Water Vapor Radiometer Research Articles

Consistency of the Troposphere Wet Delay From Water Vapor Radiometer and Co‐Located GPS Station

AbstractThe tropospheric delay acquired by the Global Navigation Position System (GPS) Precise Point Positioning (PPP) is continuous and steady, less affected by rainfall. The Water Vapor Radiometer (WVR) can provide real‐time meteorological parameters but is more sensitive to high‐frequency information in troposphere. To explore the use of WVR‐retrieved tropospheric delay and assist other geodetic techniques for atmospheric correction, the tropospheric delay from WVR and co‐located GPS at Shanghai, Beijing, Kunming, and Urumqi stations in China are compared. For the inconsistent values of WVR‐PPP zenith wet delay, the variations of the tropospheric delay from WVR and GPS before and after the rainfall were statistically analyzed. The results suggest that, for the rain rate ranging from 0.1 to 50 mm/hr, the impact of rainfall on WVR could last from 10 min before to 30 min after the rainfall. With filtering WVR data based on meteorological parameters and rain rate, the zenith wet delay between WVR and PPP at Shanghai shows good consistency, the root mean square (RMS) is 6.11 mm, correlation is 0.997, and the RMS in the other three stations ranges from 16.35 to 25.16 mm (correlation ranges in 0.794–0.951). The analysis indicates that the tropospheric delay of WVR is reliable to be applied to space geodetic techniques correction in real‐time with filtering to reduce the effect of rainfall, water vapor, and liquid water variability.

Measurements and Evaluations of the Atmospheric Transparency at Short Millimeter Wavelengths at Candidate Sites for Millimeter- and Sub-Millimeter-Wave Telescopes

Radio astronomical observations at millimeter and submillimeter wavelengths are a very important tool for astrophysical research. However, there is a huge area in northeastern Eurasia, including the whole Russian territory, which lacks sufficiently large radio telescopes effectively operating at these wavelengths. In this review, we describe our long-term efforts to find suitable sites for such radio telescopes in this area, that is, sites with good atmospheric transparency at millimeter and submillimeter waves. We describe methods and instruments used for measurements and evaluations of the atmospheric opacity. They include special radiometric systems, which are used for estimations of the atmospheric opacity in the transparency windows from the sky brightness measurements. Evaluation of the precipitable water vapor from such measurements by the artificial neural network is discussed. Other approaches use water vapor radiometers, global atmospheric models and signals of the Global Navigation Satellite Systems. To date, long-term radiometric monitoring has been performed at several candidate sites, and atmospheric conditions for many sites have been evaluated using global atmospheric models. Several sites with the best atmospheric transparency at millimeter and submillimeter wavelengths have been selected. They can be effectively used for astronomical observations, at least in the major atmospheric transparency windows at 1.3 mm and 0.85 mm. In general, the results show that northeastern Eurasia is a promising area for submillimeter astronomy. These results can also be used for space communications and radar systems.

Improvement of research methodology mesostructures of atmospheric fronts on the basis of ground­based microwave radiometry

The paper considers the some results of experimental studies of the mesoscale structure of atmospheric fronts using a ground-based microwave water vapor radiometer. A methodology for studying the mesoscale structure of atmospheric fronts is described, which includes two stages: the stage of syn- optic (frontological) analysis and the stage of mesoscale analysis based on measurements of atmospheric moisture and cloud liquid water content using a microwave water vapor radiometer. The application of the methodology is demonstrated by the example of the analysis of the results of observation of the case of the passage of warm and cold fronts through the Leningrad region on September 9—14, 2020. Based on the analysis of the results of previous studies, the features of changes in the characteristics of moisture content during the passage of atmospheric fronts are generalized. The growth of the atmospheric water vapor and cloud liquid water content is delayed relative to the appearance of harbingers of a warm cloud front of the upper tier. The growth of moisture content characteristics has a wave-like character, which can be explained by the manifestation of the strip mesostructure of the front. Estimates of the characteristic scales of spatial heterogeneities in the structure of atmospheric fronts for the area under consideration differ from similar characteristics obtained by P. Hobbs for the northeastern coast of North America. In the course of mesoscale analysis, the type of atmospheric front crossing the observation point can be clarified. The results obtained determine the prospects for improving the methods of diagnostics and current forecasting of dangerous weather phenomena during the passage of atmospheric fronts using ground-based microwave radiometers

Measurement of supercooled liquid water path in cold clouds based on a 183GHz airborne microwave radiometer

When flying through clouds that co ntain supercooled liquid water, aircraft can accumulate ice at levels that can be dangerous to flight. Similarly, in the field of weather modification, the amount and distribution of a cloud's supercooled water content is an important indicator of artificial precipitation. The G-band water Vapor Radiometer (GVR) is a small instrument that can be mounted on aircraft. Its operating frequency is highly sensitive to low liquid water content, which is particularly suitable for detecting supercooled water in different parts of clouds during changes in flight position. In order to explore supercooled water, we installed such an instrument with four double-sideband receiver channels centered at 183.31 ± 1, ±3, ±7, and ±14GHz, under the right wing of a King Air B-10KL that we used to perform a series of outfield observations and artificial precipitation missions. In this paper, we discuss the feasibility of detecting supercooled liquid water in the clouds over North China with a GVR. A Back Propagation (BP) neural network algorithm that takes into account flight details including aircraft altitude, climate background and geographic location variations was developed to retrieve supercooled liquid water path (SLWP). A numerical simulation test using the radiosonde data as test samples showed that the retrieval results correlate highly with the radiosonde data calculation results, and that the algorithm was applicable for different seasons and different geographical locations. The algorithm was then applied to the aircraft outfield observations of supercooled liquid water and the results were compared with hotwire, another cloud liquid water observation instrument installed on the aircraft. Results here showed agreement in terms of trend. The observation of SLWPs over clouds thought to be of 0-value shows that the root mean square error of retrieval results is as low as 0.2 g m−2. This paper demonstrates that it is feasible to measure supercooled water over North China with GVR using the retrieval algorithm used here, which obtained good results and is able to compensate for the lack of reliable supercooled water detection instruments on the aircraft.

Observation of the Solar Eclipse on June 10, 2021 on the Water Vapor Radiometer of the Institute of Applied Astronomy, Russian Academy of Sciences

The results of observations of the solar eclipse on June 10, 2021, which were carried out at the Svetloeobservatory (60.53° N, 29.78° E, Leningrad Province) for the first time using the water vapor radiometerand radio telescopes RT-13 and RT-32 together are presented. The eclipse curves obtained at the radiometeroperating frequencies of 20.7 and 31.4 GHz were compared with the change in the area of the open part of theSun and show good agreement (match to an accuracy of 2% during the cloudless period). Assuming a uniformdistribution of radio brightness across the solar disk, the brightness temperature was estimated to be 9060 ± 380and 8050 ± 300 K at these frequencies, respectively. It was concluded that even in the epoch of a deep minimumof solar activity, the brightness of the solar disk in the microwave range remains unchanged (independentof the cycle number)

Tracking ALMA System Temperature with Water Vapor Data at High Frequency

As the world-leading submillimeter telescope, the Atacama Large Millimeter/submillimeter Array observatory is now putting more focus on high-frequency observations at Band 7–10 (frequencies from 275 to 950 GHz). However, high-frequency observations often suffer from rapid variations in atmospheric opacity that directly affect the system temperature T sys. Current observations perform discrete atmospheric calibrations (Atm-cals) every few minutes, with typically 10–20 occurring per hour for high frequency observation and each taking 30–40 s. In order to obtain more accurate flux measurements and reduce the number of atmospheric calibrations (Atm-cals), a new method to monitor T sys continuously is proposed using existing data in the measurement set. In this work, we demonstrate the viability of using water vapor radiometer (WVR) data to track the T sys continuously. We find a tight linear correlation between T sys measured using the traditional method and T sys extrapolated based on WVR data with scatter of 0.5%–3%. Although the exact form of the linear relation varies among different data sets and spectral windows, we can use a small number of discrete T sys measurements to fit the linear relation and use this heuristic relationship to derive T sys every 10 s. Furthermore, we successfully reproduce the observed correlation using atmospheric transmission at microwave modeling and demonstrate the viability of a more general method to directly derive the T sys from the modeling. We apply the semi-continuous T sys from heuristic fitting on a few data sets from Band 7 to Band 10 and compare the flux measured using these methods. We find the discrete and continuous T sys methods give us consistent flux measurements with differences up to 5%. Furthermore, this method has significantly reduced the flux uncertainty due to T sys variability for one data set, which has large precipitable water vapor fluctuation, from 10% to 0.7%.

Observation of the Solar Eclipse on June 10, 2021 on the Water Vapor Radiometer of the Institute of Applied Astronomy, Russian Academy of Sciences

Observation of the Solar Eclipse on June 10, 2021 on the Water Vapor Radiometer of the Institute of Applied Astronomy, Russian Academy of Sciences

Prediction of Atmospheric Noise Temperature at the Deep Space Network With Machine Learning

AbstractKa‐band (32 GHz) communications links utilized by the National Aeronautics and Space Administration (NASA) flight missions for science downlink are susceptible to degradation due to weather. In this study, a customized real‐time forecast system has been developed to predict zenith atmospheric noise temperature (Tatm) at the Deep Space Network (DSN) tracking sites using machine learning (ML). A random forest model is trained with the Global Forecast System (GFS) forecast and analysis datasets in addition to the Tatm measurements derived from on‐site advanced water vapor radiometers (AWVR). The real‐time forecast uncertainty is quantified for different error regimes using the Self‐Organizing Map method. The results show that the root mean square error (RMSE) of the 24‐hr Tatm prediction at Goldstone, CA increases with the increase of Tatm. At 90% of the time, the forecasts have RMSE (bias) of less than 3.50 K (0.16 K) for fair‐weather conditions with Tatm < 16 K. In comparison to the current approach in designing Ka‐band communications links, application of weather forecasts can increase data return to the downlink for 80% of the time. A downlink gain of up to 2.43 dB (75% more data) can be realized at 10° elevation angle when Tatm = 8.32 K.

Estimation of the Tropospheric Moisture Content Derived from GPS Observations, Radio Sounding Data, and Measurements with a Water Vapor Radiometer

Estimation of the Tropospheric Moisture Content Derived from GPS Observations, Radio Sounding Data, and Measurements with a Water Vapor Radiometer

Characteristics and Quality Control of Precipitable Water Vapor Measured by G-band (183 GHz) Water Vapor Radiometer

Characteristics and Quality Control of Precipitable Water Vapor Measured by G-band (183 GHz) Water Vapor Radiometer

Multi-Year Variations in Atmospheric Water Vapor in the Baikal Natural Territory According to GPS Observations

The data of GPS measurements at the permanent observation points IRKM (Irkutsk, 52°13′ N, 104°19′ E, h = 509 m), ULAZ (Ulan-Ude, 51°48′ N, 107°37′ E, h = 517 m) and BADG (Badary, 51°46′ N, 102°14′ E, h = 848 m) located within the Baikal natural area (Eastern Siberia) are considered. A comparison was made of the time series of the tropospheric moisture content levels obtained at the IRKM site from GPS observations and radiosonde data, and at the BADG site from GPS observations and measurements with a water vapor radiometer (WVR) during 2020. The average deviation of the difference in total moisture content data during 2020 in the form of precipitable water according to GPS and WVR observations was about 0.12 mm, or about 1.1% relative to the average value, and the cross-correlation coefficient between the data is very high (K = 0.92). The use of GPS observations to obtain continuous data on the moisture content of the troposphere is substantiated. A series of processed data on the total moisture content based on GPS measurements using surface meteorological data for the period 1999–2020 for the IRKM and ULAZ sites and for the period 2006–2020 for the BADG site were obtained. Linear trends of total moisture content were determined for observation points: IRKM (−0.35 mm per decade, –2.7%), ULAZ (+0.47 mm per decade, +3.9%) and BADG (+1.41 mm per decade, 13.4%). Moreover, at the IRKM and ULAZ points, the surface temperature trends in the same period were positive and amounted to +0.4 K and +0.7 K per decade, respectively. The article confirms the trends identified in the work of Ross and Elliott for the territory of Eastern Siberia.

Monitoring the Water Vapor Content at High Spatio-Temporal Resolution Using a Network of Low-Cost Multi-GNSS Receivers

The Global Navigation Satellite System (GNSS) has the capacity for remote sensing of water vapor content in the atmosphere. Post-processing of GNSS data can provide Integrated Water Vapor (IWV) with accuracies comparable to measurements of traditional sensors, i.e. water vapor radiometers. While GNSS meteorology benefits from thousands of permanent GNSS stations operating worldwide the spatial resolution of GNSS-derived IWV is limited to tens of kilometers. Further densification of GNSS networks is achievable with low-cost GNSS receivers. We investigated the feasibility of low-cost multi-GNSS receivers for monitoring IWV. The post-processing and the real-time solution are validated against 1) the results from a geodetic-grade GNSS receiver, 2) co-located water vapor radiometer, and 3) numerical weather model (NWM). Despite the high variability of the IWV during the validation period, the standard deviation of IWV differences with respect to the water vapor radiometer was 1.0 kg/m <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> and 1.5 kg/m <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> in post-processing and real-time, respectively. The city-scale variability of water vapor content in the atmosphere was monitored by a network of 16 low-cost GNSS receivers deployed in the city of Wroclaw, Poland. During rapidly changing weather conditions the disagreement between the low-cost GNSS-derived IWV field and the NWM reached up to 5.4 kg/m <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> and inter-station IWV differences exceeded 5 kg/m <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> . It has been demonstrated that low-cost GNSS receivers are reliable tools for precise determination of IWV, also in real-time. This study is the first to measure the water vapor content with a spatial resolution of single kilometers and to present a significantly diversified city-scale IWV field.

Estimation of the moisture content of the troposphere derived from GPS observations, radiosonde data, and measurements with a water vapor radiometer

Estimation of the moisture content of the troposphere derived from GPS observations, radiosonde data, and measurements with a water vapor radiometer

Error Correction of Water Vapor Radiometers for VLBI Observations in Deep-Space Networks

In this paper, we present the design and implementation tests of a water vapor radiometer (WVR) suitable for very long baseline interferometry (VLBI) observation. We describe the calibration method with an analysis of the sources of measurement errors. The experimental results show that the long-term measurement accuracy of the brightness temperature of the water vapor radiometer can reach 0.2 K under arbitrary ambient conditions by absolute calibration, receiver gain error calibration, and antenna feeder system temperature noise error calibration. Furthermore, we present a method for measurements of the calibration error of the oblique path measurement. This results in an oblique path wet delay measurement accuracy of the water vapor radiometer reaching 20 mm (within one month).

Machine learning methods for Precipitable Water Vapor estimation by radiometric data in millimetre wavelength

This work deals with the first try to calculate the amount of Precipitable Water Vapor (PWV) in atmosphere by using machine learning and AI methods. We use the detector voltages series measured by radiometric system “MIAP-2” as the initial data for machine learning. The radiometer MIAP-2 works by “atmospheric dip method” in 2mm and 3mm atmospheric transparency windows. We also have PWV data series collected by Water Vapor Radiometer and GNSS receiver for data validation. The best convergence results were demonstrated by the independent component analysis (ICA) method with coefficient of determination R2= 0.53 and artificial neural network method (ANN) with R2= 0.8. These methods allow to reduce the systematic errors due to direct PWV calculation from raw radiometric data avoiding unnecessary steps opacity calculation.

Integrated High-Accuracy Correction Technology of Radio-Wave Refraction for Deep-Space (High-Orbit) Targets

The radio-wave refraction error caused by the troposphere and ionosphere badly affects accuracy in terms of the navigation, positioning, measurement, and control of a target; it is the main source of errors in high-accuracy measurement and control systems. The high-accuracy technology needed for radio-wave refraction error correction (mainly in the troposphere and ionosphere) has been the focus of research for a long time. At present, the correction methods used for radio-wave refraction errors have a low accuracy. For an S-band radio-wave signal, the accuracy of refraction error correction can generally only reach m-level (elevation angle of 15° and above), and thus has difficulty meeting the requirements of dm-level accuracy refraction error correction for deep-space and high-orbit targets. To improve the accuracy of radio-wave refraction error correction for deep-space and high-orbit targets, a novel correction method for tropospheric and ionospheric range error due to refraction is proposed in this study, on the basis of the measured data from a water vapor radiometer and dual-frequency Global Navigation Satellite System (GNSS). The comprehensive calibration test is conducted in combination with the Chinese Area Positioning System (CAPS) in Kunming. Results show that this method can effectively correct the range error due to refraction that is caused by the troposphere and ionosphere. For an S-band radio-wave signal, the accuracy of refraction error correction can reach dm-level accuracy (elevation angle of 15° and above), which is 50% higher than that achieved with traditional methods. This work provides an effective support system for major projects, such as lunar exploration and Mars exploration.

GPS Meteorology : Error in the estimation of precipitable water by ground based GPS system in some meso-scale thunderstorms - A case study

Remote sensing by ground based GPS receivers provide continuous and accurate measurement of precipitable water (PW) of an order of 1.5 mm comparable to radiosondes and water vapour radiometers. In the present work we have examined the amount of PW variation in three thunderstorms accompanied with rain shower that occurred over the GPS station. In all the three thunderstorms event heavy rain was reported. However on comparison of observed rainfall with GPS estimated precipitable water (hourly) in real time, it is observed that among the three, in one event the amount of precipitable water (PW) is much less (~20mm) for the same amount of rainfall. After analysing and taken into account various source of error, we suspect that in a mesoscale thunderstorms or squall lines associated with heavy rainfall, discrepancies arise because the wet mapping functions that used to map the wet delay at any angle to the zenith do not represent the localized atmospheric condition particularly for narrow towering thunder clouds and non-availability of GPS satellites in the zenith direction. On the other hand for the larger thunder cells the atmosphere is very nearly azimuthally symmetric with respect to GPS receiver, the error due to the wet mapping function is minimal.

The experience of remote temperature-water content sounding of atmosphere during drift of R/V “Akademik Tryoshnikov”

For the first time experience was gained with the operation of Russian equipment for water content and temperature remote sensing of the lower atmosphere in the Arctic. The comparison the results of measurements by radiometric systems with data of radiosoundings in wide range of meteorological conditions had been executed. It is shown that mean difference between integral atmospheric water content, measured by water vapor radiometer WVR, and calculated from radiosoundings data does not exceed 6 % with standard deviation 0.54 kg/m2 and significant correlation coefficient 0,92. Analysis the data of meteorological temperature profiler MTR-5 allows to conclude that in general its adequately reproduce air temperature profiles in the atmospheric lower 1000 m layer. Some deviations take place only in cases of large temperature gradients. Preliminary analysis of WVR data showed that monthly mean value of integral atmospheric water content in area under study in April 2019 year practically coincides with calculated from radiosoundings, performed in 1983—1988 years at the polar station Barentsburg, nearest to the drift region, 3.61 and 3.62 kg/m2 respectively. Same time hourly mean values of integral atmospheric water content during drift varied from 2 to 10 kg/m2, with extreme values recorded between April 15 and April 20, probably due to intensive transport of air masses of the Atlantic origin. Based on MTR-5 data it was concluded that despite differences in sounding technology, the place and time of observations, the statistics of inversions registered during drift correspond well to statistics of inversions, recorded on the Arctic coastal stations and over sea ice cover of the Weddell Sea in winter.

Ground-based Microwave Radiometry for measurements of Atmospheric Water Vapour and Cloud Liquid Water Contents

The method of ground-based microwave radiometry for determining the integral parameters of atmospheric moisture content, such as integrated water vapor and cloud liquid water content is considered. Some results of experimental studies of integrated water vapor and integrated cloud liquid in different regions by means of ground-based and ship-based of microwave radiometers are given. The microwave radiometric measurements of integrated water vapor were found to be in agreement with independent radiosonding data (rms is ∼1 kg/m2). Microwave radiometric measurements of integrated cloud liquid of stratified clouds are consistent with empirical models of cloudy atmosphere based on aircraft data sensing of clouds. The capabilities of the novel microwave water vapor radiometer for studying variations in atmospheric moisture content on micro and meso scales were demonstrated. Histograms of the moisture content are obtained, and an approximation for the temporal structural function of the integrated water vapor in a wide range of time scales is discussed.

Comparing atmospheric data and models at station Wettzell during CONT17

Abstract. During the Continuous Very Long Baseline Interferometry (VLBI) Campaign 2017 (CONT17), carried out from 28 November through 12 December 2017, an extensive data set of atmospheric observations was acquired at the Geodetic Observatory Wettzell. In addition to in situ measurements of temperature, humidity, pressure or wind speed at the surface, radiosonde ascents yielded meteorological parameters continually up to 25 km height, and integrated water vapor (IWV) was obtained at several elevations and azimuths from a water vapor radiometer. Troposphere delays estimated from Global Navigation Satellite Systems (GNSS) observations plus comparative values from two different Numerical Weather Models (NWMs) complete the abundance of data. In this presentation, we compare these data sets to parameters of the Vienna Mapping Functions 1 and 3 (VMF1 &amp;amp; VMF3), which are based on NWM data by the ECMWF, and to estimates of VLBI analysis using the Vienna VLBI and Satellite Software (VieVS). On the one hand, we contrast the variety of troposphere delays in zenith direction with each other, while on the other hand we utilize radiosonde data and meteorological observations at the site to create local mapping functions which can then be compared to VMF3 and VMF1 at Wettzell. In general, we thus received very good accordance between the different solutions. Also in terms of the mapping functions, the local radiosonde mapping function is in consistence with VMF1 and VMF3 with differences less than 5 mm at 5∘ elevation.