through a multiresolution wavelet transform. This technique allows us to compare the ability of the instrument to detect perturbations in a profile under different observing configurations and different noise levels. The use of a wavelet transform applied to performance indicators enables us to isolate the altitude and scale of the perturbation providing an unambiguous definition of resolution. A suitable ensemble of channels and view angles can then be selected to optimize the performance at different altitudes and different resolutions. Several angle/channel configurations are simulated. Among the configurations examined, a scanning system with only one channel offered a resolution comparable to a multichannel system for boundary layer sensing. The simulation suggests that increasing the bandwidth in the multichannel system improves the performance of the fixed view configuration. For investigation above 1 km, a multichannel system with fixed angle seems to offer a better performance at a coarser resolution     

Self-consistency of polarization diversity measurement of rainfall

Polarization diversity measurements of rainfall, namely the reflectivity factor, differential reflectivity, and specific differential propagation phase, vary in a constrained three-dimensional space. Algorithms are derived to quantify this self-consistency of measurements. In particular, estimation of the specific differential propagation phase shift based on reflectivity and differential reflectivity is analyzed in detail. Theoretical simulation as well as radar observations of rainfall at S (CSU-CHILL) and C (Polar 55C) bands are used to demonstrate that the range profiles of differential propagation shift can be constructed from measurements of reflectivity and differential reflectivity