Millimeter-wave Radiometer Research Articles

УТРОИТЕЛЬ ЧАСТОТЫ НА ДИОДАХ С БАРЬЕРОМ ШОТТКИ В ПРИЕМНИКЕ 3-ММ ДИАПАЗОНА ДЛЯ ИССЛЕДОВАНИЙ ЛИНИЙ ИЗЛУЧЕНИЯ АТМОСФЕРНЫХ ГАЗОВ

A Schottky diode frequency tripler for the 3-mm receiver system designed for observation of ozone and carbon monoxide spectral lines at frequencies 110.836 and 115.271 GHz, respectively, is developed. The used varactor parameters are investigated and its limiting values of frequency tripling efficiency in the 3-mm wavelengths calculated. A design of the multiplier, which allows to realize close to the calculated levels of frequency conversion efficiency is proposed. The characteristics of the developed multiplier are investigated within the frequency range 109-136 GHz. The output power of 8 mW is obtained at 132 GHz with about 62 mW pumping power. The tripler efficiency, output power and operating current at the desired frequency for atmospheric receiver of 112.5 GHz were measured. The highest efficiency (18 %) has been realized at this frequency with 15 mW input power. The values of the input power, operating current and reverse bias of the developed frequency tripler required for optimal receiver performance for observation of the emission lines of atmospheric gases have been determined. Key words: frequency tripler , receiver for investigation of atmospheric gases, frequency tripling efficiency, input power, output power Manuscript submitted 07.08.2014 Radio phys. radio astron. 2015, 20(1): 86-93 REFERENCES 1. FORKMAN, P., CHRISTENSEN, O. M., ERIKSSON, P., URBAN, J. and FUNKE, B., 2012. Six years of mesospheric CO estimated from ground-based frequency-switched microwave radiometry at 57° N compared with satellite instruments. Atmos. Meas. Tech. vol. 5, no. 11, pp. 2827–2841. DOI: https://doi.org/10.5194/amtd-5-3909-2012 2. RAFFALSK, I. U., BERG, H., HOCHSCHILD, G. and KOPP, G., 2002. 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Radiometric Information Content for Water Vapor and Temperature Profiling in Clear Skies Between 10 and 200 GHz

Atmospheric profiles of water vapor and temperature can be estimated using appropriate retrieval algorithms based on radiometric measurements and atmospheric statistics. Radiometric measurements at multiple frequencies contribute information to profile retrieval, although at some frequencies the information they provide can be highly correlated with that at other frequencies due to similar sensitivities to changes in atmospheric pressure, temperature, and water vapor mixing ratio as a function of altitude. The goal for profile retrieval is to obtain as many independent measurements as possible, both to maximize the vertical resolution and to minimize the retrieval error of the profile. The goal of this study is to determine sets of frequencies in the range from 10 to 200 GHz that provide the largest amount of mutually independent information on water vapor and temperature profiles from ground and airborne instruments for clear sky measurements. Results of such a study are important and useful for frequency selection and design of microwave and millimeter-wave radiometers for humidity and temperature profiling. A branch and bound feature selection algorithm has been used to determine sets of frequencies between 10 and 200 GHz that have the greatest number of degrees of freedom (DOF) for water vapor and temperature retrieval. In general, it has been found that the frequency ranges of 20–23, 85–90, and 165–200 GHz are useful for water vapor profile retrieval, whereas the frequency ranges of 55–65 and 116–120 GHz are useful for temperature profile retrieval. Finally, an analysis has been performed to determine the impact of measurement uncertainty on the number of DOF of measurement and also on the vertical resolution. It was also found that vertical resolution is directly related to the number of DOF.

A New 2-Dimensional Millimeter Wave Radiation Imaging System Based on Finite Difference Regularization

Synthetic aperture imaging radiometer (SAIR) has the potential to meet the spatial resolution requirement of passive millimeter remote sensing from space. A new two-dimensional (2-D) imaging radiometer at millimeter wave (MMW) band is described in this paper; it uses a one-dimensional (1-D) synthetic aperture digital radiometer (SADR) to obtain an image on one dimension and a rotary platform to provide a scan on the second dimension. Due to the ill-posed inverse problem of SADR, we proposed a new reconstruction algorithm based on Finite Difference (FD) regularization to improve brightness temperature images. Experimental results show that the proposed 2-D MMW radiometer can give the brightness temperature images of natural scenes and the FD regularization reconstruction algorithm is able to improve the quality of brightness temperature images.

Uncorrelated Phase Noise Analysis for Millimeter-Wave Radiometer Imager Frequency Synthesizer

In this paper, a nontrivial uncorrelated phase noise analysis is proposed for frequency synthesizer of a passive millimeter-wave Synthetic Aperture Interferometric Radiometer (SAIR) imager named BHU-2D-U designed for concealed weapon detections on human bodies with high imaging rates. This synthesizer provides local oscillators both for millimeter-wave front-ends and intermediate frequency IQ demodulators for the receivers. The influence of synthesizer uncorrelated phase noise in different offset frequency ranges on the visibility phase errors have been systematically investigated with phase noise mismatch requirements drawn. Integrated RMS phase error has been applied to establish uncorrelated phase noise requirements for visibility error control. Measurement results have proved that uncorrelated phase noise does exist among synthesizer output pairs, and the previously defined requirements are achieved with imaging results proposed. In conclusion, the uncorrelated phase noise effects on SAIR visibility errors have been concretized to phase noise design requirements, which have been realized by synthesizer design. DOI : http://dx.doi.org/10.11591/telkomnika.v12i2.3844

A Phase Noise Analysis Method for Millimeter-Wave Passive Imager BHU-2D-U Frequency Synthesizer

A nontrivial phase noise analysis method is proposed for frequency synthesizer of a passive millimeter-wave synthetic aperture interferometric radiometer (SAIR) imager for concealed weapon detections on human bodies with high imaging rates. The frequency synthesizer provides local oscillator signals for both millimeter-wave front ends and intermediate frequency IQ demodulators for the SAIR system. The influence of synthesizer phase noise in different offset frequency ranges on the visibility phase errors has been systematically investigated with noise requirements drawn, and the integrated RMS phase error could represent uncorrelated phase noise effects in the most critical offset frequency range for visibility error control. An analytical phase noise simulation method is proposed to guide synthesizer design. To conclude, the phase noise effects on SAIR visibility errors have been concretized to noise design requirements, and good agreements have been observed between simulation and measurement results. The frequency synthesizer designed has been successfully in operation in BHU-2D-U system.

Characteristic analysis of aspheric quasi-optical lens antenna in millimeter-wave radiometer imaging system

Quasi-optical imaging systems require low blurring effect and large depth of focus (DOF) to get an acceptable sharpness of the image. To reduce aberration-limited blurring, the aspheric convex plano lenses with an aperture diameter of 350 mm are designed in W-band. We analyzed theoretically and experimentally the millimeter-wave band lens characteristics, such as beam spot size, spatial resolution (SR), and DOF, via f-number. It is first used to verify the DOF through f-number in the system-level test with the developed W-band radiometer imaging system. We have confirmed that the larger f-number of quasi-optical lens leads to a larger DOF but a lower SR.

The first aerosol indirect effect quantified through airborne remote sensing during VOCALS-REx

Abstract. The first aerosol indirect effect (1AIE) is investigated using a combination of in situ and remotely-sensed aircraft (NCAR C-130) observations acquired during VOCALS-REx over the southeast Pacific stratocumulus cloud regime. Satellite analyses have previously identified a high albedo susceptibitility to changes in cloud microphysics and aerosols over this region. The 1AIE was broken down into the product of two independently-estimated terms: the cloud aerosol interaction metric ACIτ =dlnτ/dlnNa|LWP , and the relative albedo (A) susceptibility SR-τ =dA/3dlnτ|LWP, with τ and Na denoting retrieved cloud optical thickness and in situ aerosol concentration respectively and calculated for fixed intervals of liquid water path (LWP). ACIτ was estimated by combining in situ Na sampled below the cloud, with τ and LWP derived from, respectively, simultaneous upward-looking broadband irradiance and narrow field-of-view millimeter-wave radiometer measurements, collected at 1 Hz during four eight-hour daytime flights by the C-130 aircraft. ACIτ values were typically large, close to the physical upper limit (0.33), with a modest increase with LWP. The high ACIτ values slightly exceed values reported from many previous in situ airborne studies in pristine marine stratocumulus and reflect the imposition of a LWP constraint and simultaneity of aerosol and cloud measurements. SR-τ increased with LWP and τ, reached a maximum SR-τ (0.086) for LWP (τ) of 58 g m−2 (~14), and decreased slightly thereafter. The 1AIE thus increased with LWP and is comparable to a radiative forcing of −3.2– −3.8 W m−2 for a 10% increase in Na, exceeding previously-reported global-range values. The aircraft-derived values are consistent with satellite estimates derived from instantaneous, collocated Clouds and the Earth's Radiant Energy System (CERES) albedo and MOderate resolution Imaging Spectroradiometer (MODIS)-retrieved droplet number concentrations at 50 km resolution. The consistency of the airborne and satellite estimates, despite their independent approaches, differences in observational scales, and retrieval assumptions, is hypothesized to reflect the ideal remote sensing conditions for these homogeneous clouds. We recommend the southeast Pacific for regional model assessments of the first aerosol indirect effect on this basis. This airborne remotely-sensed approach towards quantifying 1AIE should in theory be more robust than in situ calculations because of increased sampling. However, although the technique does not explicitly depend on a remotely-derived cloud droplet number concentration (Nd), the at-times unrealistically-high Nd values suggest more emphasis on accurate airborne radiometric measurements is needed to refine this approach.

Design and Implementaion of Data Processing and Control Module in Millimeter-Wave Radiometer

This paper introduces a data processing and control module used for a millimeter-wave radiometer. The STM32F103ZET6 is chosen as an embedding control unit for real-time control and data acquisition and processing，and 8-inch touch LCD screen is used for display and input. The data processing and control unit in total-power radiometer with a Dicke-type switch are presented. The hardware structure and software flowchart are designed for this embedding system. The units effectively adjust physical temperature of the radiometer to acquire appropriate output in the radiometer system without inexpensive commercially available parts.

MMW Radiometric Image Feature Extraction Method of Concealed Objects Based on Watershed Algorithm

Because of all-time, all-weather ability to work and strong penetration, millimeter-wave radiometer is used to inspect concealed objects hidden under clothing. Due to the restrictions of antenna, equipment and environment, the resolution of image is low and the contours of concealed objects are not clear. To improve the quality of radiometric images and the accuracy of edge detection, we firstly process the image using threshold segmentation, then, a method of combining morphology self-adaptive filter and watershed algorithm is proposed to do the further processing and feature extraction. The experiment results indicate that morphology self-adaptive algorithm and watershed algorithm can complete the edge extraction of the concealed objects well with the real objects.

밀리미터파 복사계의 제작

Abstract We have manufactured a close range Dicke type radiometer which consists of two stage low noise amplifier and diode detector. Frequency range of this system is 35 GHz. And this is used for studying temperature calibration on specific objects. We have present millimeter-wave radiometer's thermal calibration method and its characteristics. From absolute temperature 299K to 309K, in proportion to increase temperature, output voltages are linearly increased. In this case, undefined objects can be measured thermal noise temperature relatively. Overall from absolute temperature 214K to 309K, we have obtained relation of temperature and output voltage;V= 0.03601K - 10.70517. Key Words : Dicke type radiometer, Millimeter-wave radiometer, Thermal noise, Calibration * 정회원, 상지대학교 이공대학 응용물리전자학과접수일자 2010.9.4, 수정완료 2012.5.15게재확정일자 2012.6.8.Received: 4 September, 2010, Revised: 15 May, 2012Accepted: 8 June, 2012 * Corresponding Author:kookim@dongguk.eduDept. of Applied Physics & Electronics, Sangji University, Korea

High dynamic range 140–220 GHz radiometer using dual-channel superheterodyne receivers

A millimetre-wave radiometer in the range 140–220 GHz using dual-channel superheterodyne receivers is described. The dynamic range of the radiometer is estimated to be 163 dB. The linearity of the receiver is traceable to a low-frequency voltage ratio standard. A 10–120 dB synthesised rotary vane attenuator has been measured with uncertainties of 0.022–0.90 dB at 220 GHz to verify the accuracy of the radiometer.

Frequency Estimation of Human Presence Detection Signals From a Scanning-Beam Millimeter-Wave Correlation Radiometer

The scanning-beam millimeter-wave correlation radiometer has recently been applied to human presence detection and classification. The natural frequency of the scanning-beam correlation radiometer signal, called the fringe frequency, results from human presence in the scanning beam and must be known in order to filter the signal and provide the best possible radiometric sensitivity. This letter presents new results in estimating the fringe frequency of a 27.4-GHz scanning-beam correlation radiometer by comparing different spectral estimation techniques, including CLEAN, RELAX, PHD, MUSIC, and ESPRIT. Experiments were performed with a human placed beyond the mean detection range of the sensor, resulting in signal power levels below the average power expected in an operational environment. Results show good performance for the CLEAN and RELAX algorithms at fringe frequencies in the range of 15-60 Hz and for the MUSIC and ESPRIT algorithms at fringe frequencies in the range of 60-155 Hz.

Millimeter-wave radiometer diagnostics of harmonic electron cyclotron emission in the Levitated Dipole Experiment

A 110/137 GHz radiometer pair with collimated antenna pattern is being used to diagnose optically thin harmonic electron cyclotron emission from hot electrons in LDX. Signal levels of 0.1-1 keV and 110/137 ratios of 2-4 stationary with ECRH power have been observed. The large plasma core magnetic field gradient causes all relevant harmonics to be simultaneously viewed over a angle(k,B) angular range of 0°-90° representing a unique geometry for interpretation of ECE in terms of hot electron temperature and density.

Single scattering from frozen hydrometeors at microwave frequencies

Scattering of electromagnetic waves from homogeneous or coated spheres can be computed in a mathematically exact way using the Mie theory. Therefore, for many approaches in remote sensing, frozen hydrometeors are parameterized as ice spheres. However, many frozen hydrometeors have non-spherical overall shapes and lack a spherically symmetric internal structure. They exist in a huge variety of shapes and exhibit different mixtures of ice, water and air. Therefore it is desirable to accurately compute scattering from non-spherical particles in order to clearly understand the effect the shape of a hydrometeor has on its scattering pattern. In this study, single scattering parameters like scattering cross section, absorption cross section, and asymmetry factor were calculated for frozen hydrometeors using the Discrete Dipole Approximation (DDA). The particles were modeled as hexagonal plates, columns, needles and dendrites by applying known dimensional relationships. The calculations were carried out over a wide range of centimeter and millimeter-wavelengths (1 GHz to 300 GHz), since millimeter-wave radiometers are highly sensitive to scattering by frozen hydrometeors in the atmosphere. The study results show that for size parameters < 1 (a ratio between wavelength and particle size) the scattering cross section of randomly orientated ice crystals is close to that of an equal volume ice sphere. Absorption cross section and asymmetry factor of non-spherical particles however are up to twice as high as that of equal volume ice spheres. Further the influence of the assumed model for the refractive index of ice at microwave wavelengths on the scattering parameters is investigated.

Comparison of Ground-Based Millimeter-Wave Observations and Simulations in the Arctic Winter

During the Radiative Heating in Underexplored Bands Campaign (RHUBC), held in February-March 2007, three millimeter-wave radiometers were operated at the Atmospheric Radiation Measurement Program's site in Barrow, Alaska. These radiometers contain several channels located around the strong 183.31-GHz water vapor line, which is crucial for ground-based water-vapor measurements in very dry conditions, typical of the Arctic. Simultaneous radiosonde observations were carried out during conditions with very low integrated-water-vapor (IWV) content (< 2 mm). Observations from the three instruments are compared, accounting for their different design characteristics. The overall agreement during RHUBC among the three instruments and between instruments and forward model is discussed quantitatively. In general, the instrument cross-validation performed for sets of channel pairs showed agreement within the total expected uncertainty. The consistency between instruments allows the determination of the IWV to within around 2% for these dry conditions. Comparisons between these data sets and forward-model simulations using radiosondes as input show spectral features in the brightness-temperature residuals, indicating some degree of inconsistency between the instruments and the forward model. The most likely cause of forward-model error is systematic errors in the radiosonde humidity profiles.

The Performance Analysis of Digital Millimeter-Wave Radiometer

Digital millimeter-wave radiometer (DMMWR) has advantages such as simple structure and good stability, of which a wide-band, high speed analog-to-digital converter (ADC) is the key component. However the unavoidable impairments of ADC in DMMWR degrade the sensitivity and accuracy, the main performance parameters of DMMWR. This paper investigates the sensitivity of DMMWR by deriving an expression for the noise-equivalent sensitivity based on the signal statistical property. Also, it analyzes the accuracy of DMMWR by establishing the calibration equation between output signal power and system noise temperature. During the experiment, the methods of multi-point calibration and curve fitting are introduced to calibrate the nonlinearity and fit the calibration equation of DMMWR, respectively. The experimental results show that the sensitivity expression gives predictions in agreement with experimental results and multi-point calibration can improve the measurement accuracy of DMMWR.

Statistical Distribution of Visibilities in Digital Aperture Synthesis Radiometry

The statistical characteristics of visibilities measured by digital complex correlators in aperture synthesis radiometry are investigated. First, the analytic probability density function of visibilities is derived under the assumption that the successive samples are Gaussian distributed and statistically independent. However, in practice, the assumption may be not satisfied due to non-Nyquist sampling and quantizing. Then, to account for such impacts, an effective sample size is proposed. By compensating with it, the statistical distribution of visibilities is well represented in closed form. The experimental results by using an aperture synthesis millimeter-wave radiometer demonstrate the validity of the improved distribution. The results of this letter can be applied to sensitivity estimation and high-accuracy image reconstruction in digital aperture synthesis radiometry.

Key Indexes Analysis of Three Beams Conical Scan MMW Radiometer

Building on a mathematical model of a single beam millimeter wave (MMW) radiometer on a hi-tech bomb, system parameters are proposed and simulated for a three beam MMW radiometer. Scanning rate, falling rate and other parameters are put forward in the context of a novel conical scan MMW detector. The demodulated signals of detecting a target are simulated. With this approach the target radial center positioning accuracy can be improved. The simulation results indicate that the radiometer has favorable performances, such as a wide range of detection, high radial positioning accuracy and reacquisition target ability in the most adverse condition that the target’s radial movement is outwards.

Precipitating Snow Retrievals from Combined Airborne Cloud Radar and Millimeter-Wave Radiometer Observations

Abstract An algorithm for retrieving snow over oceans from combined cloud radar and millimeter-wave radiometer observations is developed. The algorithm involves the use of physical models to simulate cloud radar and millimeter-wave radiometer observations from basic atmospheric variables such as hydrometeor content, temperature, and relative humidity profiles and is based on an optimal estimation technique to retrieve these variables from actual observations. A high-resolution simulation of a lake-effect snowstorm by a cloud-resolving model is used to test the algorithm. That is, synthetic observations are generated from the output of the cloud numerical model, and the retrieval algorithm is applied to the synthetic data. The algorithm performance is assessed by comparing the retrievals with the reference variables used in synthesizing the observations. The synthetic observation experiment indicates good performance of the retrieval algorithm. The algorithm is also applied to real observations from the Wakasa Bay field experiment that took place over the Sea of Japan in January and February 2003. The application of the retrieval algorithm to data from the field experiment yields snow estimates that are consistent with both the cloud radar and radiometer observations.

Intercomparison of Odin–SMR ozone profiles with ground-based millimetre-wave observations in the Arctic, the mid-latitudes, and the tropics

The sub-millimetre radiometer (SMR) on board the Odin satellite measures signatures of ozone in two bands centred at 501.8 and 544.6 GHz. From the measurements, ozone volume mixing ratio profiles in the stratosphere and lower mesosphere are retrieved using the Optimal Estimation Method. In this paper, the ozone profiles measured by Odin–SMR (level-2 data ver. 2.1 and 2.0, respectively) are compared to measurements taken by ground-based millimetre wave radiometers in the Arctic; at Kiruna, Sweden; in the mid-latitudes on the Zugspitze, Germany; and in the tropics at Mérida, Venezuela. The Kiruna Microwave Radiometer (KIMRA) covers the frequency range 195–224 GHz, and the Millimeter Wave Radiometer MIRA 2, which was operated on the Zugspitze and at Mérida, measures in the frequency band 268–281 GHz. From the measurements, ozone profiles in the vertical range between approximately 15–65 km were retrieved using the Optimal Estimation Method. Since the ground-based measurements have a lower vertical resolution than those of Odin the latter were degraded using the averaging kernels of the ground-based retrievals. The comparison of the resulting profiles to the ground-based data enables the identification of biases in the Odin measurements and their possible latitudinal variation. In general, a good agreement between satellite and ground-based measurements for the 501.8 GHz band was found in the stratosphere except for a negative bias in the Odin data of about 10–15% in the tropical measurements. The Odin measurements taken at 544.9 GHz yielded systematically 20–30% lower ozone mixing ratios in the middle stratosphere than the ground-based measurements at all sites. PACS No.: 92.60.hd