Millimeter-wave Propagation Model Research Articles

Improvements of the Microwave Gaseous Absorption Scheme Based on Statistical Regression and Its Application to ARMS

AbstractAn improved microwave gaseous absorption scheme based on statistical regression is proposed in this study. In the new scheme, Monochromatic Radiative Transfer Model (MonoRTM) replaces the Millimeter‐wave Propagation Model (MPM) to train the new scheme and the effect of real Spectral Response Functions is included in the training process. After the replacement, results of the new scheme are closer to observations from Advanced Technology Microwave Sounder (ATMS) onboard Suomi National Polar‐orbiting Partnership satellite in low level channels while MPM has some advantages in upper level channels. Introducing ozone absorption can cause a systematic bias but results in small standard deviations in channels with frequency 183 ± 1.8 GHz and 183 ± 1 GHz. In addition, the new scheme updates the vertical interpolation of water vapor and optimizes the vertical distribution of Planck function. These updates can reduce biases caused by vertical interpolation, especially for water vapor absorption channels. The bias associated to vertical interpolation can reach 0.25 K whereas the new scheme can decrease it to 0.003 K. To further validate the accuracy of the new scheme, we apply the new scheme to Advanced Radiative transfer Modeling System and compare simulated results to RTTOV 13.2 under 37 and 137 level (L) atmosphere (atm). Observations from ATMS onboard NOAA‐20 are used as true values. Results show that the new scheme agrees with RTTOV 13.2 well in accuracy and performs even better in upper level channels and water vapor absorption channels.

Uncertainty in simulated brightness temperature due to sensitivity to atmospheric gas spectroscopic parameters from the centimeter- to submillimeter-wave range

Abstract. Atmospheric radiative transfer models are extensively used in Earth observation to simulate radiative processes occurring in the atmosphere and to provide both upwelling and downwelling synthetic brightness temperatures for ground-based, airborne, and satellite radiometric sensors. For a meaningful comparison between simulated and observed radiances, it is crucial to characterize the uncertainty in such models. The purpose of this work is to quantify the uncertainty in radiative transfer models due to uncertainty in the associated spectroscopic parameters and to compute simulated brightness temperature uncertainties for millimeter- and submillimeter-wave channels of downward-looking satellite radiometric sensors (MicroWave Imager, MWI; Ice Cloud Imager, ICI; MicroWave Sounder, MWS; and Advanced Technology Microwave Sounder, ATMS) as well as upward-looking airborne radiometers (International Submillimetre Airborne Radiometer, ISMAR, and Microwave Airborne Radiometer Scanning System, MARSS). The approach adopted here is firstly to study the sensitivity of brightness temperature calculations to each spectroscopic parameter separately, then to identify the dominant parameters and investigate their uncertainty covariance, and finally to compute the total brightness temperature uncertainty due to the full uncertainty covariance matrix for the identified set of relevant spectroscopic parameters. The approach is applied to a recent version of the Millimeter-wave Propagation Model, taking into account water vapor, oxygen, and ozone spectroscopic parameters, though the approach is general and can be applied to any radiative transfer code. A set of 135 spectroscopic parameters were identified as dominant for the uncertainty in simulated brightness temperatures (26 for water vapor, 109 for oxygen, none for ozone). The uncertainty in simulated brightness temperatures is computed for six climatology conditions (ranging from sub-Arctic winter to tropical) and all instrument channels. Uncertainty is found to be up to few kelvins [K] in the millimeter-wave range, whereas it is considerably lower in the submillimeter-wave range (less than 1 K).

Survey of Millimeter-Wave Propagation Measurements and Models in Indoor Environments

The millimeter-wave (mmWave) is expected to deliver a huge bandwidth to address the future demands for higher data rate transmissions. However, one of the major challenges in the mmWave band is the increase in signal loss as the operating frequency increases. This has attracted several research interests both from academia and the industry for indoor and outdoor mmWave operations. This paper focuses on the works that have been carried out in the study of the mmWave channel measurement in indoor environments. A survey of the measurement techniques, prominent path loss models, analysis of path loss and delay spread for mmWave in different indoor environments is presented. This covers the mmWave frequencies from 28 GHz to 100 GHz that have been considered in the last two decades. In addition, the possible future trends for the mmWave indoor propagation studies and measurements have been discussed. These include the critical indoor environment, the roles of artificial intelligence, channel characterization for indoor devices, reconfigurable intelligent surfaces, and mmWave for 6G systems. This survey can help engineers and researchers to plan, design, and optimize reliable 5G wireless indoor networks. It will also motivate the researchers and engineering communities towards finding a better outcome in the future trends of the mmWave indoor wireless network for 6G systems and beyond.

Cost effective meter of moisture integral parameters of the atmospheric column

Continuous remote monitoring of the atmospheric physical parameters is an urgent task for solving the issues related to meteorology, climatology, artificial influence on clouds, studying the physical parameters of cloud cover etc. In the developed countries such issues are solved using science-driven technologies of millimeter wave range radiometry. They allow, in particular, quick restoration of the values of total content and effective temperature of droplet and vaporous moisture in the atmospheric column, and distinguishing the areas with crystalline, droplet or vaporous water phases.
 This work aims at substantiating, by calculation and experiment, the possibility of large-scale solving the problems of continuous remote monitoring of the studied atmospheric moisture parameters using the method of centimetre wavelength range radiometry. To determine the best pair of frequencies for restoring the atmospheric moisture parameters based on radiometric data of remote sensing the linear absorption coefficients were calculated for clear atmosphere, for cloudy atmosphere depending on the temperature of drops and for rainfalls of various intensities for 4, 12, 20, 40 and 94 GHz frequencies. In order to calculate these data, we used a well-known MPM model (Atmospheric Millimeter-Wave Propagation Model). At the same time, calculation of the altitude profiles of the atmospheric meteorological parameters was carried out based on the ERA-15 model.
 Comparison of the data obtained by calculation, taking into account the progress of the technical parameters of the serial element base, indicated a possibility of solving the above problems in the centimetre wavelength as well. The research presents a description of the diagram and technical solutions, as well as the appearance of a two-frequency radiometric system with 1.5 cm and 2.5 cm ranges created at the National Aerospace University (KhAI) on the basis of an easily accessible modern element base and full-scale tests' results. The budget-friendly focus of the described product allows for radiophysical measurement with a sensitivity of radiometers exceeding 0.01 K while ensuring the cost of small-scale production of the radio technical part of the system, comparable to the cost of TV converters commonly used in everyday life.

Indoor LOS Propagation Measurements and Modeling at 26, 32, and 39 GHz Millimeter-Wave Frequency Bands

Although the deployment of 5G networks has already started, there are still open questions regarding propagation at millimeter-wave frequency bands. Several propagation campaigns have been carried out at several bands previously identified by regulatory organizations, but due to the wide range of allocated segments of spectrum and the variety of possible propagation scenarios, more measurement campaigns are needed. In this regard, the Universidad Politécnica de Madrid (UPM) has taken millimeter-wave measurements at 26, 32, and 39 GHz bands in an indoor corridor scenario in line-of-sight (LOS) conditions with two antenna configurations (a horn antenna has been used in transmission whereas horn and omnidirectional antennas have been used in reception), and the main results are presented in this paper. The obtained path loss results have been compared with existing millimeter-wave propagation models.

Propagation properties of sub-millimeter waves in foggy conditions

The propagation of millimeter (MMW) and submillimeter (terahertz, THz) waves in the atmosphere is subject to absorptive and dispersive effects. The resulting attenuation and temporal group delay increase in cloudy and hazy weather. In this work, the effects of water droplets suspended in the air on the propagation of electromagnetic radiation in submillimeter waves are studied theoretically and experimentally. A comparison is made between the link budget in THz frequencies and the expected attenuation for free space optics (FSO) links. Using the modified millimeter-wave propagation model, the frequency-dependent attenuation and group delay are expressed in terms of the complex refractivity of the atmospheric medium. The theory is employed to study the effect of fog and clouds on the accuracy of a frequency-modulated continuous-wave high-resolution radar operating at 330 GHz. In an experiment, the propagation of MMW was studied in a controlled fog chamber for various ranges of visibility, even below 1 m. The resulting attenuation and group delay of submillimeter waves were measured, while the properties of fog (optical visibility distance and water content) were monitored using FSO techniques. Apart from attenuation, the incremental group delay caused by fog also affected the accuracy of the radar. The experimental results were compared with those of an analytical model and were in good agreement even for very low visibility in very foggy conditions. Dispersive effects should be considered in the design of remote sensing radars operating in the MMW and THz regimes.

AMSUTRAN: A microwave transmittance code for satellite remote sensing

We present the microwave line-by-line model AMSUTRAN, which has been developed at the Met-Office (UK) for over 20 years as part of the EUMETSAT-funded Numerical Weather Prediction Satellite Application Facility (NWP SAF). It produces profiles of layer-to-space transmittances that are representative of the swath of a satellite channel, which are used to train coefficients for the fast radiative transfer model RTTOV (Radiative Transfer for TOVS). At its core are absorption routines based on the Millimeter-wave Propagation Model (MPM), with subsequent modifications to its structure and spectroscopy that have been implemented over time. The most significant of these are: adoption of the Curtis-Godson method of determining the most representative quantities for an atmospheric layer, the complete replacement of all oxygen line parameters, replacement of the air-broadened half-width parameters of the 22.235 and 183.31 GHz water vapour lines, the addition of 35 ozone lines from the HITRAN database, and modifications to the dry continua. The impact of each change is shown in terms of the change in Top Of Atmosphere (TOA) brightness temperature simulated for the 22 channels of the Advanced Technology Microwave Sounder (ATMS) satellite instrument. The biggest effect by far is seen in the method of determining layer quantities, with sensitivities up to many degrees kelvin. To date, developments have focused on the 0–200 GHz range as this is the spectral limit of the current microwave radiometers in-orbit, however, a new generation of instruments heralded by the forthcoming Ice Cloud Imager (ICI) planned for launch in 2022, raises the performance requirements of AMSUTRAN to sub-millimetre frequencies.

Boundary-layer water vapor profiling using differential absorption radar

Abstract. Remote sensing of water vapor in the presence of clouds and precipitation constitutes an important observational gap in the global observing system. We present ground-based measurements using a new radar instrument operating near the 183 GHz H2O line for profiling water vapor inside of planetary-boundary-layer clouds, and develop an error model and inversion algorithm for the profile retrieval. The measurement technique exploits the strong frequency dependence of the radar beam attenuation, or differential absorption, on the low-frequency flank of the water line in conjunction with the radar's ranging capability to acquire range-resolved humidity information. By comparing the measured differential absorption coefficient with a millimeter-wave propagation model, we retrieve humidity profiles with 200 m resolution and typical statistical uncertainty of 0.6 g m−3 out to around 2 km. This value for humidity uncertainty corresponds to measurements in the high-SNR (signal-to-noise ratio) limit, and is specific to the frequency band used. The measured spectral variation of the differential absorption coefficient shows good agreement with the model, supporting both the measurement method assumptions and the measurement error model. By performing the retrieval analysis on statistically independent data sets corresponding to the same observed scene, we demonstrate the reproducibility of the measurement. An important trade-off inherent to the measurement method between retrieved humidity precision and profile resolution is discussed.

Erratum to “Atmospheric Humidity Sounding Using Differential Absorption Radar Near 183 GHz” [Feb 18 163-167

In <xref ref-type="bibr" rid="ref1" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">[1, Fig. 5]</xref> , the assumed atmospheric conditions were incorrectly stated for the curve showing the millimeter-wave propagation model of excess attenuation at frequencies with respect to 193 GHz. Rather than being for 91% relative humidity (RH) and 289 K, as was stated in <xref ref-type="bibr" rid="ref1" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">[1]</xref> , the model curve in <xref ref-type="bibr" rid="ref1" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">[1, Fig. 5]</xref> was for 50% RH and 289 K. (The experimental measurements are unaffected.) The figure is reproduced here as <xref ref-type="fig" rid="fig1" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Fig. 1(a)</xref> , now with correct labeling.

Millimeter-wave propagation measurements and models at 28 GHz and 38 GHz in a dining room for 5G wireless networks

To meet 5G requirements, industries are looking forward to a new set of frequency allocation in the millimeter spectrum space, where there is huge amount of bandwidth for wireless gigabit communications. In this paper, the statistics of large-scale path loss and time dispersion parameters are investigated based on ultra-wideband measurements using a steerable directional horn antenna at transmitter (Tx) and omni-directional antenna at the receiver (Rx). The measurement was conducted in a dining room line-of-sight (LOS) scenario, which represents a typical closed-plan for in-building communication. The single-frequency, multi-frequency directional and omni-directional large-scale path loss models are evaluated at 28 GHz and 38 GHz bands based on data acquired from unique Tx and Rx antennas with combination pointing angles. The results show that the large-scale path loss models for indoor propagation developed in this paper is less complex, and yet more physically-based than those used in the third-generation partnership project (3GPP) systems, which involve additional model parameters but yield less accurate results. The time dispersion statistics for mmWave systems using directional antennas and omni-omni antennas configuration at both Tx and Rx are presented for co-polarization scenarios. We show that the multipath root mean square delay spread can be reduced when Tx and Rx antenna are pointed to each other, which results in the strongest received power.

Millimeter Wave High Resolution Radar Accuracy in Fog Conditions-Theory and Experimental Verification.

Attenuation and group delay effects on millimeter wave (MMW) propagation in clouds and fog are studied theoretically and verified experimentally using high resolution radar in an indoor space filled with artificial fog. In the theoretical analysis, the frequency-dependent attenuation and group delay were derived via the permittivity of the medium. The results are applied to modify the millimeter-wave propagation model (MPM) and employed to study the effect of fog and cloud on the accuracy of the Frequency-Modulated Continuous-Wave (FMCW) radar operating in millimeter wavelengths. Artificial fog was generated in the experimental study to demonstrate ultra-low visibility in a confined space. The resulted attenuation and group delay were measured using FMCW radar operating at 320–330 GHz. It was found that apart from the attenuation, the incremental group delay caused by the fog also played a role in the accuracy of the radar. The results were compared to the analytical model. It was shown that although the artificial fog has slight different characteristics compare to the natural fog and clouds, in particle composition, size, and density, the model predictions were good, pointing out that the dispersive effects should be considered in the design of remote sensing radars operating in millimeter and sub-millimeter wavelengths.

On the problem of high-accuracy modeling of the dry air absorption spectrum in the millimeter wavelength range

A detailed analysis of the dry air spectrum in the frequency range 180–260 GHz is given. The contributions of monomolecular and bimolecular absorption are discussed. It is shown that the effect of collisional coupling of zero-frequency transitions has a significant impact (up to 60%) on the value of nonresonance absorption. The coefficients of the empirical approximation of the "dry" continuum are redefined. A comparison with the continuum approximation from the Millimeter-wave Propagation Model is given.

Analysis of a Frequency-Hopping Millimeter-Wave Cellular Uplink

Fifth-generation (5G) cellular networks are expected to exhibit at least three primary physical-layer differences relative to fourth-generation ones: millimeter-wave propagation, massive antenna arrays, and densification of base stations. As in fourth-generation systems, such as LTE, 5G systems are likely to continue to use single-carrier frequency division multiple-access (SC-FDMA) on the uplink due to its advantageous peak-to-average power ratio. Moreover, 5G systems are likely to use frequency hopping on the uplink to help randomize interference and provide diversity against frequency-selective fading. In this paper, the implications of these and other physical-layer features on uplink performance are assessed using a novel millimeter-wave propagation model featuring distance-dependent parameters that characterize the path-loss, shadowing, and fading. The analysis proceeds by first fixing the location of the mobile devices and finding the performance conditioned on the topology. The spatially averaged performance is then found by averaging with respect to the location of the mobile devices. The analysis allows for the use of actual base-station topologies and the propagation model can leverage empirical millimeter-wave measurements. The benefits of base-station densification, highly directional sectorization, frequency hopping, a large available bandwidth, and a high code rate are illustrated. The minor importance of fractional power control is shown.

Analysis of Water Vapor Correction for CloudSat W-Band Radar

We analyzed different models to estimate absorption at W-band by gaseous species by taking advantage of the collocated CloudSat-Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation (CALIPSO) measurements. We used the power backscattered by the surface in the green visible wavelength of the lidar of CALIPSO as a reference to infer CloudSat's 94-GHz ocean surface backscatter in clear air and infer the attenuation introduced by gaseous absorption. Different millimeter-wave propagation models (MPMs) and different sources to determine the profile of atmospheric thermodynamic state are used to estimate CloudSat attenuation. These estimates are compared to the observations to calculate the residual dispersion. We show here that we need to adjust the empirical constants of preexisting water vapor absorption models to minimize the dispersion. Our results indicate an overestimation of absorption by the water vapor continuum at 94 GHz in Liebe-based MPM. We also propose a new empirical model to better represent the absorption of the water vapor continuum near 94 GHz. When this model is used in combination with the Advanced Microwave Scanning Radiometer for the Earth Observing System water vapor path and the Global Modeling and Assimilation Office water vapor vertical profile distribution, it leads to the lowest dispersion of the data on a statistical basis (global data over one month). The improved model is expected to optimize water vapor correction applied to CloudSat data and, potentially, also to improve interpretation of brightness temperature measurements in the W-band (e.g., 85- and 98-GHz radiometric channels).

Line mixing in the 60-GHz atmospheric oxygen band: Comparison of the MPM and ECS model

Precise profiles of the 60-GHz molecular oxygen band recorded earlier in a wide temperature range by means of a resonator spectrometer at atmospheric pressure were treated. High signal-to-noise ratio allows careful study of the band shape taking into consideration the mixing effect. Comparative analysis of the band profile calculated by an extended MPM (Millimeter-wave Propagation Model) and by the ECS (Energy Corrected Sudden) approximation model is presented. Some limitations of the MPM approach are discussed on the basis of the comparison of the two models. Interbranch coupling is shown to make a noticeable contribution to absorption which means that it should be taken into account as it is expected to improve band profile modeling accuracy.

In Memoriam: Hans Joachim Liebe

Hans Joachim Liebe, an internationally recognized expert in radiowave physics, and developer of the widely-used Millimeter-wave Propagation Model (MPM), passed away peacefully on August 2, 2012, after a long and courageous battle with Parkinson's disease. He was the son of Margarete and Fritz Liebe, and was born in Insterburg, East Prussia, Germany, on January 21, 1934. He married Roswita Borgwardt in 1963, and they were married 49 years. In 1964, he graduated magna cum laude from the Technical University of Berlin, where he earned the PhD in Electrical Engineering. In 1965, he moved from Germany to the United States with his family.

60-GHz oxygen band: Precise experimental profiles and extended absorption modeling in a wide temperature range

The 60-GHz band of atmospheric oxygen was studied in the temperature range of −28° to +60 °C at atmospheric pressure by means of a resonator spectrometer with absorption-variation sensitivity of 0.002 dB/km. The experimental data obtained have sufficient signal-to-noise ratio to take second-order mixing into account, increasing the accuracy of the millimeter-wave propagation model (MPM). A refined set of mixing coefficients for the model is derived from the new data and presented. The fidelity of the new model to the spectrometer data is generally better than 2% between 54 and 65 GHz.

Modeling of the absorption profile of the 60 GHz band of atmospheric oxygen using the memory function formalism

The profile of the oxygen absorption band centered at 60 GHz is modeled using the formalism of memory functions. The memory function determines the relation between the initial and final states of a molecule after its collision. The model profile takes into account the spectral exchange and contains two parameters, which depend on temperature and pressure. These parameters characterize the probabilities of spectral exchange between series of lines (branches) corresponding to molecular transitions of different types. To describe the absorption profile in the frequency range of 0–120 GHz in terms of the model proposed, the “+” and “−” branches of fine structure transitions and the series of nonresonance lines with frequencies on the order of 10−3–10−5 GHz are taken into account. The values of the parameters that take into account the spectral exchange are found from the condition of the best fit between the developed model profile and the profile calculated according to the millimeter-wave propagation model. The parameters found have physically substantiated and smooth temperature dependences, which confirms the adequacy of the model. The difference between these models does not exceed 2–3%, which corresponds to the declared uncertainty.

Reply to the comment on "Uncertainties in the temperature dependence of the line-coupling parameters of the microwave oxygen band: impact study"

For original paper see Boukabara et al., ibid., vol. 43, no.5, p.1109 (2005) and for comment see Rosenkranz., p.2160 (2005).The impact study described by Boukabar is, in essence, a theoretical sensitivity analysis of the temperature dependence of the line coupling coefficients in the microwave oxygen absorption band as accounted for in the millimeter-wave propagation model (MPM). The study was driven by emerging highly demanding requirements in terms of accuracy of the brightness temperatures measurements and therefore equally demanding requirements for models that simulate them. The main conclusions of the study are twofold: 1) the need to extend experimental measurements to the lower range of the atmospheric temperatures and 2) that errors due to uncertainties in the temperature dependence, are not necessarily entirely removable by a bias correction. The spectral region, where most of the impact was found, is located at the edge of the absorption band, especially in dry conditions. Rosenkranz commented on the work by Boukabara et al. and they now reply to these comments.

Comment on "Uncertainties in the temperature dependence of the line-coupling parameters of the microwave oxygen band: impact study"

For original paper see ibid., vol.43, no.5, p.1109-14 (2005). Boukabara et al. assert that uncertainties in oxygen line-coupling parameters in the Millimeter-wave Propagation Model (MPM92) may introduce errors of several degrees in brightness temperature at frequencies used by satellite radiometers. However, the methodology used by Boukabara et al. overestimates uncertainty in the model predictions, and it is shown that the simulations based on it are inconsistent with previously published atmospheric measurements.