1,720,973 research outputs found
Mapping the atmospheric water vapor by integrating microwave radiometer and GPS measurements
No full textThis paper deals with a procedure to generate maps of the integrated precipitable water vapor (IPWV) over the Mediterranean area by using estimates from a global positioning system (GPS) network over land and from the Special Sensor Microwave/Imager (SSM/I) over sea. In particular, we investigate the application of the Kriging geostatistical technique to obtain regularly spaced IPWV values. The horizontal spatial structure of water vapor retrieved by SSM/I is explored by computing variograms that provide a measure of dissimilarity between pairs of IPWV values for the region of interest. Because the water vapor density decreases with height, the GPS station elevation is accounted for in the interpolation procedure. In this respect, the potential of the Kriging with external drift relative to the ordinary Kriging is evaluated by applying a test based on the cross-validation approach. Case studies are presented and qualitatively compared to the corresponding Meteosat infrared images. A quantitative comparison with an independent source of information, such as IPWV computed from radiosonde observations and from European Centre for Medium-Range Weather Forecasts analysis, is also performed.
A tomographic approach to the retrieval of the atmospheric specific attenuation coefficient from measured brightness temperature
No full textThe authors propose an inversion scheme devoted to the retrieval of the atmospheric specific absorption coefficient based on data collected by a ground-based microwave radiometer. The technique processes elevation scans. The vertical plan is modelled by allocating M bins in the vertical directions. The forward modelling is defined by linearization of the radiative transfer equation around a reference model of the atmospheric parameter pattern. The goal is to estimate the atmospheric attenuation along the vertical path 3 km away from the radiometer location, where a transponder calibration device for the nadir looking RA-2 altimeter on board of the ENVISAT satellite is positioned. Estimation is performed through inversion of the brightness temperature values observed at different elevation angles, provided a proper parameterization of the model space. According to the agreement of the reference model to the actual conditions two cases are given: either the solution is acceptable or it is not reliable and a different inversion scheme is to be implemented. © 2012 IEEE
On the Use of Microwave Radiometers for Deep Space Mission Applications by Means of a Radiometric-Based Scalar Indicator
Full text linkThe estimation of the path delay due to water vapor is a crucial aspect for the calibration of the Doppler observables of a deep space probe. The advanced water vapor radiometer (AWVR) developed by the Jet Propulsion Laboratory (JPL, NASA) already proved its capability to accurately estimate the path delay during the entire Cassini mission. Here, from the AWVR measurements, a scalar sky status indicator (SSI) was developed as a criterion for selecting the radiometric path delay estimations in the orbit determination process. Results indicate that the use of such index allows a reduction of the range rate residual root mean square (rms)
Retrieval of sun brightness temperature and precipitating cloud extinction using ground-based sun-tracking microwave radiometry
No full textSun-tracking (ST) microwave radiometry is a technique where the Sun is used as a microwave signal source and it is here rigorously summarized. The antenna noise temperature of a ground-based microwave radiometer is measured by alternately pointing toward-the-Sun and off-the-Sun while tracking it along its diurnal ecliptic. During clear sky the brightness temperature of the Sun disk emission at K and Ka band and in the unexplored millimeter-wave frequency region at V and W band can be estimated by adopting different techniques. Using a unique dataset collected during 2015 through a ST multifrequency radiometer, the Sun brightness temperature shows a decreasing behavior with frequency with values from about 9000 K at K band down to about 6600 K at W band. In the presence of precipitating clouds the ST technique can also provide an accurate estimate of the atmospheric extinction up to about 32 dB at W band with the current radiometric system. Parametric prediction models for retrieving all-weather atmospheric extinction from ground-based microwave radiometers are then tested and their accuracy evaluated
Sun-tracking microwave radiometry: all-weather estimation of atmospheric path attenuation at Ka, V and W band
No full textSun-tracking (ST) microwave radiometry is a ground-based technique where the Sun is used as a beacon source. The atmospheric antenna noise temperature is measured by alternately pointing toward-the-Sun and off-the-Sun according to a beam switching strategy. By properly developing an ad hoc processing algorithm, we can estimate the atmospheric path attenuation in all-weather conditions. A theoretical framework is proposed to describe the ST radiometric measurements and to evaluate the overall error budget. Two different techniques, based, respectively, on elevation-scanning Langley method and on surface meteorological data method, are proposed and compared to estimate the clear-air reference. Application to available ST radiometric measurements at Ka-, V-, and W-band in Rome (NY, USA) is shown and discussed together with the test of new physically based prediction models for all-weather path attenuation estimation up to about 30 dB at V- and W-band from multichannel microwave radiometric data. Results show an appealing potential of this overall approach in order to overcome the difficulties to perform satellite-to-earth radiopropagation experiments in the unexplored millimeterwave and submillimeter-wave frequency region, especially where experimental data from beacon receivers are not available
Modeling and Predicting Sky-Noise Temperature of Clear, Cloudy, and Rainy Atmosphere From X- to W-Band
No full textA physically-based parametric model (PPM) to predict the sky-noise temperature in all weather conditions is proposed. The proposed prediction model is based on the non-linear regression fit of numerical simulations derived from the sky-noise eddington radiative-transfer model (SNEM) in an absorbing and scattering medium such as gaseous, cloudy and rainy atmosphere. The PPM prediction method, dependent on measured path attenuation, beacon frequency, and antenna-pointing elevation angle, describes the statistical behavior of the atmospheric mean radiative temperature, which in its turn relates sky-noise temperature to slant-path attenuation. PPM validity ranges from X- to W- band and from 10 degrees to 90 degrees in terms of elevation angle. A comparison of the estimated PPM radio-propagation variables with corresponding ITALSAT satellite data, collected at the Spino d'Adda receiving station (Italy), is also carried out and discussed. The PPM prediction technique provides a root-mean-square retrieval error generally less than 8 K for all frequencies. Results show an improvement with respect to the current International Telecommunication Union (ITU) recommendations, especially at Q- and V-band and above, where the atmospheric multiple scattering effects cannot be disregarded
Use of remote sensing techniques and navigation data for tropospheric channel assessment
No full textThe objective of this contribution is the review of remote sensing and navigation data in order to provide an overview on meteorological parameters important for propagation modelling up to W band. Such data are also useful to assess the accuracy of the propagation models and analyse propagation impairment mitigation techniques (PIMTs). The review will focus on water vapour and cloud properties that can be deduced from observation in various parts of the electromagnetic spectrum. Both ground measurements and satellite observations are considered which offer various possibilities to capture the spatial distribution of these parameters. For clouds the importance of microphysical properties, e.g., liquid water path and effective radius, is highlighted as they control the signal transfer. Several example of ongoing satellite missions are given. © 2011 EurAAP
Retrieval of precipitation extinction using ground-based sun-tracking millimeter-wave radiometry
No full textSun-tracking millimeter-wave radiometry exploits the Sun as a beacon source by tracking it along its diurnal ecliptic. The atmospheric brightness temperature is measured by alternately pointing toward-the-Sun and off-the-Sun according to ad hoc switching strategy. By properly developing a retrieval algorithm, we can estimate the atmospheric path attenuation in all-weather conditions. The Langley method, based on elevation-scanning, is proposed to estimate the equivalent brightness temperature of the Sun, which is a critical step for precipitation extinction estimation. An application to available Sun-tracking radiometric measurements at V and W band in Rome (NY, USA) is shown, discussed and compared with the conventional technique using the clear-air approximation of the mean radiative temperature. Results show an appealing potential of Sun-tracking technique in order to exploit millimeter-wave radiometry for atmospheric retrievals even in a cloudy and rainy conditions
On the accuracy of integrated water vapor observations and the potential for mitigating electromagnetic path delay error in InSAR
No full textA field campaign was carried out in the framework of the Mitigation of Electromagnetic Transmission errors induced by Atmospheric Water Vapour Effects (METAWAVE) project sponsored by the European Space Agency (ESA) to investigate the accuracy of currently available sources of atmospheric columnar integrated water vapor measurements. The METAWAVE campaign took place in Rome, Italy, for the 2-week period from 19 September to 4 October 2008. The collected dataset includes observations from ground-based microwave radiometers and Global Positioning System (GPS) receivers, from meteorological numerical model analysis and predictions, from balloon-borne in-situ radiosoundings, as well as from spaceborne infrared radiometers. These different sources of integrated water vapor (IWV) observations have been analyzed and compared to quantify the accuracy and investigate the potential for mitigating IWV-related electromagnetic path delay errors in Interferometric Synthetic Aperture Radar (InSAR) imaging. The results, which include a triple collocation analysis accounting for errors inherently present in every IWV measurements, are valid not only to InSAR but also to any other application involving water vapor sensing. The present analysis concludes that the requirements for mitigating the effects of turbulent water vapor component into InSAR are significantly higher than the accuracy of the instruments analyzed here. Nonetheless, information on the IWV vertical stratification from satellite observations, numerical models, and GPS receivers may provide valuable aid to suppress the long spatial wavelength (>20 km) component of the atmospheric delay, and thus significantly improve the performances of InSAR phase unwrapping techniques
Satellite-based retrieval of precipitable water vapor over land by using a neural network approach
No full textA method based on neural networks is proposed to retrieve integrated precipitable water vapor (IPWV) over land from brightness temperatures measured by the Advanced Microwave Scanning Radiometer-Earth Observing System (AMSR-E). Water vapor values provided by European Centre for Medium-Range Weather Forecasts (ECMWF) were used to train the network. The performance of the network was demonstrated by using a separate data set of AMSR-E observations and the corresponding IPWV values from ECMWF. Our study was optimized over two areas in Northern and Central Italy. Good agreements on the order of 0.24 cm and 0.33 cm rms, respectively, were found between neural network retrievals and ECMWF IPWV data during clear-sky conditions. In the presence of clouds, an rms of the order of 0.38 cm was found for both areas. In addition, results were compared with the IPWV values obtained from in situ instruments, a ground-based radiometer, and a global positioning system (GPS) receiver located in Rome, and a local network of GPS receivers in Como. An rms agreement of 0.34 cm was found between the ground-based radiometer and the neural network retrievals, and of 0.35 cm and 0.40 cm with the GPS located in Rome and Como, respectively
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