The NDSA technique, proposed for estimating the IWV (Integrated Water Vapor) through a tropospheric radio link, operates by transmitting two sinusoidal signals at K band and gauging their reception power. This enables the estimation of IWV based on the different signals’attenuation. In 2018, an instrument prototype was finalized for the first measurement campaign, showcasing the NDSA method. In this paper we describe the improved version of the instrument, used for a second campaign in 2022, the procedures for its characterization and generation of data, and some of the campaign outcomes.

Accurate quantitative precipitation estimation (QPE) methods are essential for weather forecasting and for prevention of hydrogeological risk. QPE becomes even more important when facing severe precipitation events. In this letter, a comparison among different rainfall estimation methods is presented, using a severe event that occurred in Italy as a case study. In particular, the focus is on a merging method based on the dynamic adaptation of the Z–R relationship according to the spatiotemporal evolution of the observed phenomenon. Through a cross-validation analysis, we quantitatively assess the effectiveness of such a method: compared with the others, it performs better on the average, while it can outperform them in critical rainfall conditions, confirming its potential for localizing and monitoring areas with greatest risks.

The Normalized Differential Spectral Attenuation technique (NDSA) has been proposed as a method for measuring Integrated Water Vapor (IWV) by means of attenuation measurements in the Ku-/K-band along tropospheric microwave links. After a first measurement campaign aimed at demonstrating the NDSA method, a second field experiment has been carried out from August 1 to November 30, 2022. The transmitter was placed on the top of Monte Gomito (44.1277° lat, 10.6434° lon, 1892 meters a.s.l.) and the receiver on the roof of the Department of Information Engineering of the University of Florence (43.7985° lat, 11.2528° lon, 50 meters a.s.l.). The resulting radio link length was 61.15 km. Four ground weather stations of the regional weather service were selected among those available. The purpose is comparing the IWV estimates provided by NDSA measurements with the ground point data of air temperature, air humidity, barometric pressure, and rainfall.

In this paper, we address the problem of combating the effect of the nonlinearities of the transmit-receive chain in solid-state radars, which are typically generated by the power amplifier in transmission. This issue is of particular importance in meteorological radar applications, as they require transmit pulses featuring very low autocorrelation sidelobes, which are significantly raised due to nonlinearities. In this work, we describe an adaptive predistortion design method based on an iterative approach in the spectral domain. The proposed method has been validated by means of hardware using a customized software radio and driving an amplifier into saturation. Two different ideal, highly performing pulse compression waveforms, expressly designed for weather radar applications, were sent to its input. The experimental results demonstrate the benefits of the proposed approach to design the digital predistortion module.

Measurement of water vapor (WV) in the lower troposphere on a continuous temporal basis would improve our knowledge of the atmospheric dynamics and the performance of numerical weather prediction models. In recent studies, a new measurement concept, the normalized differential spectral attenuation (NDSA) approach, was proposed. It is based on measurements of differential attenuation at 18.8 and 19.2 GHz performed along a tropospheric radio link. While NDSA measurement at a fixed elevation angle provides information on integrated WV (IWV), measurements at different elevation angles allow to retrieve the vertical WV content profile. A prototype NDSA demonstrator, which consists of two units, a synthesized transmitter and a software-defined radio receiver, has been designed and implemented. The system was accurately characterized through several laboratory tests, and then a first experimental campaign was conducted at fixed elevation angle along a ground-to-ground radio link. Obtained results confirm the sensitivity of the NDSA measurements to the IWV along such link with a good agreement with the existing ground-based and satellite data products.

This paper illustrates the first results of the analysis carried out to check the possibility to provide an estimate of the Integrated Liquid Water (ILW) content along a microwave link established between the multifrequency transmitter and the receiver on board a couple of Low Earth Orbiting (LEO) satellites. The ILW estimate is provided through the power ratio of the received signals at 32 and 17 GHz. The results have been obtained using a simulation tool developed for LEO satellites orbiting in the same plane and along the same angular direction (co-rotating satellites), assuming some high-resolution atmospheric scenarios generated by using the WRF (Weather Research and Forecasting) numerical weather prediction model.

Recently, inversion of Integral Water Vapor (IWV) measurements, obtained through the use of the Normalized Differential Spectral Absorption (NDSA) has been proposed to retrieve the tropospheric Water Vapor (WV) content. In this paper, the results of the application of the External Reconstruction Tomographic Algorithm (ERTA) to that problem are presented. The results have been obtained by considering a measurement scenario composed of LEO satellites orbiting in the same plane and along the same angular direction (co-rotating satellites).

Accurate measurement and monitoring of precipitation is crucial for many applications, such as flood and drought risk assessment and management. Conventional meteorological devices for estimating precipitation (i.e., rain gauges, disdrometers, active and passive remote sensors, be they ground-based, spaceborne, or airborne) have their own strengths and weaknesses. The latter are often related to time and space resolution, coverage, and cost. In the last two decades, several studies have been carried out to exploit opportunistic signals of terrestrial microwave communication links to improve precipitation estimation capability. This study describes and evaluates a method to retrieve rainfall rate from the signal-to-noise ratio obtained from commercial interactive digital video broadcasting (DVB) receivers [referred as to smart low-noise blocks (smartLNBs)]. During a 1-year measurement campaign carried out in Tuscany (Italy) with purposely deployed instruments, the precipitation values estimated from a set of SmartLNBs were compared with measurements from co-located rain gauges and disdrometer. The normalized mean absolute error (NMAE) and root-mean-square error (RMSE) obtained comparing the total cumulative precipitation from a SmartLNB and a disdrometer are 48.8% and 7.46 mm, respectively. Encouraging results also come from comparing the total precipitation amounts as measured by the SmartLNBs and by the rain gauges, with values of NMAE (respectively, RMSE) ranging between 44% and 82% (respectively, 5.2 and 11.5 mm).

This article addresses the problem of radar pulse compression. First, a matched filter at the receiver is assumed and a method to design a transmit waveform characterized by an autocorrelation function with a narrow mainlobe and low sidelobes is proposed. After that, a mismatched filter is considered and a method to design the optimum linear filter receiver is proposed. In both cases, the pursued objectives are minimum sidelobe energy and peak level through a strategy based on quadratic and nonlinear optimization. In this article, we focus particularly on the case of ground weather radars, where the problem of pulse compression is particularly challenging.

In recent years, severe weather phenomena have occurred with increasing frequency throughout the Mediterranean area. Because of the extreme intensity of the phenomena and of their small spatio-temporal scales, an early warning of severe rainfall through a timely and accurate estimation is crucial for reducing the hydrological risk and for disaster mitigation. On the other hand, the rain-gauge networks are often not able to detect rainfall due to their limited sampling capability, as occurred in the two case studies presented in this work, characterized by severe weather conditions. For both case studies, we utilized a data-fusion procedure aimed at real-time estimation of cumulative rainfall fields, based on the reflectivity factor Z provided by ground weather radar and rain-gauge estimates of the rainfall intensity R. The use of Z-R relationships determined a priori, as typically done by operational weather services, is not appropriate for obtaining accurate rainfall estimates, as needed, for instance, to forecast flash flood events. Consequently, additional information is needed. The procedure utilized is based on an adaptive data-fusion technique, relying on the dynamic adjustment of the coefficients of the Z-R relationship to the observed phenomenon. Its application to two severe weather case studies demonstrated the capability of the methodology to correctly identify and monitor areas of high potential risk as well as to provide rainfall estimates in such areas.

A simulator of weather radar signals can be exploited as a useful reference for many applications, such as weather forecasting and nowcasting models or for training artificial intelligence systems designed to optimize the trajectory of aircrafts with the purpose to reduce flight hazard and fuel consumption. However, before being used, it must be accurately examined under different operating conditions, in order to evaluate the consistency of the outputs produced. In this paper, we present a validation procedure for a newly developed polarimetric weather radar simulator (POWERS). The goal is to assess the ability of the simulator to deal with any kind of input data, be they simulated and real raindrop-size distributions, or outputs generated by numerical weather prediction models. Three different approaches are proposed, each providing a connection between meteorological inputs and the radar observables simulated by POWERS. The analysis is carried out in the case of rainfall, both at S- and X-bands.

The knowledge of the water vapor (WV) distribution in the Earth's atmosphere is of great importance for weather prediction. Meteorological models, in particular, the so-called limited area models, can assimilate humidity measurements, increasing the reliability of the simulated atmospheric dynamics. An important improvement can be achieved, for instance, if we are able to provide the total column with a sufficient precision and accuracy. In this paper, the novel normalized differential spectral attenuation (NDSA) approach is applied to retrieve the vertical profile of WV-and thus the total column-from measurements of differential attenuation signals at microwaves. A forward model (FM) has been used to simulate the ray-tracing of a microwave signal from a transmitter to a receiver in the atmosphere by using the 3-D atmospheric parameters as provided by a numerical weather prediction (NWP) model. From the NDSA measurement, the integrated WV (IWV) content can be directly derived. A further retrieval code is able to invert the measurements of IWV along the path length, providing the vertical humidity profile, which is directly related to the total vertical column assimilated by weather prediction models. In this paper, we show that the values of the total column can be retrieved with a precision and accuracy up to about 0.6% and 2.1%, respectively, which could have a positive impact on NWP models at short time scale.

In this paper the methodology to retrieve the vertical profiles of water vapor starting from microwave measurements is discussed. The novel technique, is based on a microwave radio link and the measure of differential attenuation of two signals transmitted at closely spaced frequencies in the Ku-K band. The capability to gain insight about the water vapour distribution in atmosphere and the potential strong impact on the weather prediction chains is also discussed.

The measure of water vapor (WV) in the lowest part of the troposphere is a critical issue which, up to now, cannot be measured from space with sufficient accuracy. A novel technique, which is based on a microwave radio link and the measure of differential attenuation of two signals transmitted at closely spaced frequencies in the Ku-K band, has been recently proposed. In order to prove the potential of this technique a new low-cost microwave link has been designed and the first measurements will be performed by means of a ground-to-ground link. Instrument design and characteristics, as well as expected results are presented here.

The normalized differential spectral attenuation (NDSA) approach was proposed years ago as an effective way to estimate the integrated water vapor (IWV) along a tropospheric propagation path between two low Earth orbit satellites. Two applications are possible: the retrieval of vertical profiles of WV if the sense of rotation is opposite and the retrieval of 2D fields of WV over vertical tropospheric sections if the sense is the same. The method relies on the measurement of the so-called spectral sensitivity S at given frequencies, and on IWV-S relationships that convert S into an estimate of IWV along the radio link where S is measured. In this paper, we recompute the IWV-S relationships using synthetic atmospheres generated by means of European Centre for Medium-Range Weather Forecasts (ECMWF) analysis data instead of radiosonde profiles as done by ourselves in the past. Thanks to the uniform spatial distribution of the ECMWF data on a global Earth scale, we were able to validate the IWV-S relationships in the Ku/K band previously found through synthetic atmospheres generated by means of the aforementioned irregularly spaced radiosonde data, and to define the IWV-S relationships at 179 and 181 GHz that are exploitable in the upper troposphere. Since the ECMWF data also include information about the liquid water (LW) content, we then show that an additional S channel at 32 GHz can be exploited to detect and correct the bias induced by LW on IWV estimates made by applying the NDSA in the Ku/K band.

The use of the normalized differential spectral attenuation (NDSA) approach in the microwaves and (later) in the millimeter waves has been recently introduced to retrieve information about integrated water vapor (IWV) content from attenuation measurements along microwave links between two low Earth orbit (LEO) satellites. NDSA was originally proposed for a configuration of two counter-rotating satellites, to achieve vertical profiles of water vapor (WV) from IWV measurements. In this paper, we analyze the exploitability of the NDSA approach in the case of a constellation of corotating LEO satellites in order to estimate the WV content in a 2-D field lying in the orbital plane of the satellites. The WV retrieval is formalized as the solution of an inverse problem. Simulation results are presented in order to demonstrate the feasibility of the proposed approach: a complete acquisition system composed of transmitting and receiving LEO satellites, including tropospheric scintillation effects, has been modeled, and the reconstruction of 2-D maps of the atmospheric WV from multiple IWV measurements is shown.

This paper presents and discusses some results of a specific Weather Radar Post-Processor software that provides weather classification maps and related binary risk maps after the processing of dual polarization airborne X band radar outputs. Weather classification maps and binary risk maps are used as input to decision support systems for aircraft pilots in case of bad weather conditions. The software runs inside an Electronic Flight Bag and the results shown here are obtained using true flight plans coming from the flight management system of an ATR72 flight simulator. Dual polarization avionic X band radar outputs are generated assuming true weather scenarios with a radar signal simulation software developed by the research team of the Radar and Surveillance Systems Laboratory of CNIT.

This paper introduces additional results to those concerning the quasi-real-time estimation of rain rate through an opportunistic Ka-band satellite link, which has been recently presented. The focus of the present work is on the dependence of the proposed method from some model's parameters such as the clouds base height and the integration time for the received signal. The upgrade of the model is presented and its employment with a new set of collected data is presented. The results are interpreted through a comparison with measurements from a small network of rain gauges.

Polarimetric techniques applied to radars on-board civil aircraft can improve the estimation of risk zones due to dangerous weather during flight. Usually, X-band weather radars are installed at the nose of civil aircrafts. This band is affected by strong attenuation in case of intense precipitation (liquid or mixed phase). The current systems do not compensate backscattered power measurements for attenuation caused by propagation through precipitation, while dual-polarization radars are able to compensate effectively this source of error and to discriminate hydrometeors. In this work, a classification algorithm based on support vector machines (SVM) is proposed. Training is driven by the output of a Fuzzy Logic (FL) classification algorithm (typical classification approach used for ground-based weather radar). SVM high performance in terms of time processing and its flexibility of configuration using all type of inputs variables are important characteristics to be included in some avionic specific equipment, such as the Electronic Flight Bag (EFB). Two datasets have been used to test the SVM classification algorithm. The first dataset is composed of simulated radar polarimetric observations at X-band and the second one is composed of actual dual-polarization radar measurements collected during the Special Observation Period (SOP) 1.1 of HYdrological cycle in MEditerranean EXperiment (Hymex) campaign by the C-band Doppler dual-polarization weather radar (Polar 55C) installed at ISAC-CNR in Rome. Good performance are obtained for SVM classificator. The comparison with FL output shows a good agreement (up to 90%) both in qualitative comparison maps by maps and using a quantitative approach which metric is based on the confusion matrix.

This paper presents a study for the estimation of 2-D maps of atmospheric water vapour content from integrated water vapour measurements carried out by a constellation of co-rotating low earth orbit satellites. The proposed method uses the normalised differential spectral attenuation (NDSA) approach - able to achieve integrated water vapour content information from attenuation measurements over microwave links among the satellites - and tomographic techniques to solve the inverse problem of atmospheric water vapour field reconstruction. Simulation results demonstrate the feasibility of the proposed approach to retrieve a 2-D map of the atmospheric water vapour content. This study has been developed under the framework of the ANISAP project funded by the European Space Agency.

The normalised differential spectral attenuation (NDSA) approach has been recently introduced to retrieve integrated water vapour (IWV) content information from attenuation measurements over microwave links between two low earth orbit (LEO) satellites. In the original formulation, two counter-rotating satellites were considered in order to achieve vertical profiles of water vapour. In this paper, an extension of the method to the case of a constellation of co-rotating LEO satellites is proposed. Simulation results demonstrate the feasibility of the proposed approach to retrieve 2-D maps of the atmospheric water vapour content from IWV measurements.

In this work we present and discuss the effects of different scintillation models on the Normalize Differential Spectral Attenuation (NDSA) measurements in a counter-rotating Low Earth Orbiting (LEO) set event at 17, 19, 21, 32, 179 and 182 GHz. Some parameters of the scintillation models used here are computed at global scale using an European Centre for Medium-Range Weather Forecasts (ECMWF) global dataset. The scintillation effects on the NDSA measurements are analyzed in terms of relative error of the their estimation.

The 4-satellite constellation Cosmo Sky Med of the Italian Space Agency is providing high quality observations suitable for many applications in “all weather” conditions. However, Cosmo Sky Med SARs use a frequency at X-band (9.6 GHz) for which attenuation due propagation through precipitation is not negligible and can affect several SAR applications. In some conditions, especially heavy thunderstorms, precipitation effects can be significant, masking features of interest of the observed surface. During the two years of operation of Cosmo Sky Med, several images collected in stripmap, pingpong and scansar mode, both over sea and terrain and sea are analyzed and discussed by using simultaneous measurements collected by operational and research weather radar.

In this paper the main objectives of the ESA-ANISAP study are summarized and the first results are presented. The existing end-to-end software simulation tool developed for a couple of counter-rotating Low Earth Orbiting (LEO) satellites has been upgraded and utilized for this work. The Integrated Water Vapor (IWV) - Spectral Sensitivity (SS) and the Integrated Liquid Water (ILW) - SS relationships are shown assuming the acquisition of IWV and ILW at 3,6, and 9 km tangent altitude jointly with that of SS at 17, 19, 21 and 32 GHz. Such relationships are obtained for a global set of atmospheric vertical profiles, in order to compute the regression coefficients of the IWV-SS and ILW-SS relationships based on a linear least squares fit.

A software tool for the simulation of the received echo of an over the horizon sky wave radar in pulse mode has been developed. The tool accounts for several models of the pulse radar Tx/Rx configuration, the antenna pattern, the electron ionospheric structure and the land/sea backscattering of the Earth's surface. Some simulation products are presented and discussed assuming the Mediterranean Sea scenario.

A measurement approach is presented for estimating the gas emission flux by a surface source based on the use of infrared laser measurements along optical links. An ad hoc arrangement optical links surrounding the emission area allows one to measure gas concentration over a close surface corresponding to an air volume that covers the whole emission area. We show some simulation results of surface flux measurements assuming that the concentration measurements are made over five faces of a parallelepiped, while the sixth (bottom) face is the emission surface. We discuss some estimation results based on a stationary diffusion model applied to point sources where the air diffusion and transportation phenomena are due mainly to the horizontal wind.

NDSA (Normalized Differential Spectral Absorption) was proposed as a differential attenuation measurement method to estimate the total content of water vapor (IWV, Integrated Water Vapor) along a tropospheric propagation path between two Low Earth Orbit (LEO) satellites during a relative occultation event. The NDSA approach is based on the estimate of a “spectral sensitivity parameter” that can be directly converted into IWV through empirical relationships In this paper we present the multi-band approach to convert the five simultaneous Ku, K and M spectral sensitivity measurements (17, 19, 21, 179 and 182 GHz) into an integrated water vapor profile up to 14 km tangent altitude. The algorithm is based on the estimate of the SNR (Signal to Noise Ratio) at the receiver, so as to exploit adaptively at every tangent altitude the optimal channel, based on actual signal conditions.

In this work we present a software simulator for the performance evaluation of the NDSA (Normalized Differential Spectral Absorption) method at global scale assuming a realistic satellite orbital plane with two counter rotating satellite. The software tool processes atmospheric vertical profiles (pressure, temperature, water and liquid contents). The software simulator accounts for the main disturbance effects: scintillation impairments, thermal noise at the receiver and defocusing. The microwave propagation in atmosphere is simulated by means of the MPM93 model. Performance results about NDSA measurements at global scale for a single day at 17.25 and 20.20 GHZ are presented and discussed.

In this paper, we propose a novel remote sensing method that is adequate for rainfall rate measurements in real time by means of tomographic processing applied to power attenuation measurements made across the microwave links defined by radio base station networks for mobile communication systems. A description of the tomographic algorithms we developed is presented together with some simulation results. These concern rainfall rate estimation applying such algorithms to the current radio base station arrangement over the city of Florence, Italy, while the rainfall field is simulated through weather radar data.

A measurement approach for estimating the emission flux by gas soil sources, based on the use of IR laser measurements over optical links and atmospheric diffusion models is presented. An ad hoc disposition of the optical links close to the emission area allows the tomographic estimation of the gas concentration over a closed surface corresponding to an air volume that covers the emission area. The real time concentration measurements over this closed surface allow us to estimate the emission flux of the emission area, once the atmospheric diffusion conditions are known. In this paper, we present some simulation results assuming that the plane surfaces where laser measurements are made are the faces of a parallelepiped. Simulations are based on diffusion models where the air diffusion and transportation phenomena are due to the horizontal wind.

Normalized differential spectral attenuation (NDSA) is a novel differential measurement method to estimate the total content of water vapor [integrated water vapor (IWV)] along a tropospheric propagation path between two low Earth orbit (LEO) satellites. A transmitter onboard the first LEO satellite and a receiver onboard the second one are required. The NDSA approach is based on the simultaneous estimates of the total attenuation at two relatively close frequencies in the Ku/K-bands and of a "spectral sensitivity parameter" that can be directly converted into IWV. The spectral sensitivity has the potential to determine the water vapor contribution, to cancel out all spectrally flat unwanted contributions, and to limit the impairments due to tropospheric scintillation. In this paper, we focus on the measurement accuracy of the spectral sensitivity parameter. Specifically, we examine this accuracy at three different frequencies and for two models of atmospheric structure. We first provide an approximate expression of the accuracy and then validate this expression through Monte Carlo simulations based on microwave propagation models.

The NDSA method is a novel differential measurement way for estimating the total content of water vapor (IWV, Integrated Water Vapor) along a tropospheric propagation path between two Low Earth Orbit (LEO) satellites. NDSA is based on the simultaneous measurement of the total attenuation at two relatively close frequencies in the Ku/K bands, and on the estimate of a "spectral sensitivity parameter" that can be directly converted into IWV. NDSA is potentially able to emphasize the water vapor contribution, to cancel out all spectrally flat unwanted contributions and to limit the impairments due to tropospheric scintillation. In this paper we focus on the measurement accuracy of the spectral sensitivity parameter. Specifically, we examine such accuracy at three different frequencies and for two models of atmospheric structure.

In this work we summarize some of the results obtained using a portable IR laser device during measurement campaigns of CO2concentrations in air from different environmental sites characterized by gas emissions. The IR laser measurements for the remote sensing have been carried out in volcanic, geothermal, industrial and waste disposal areas. The measurement methods we are developing, based on gas concentration measurements in air by IR laser devices on optical links, seem to be particularly suitable when CO2gas emissions cannot be measured by means of other reliable methods.

We introduce here the normalized differential spectral attenuation (NDSA) approach, which is a novel differential measurement way for estimating the total content of water vapor integrated water vapor (IWV) along a tropospheric propagation path between two Low Earth Orbit (LEO) satellites. The NDSA approach requires a transmitter onboard the first LEO satellite and a receiver onboard the second one. It is based on the simultaneous measurement of the total attenuation at two relatively close frequencies in the Ku/K bands, and on the estimate of a "spectral sensitivity parameter" that can be directly converted into IWV. NDSA is potentially able to emphasize the water vapor contribution, to cancel out all spectrally flat unwanted contributions and to limit the impairments due to tropospheric scintillation. The objective of the paper is to analyze the level of correlation between the spectral sensitivity parameter and the IWV at a given altitude from ground of the LEO-LEO link (tangent altitude), in order to single out the best performing frequencies. Simulation results are based on microwave propagation models and on radiosonde data. The results shows the potential of the NDSA approach to provide direct estimates of IWV along LEO-LEO tropospheric propagation paths in the 15-25 GHz frequency range, under different atmospheric conditions.

A theoretical analysis of the impact of clear-air tropospheric scintillation on a radio occultation link between two low Earth orbit satellites in K- and Ku-bands is presented, with particular reference to differential approaches for the measure of the total content of water vapor. The troposphere is described as a spherically symmetric turbulent medium satisfying Kolmogorov theory. Rytov's first iteration solution for weak fluctuations is used to derive an expression for the variance of amplitude fluctuations of the wave as well as their spectrum and the correlation between fluctuations at different frequencies. The validity of the assumptions made and the influence of atmospheric parameters on the quantities of interest are also investigated and discussed. Finally, numerical results are presented to provide an estimate of the level of scintillation-induced disturbances

In this work we present the simulation results concerning the possibility to estimate the tropospheric water vapor content along the propagation path between two satellites counter-rotating on two different LEO orbits. The estimation method is based on the measurement of a parameter referring to the differential spectral absorption at 17.25 GHz along the propagation link between the two satellites. The choice of that frequency allows to estimate the water vapor in the lowest troposphere, namely when the propagation path crosses the troposphere at tangent altitudes up to 6 km above the Earth's surface. Effects of different latitudes and atmospheric bending have been accounted for and are presented and discussed.

In this work we propose a procedure for the estimation of the spatial distribution of the rainfall rate in the observation time T over an area covered by a meteorological radar and a raingauge network. T can be the whole duration of a rainfall phenomenon or a part of it. The procedure is applied to a data set composed by PPI scans of absolute reflectivity gathered by a weather radar and by point rainfall measurement as provided by a raingauge network over the area monitored by the radar. The procedure was applied and tested on a experimental dataset related to a one-day precipitation phenomenon observed in Tuscany (Italy) on 29 October 1999, along the Arno river basin. The performance of the proposed procedure has been evaluated assuming a subset of the raingauge network as "true" rainfall rate reference

We propose the utilization of a satellite system, composed by a couple of LEO (low Earth orbit) satellites operating in the 18-22 GHz range (close to the 22.235 GHz absorption line of water vapor), to estimate the total content of water vapor (IWV, integrated water vapor) along the propagation path between the two satellites (one of them carrying a transmitter, the other a receiver). In particular, we show that IWV can be estimated starting from measurements of received spectral power.

Abstract- In this paper we will present the results of the trade studies on the performances of a spacebome Doppler radar in measuring vertical rainfall velocity. Particular emphases will be placed on: 1) the choice of the PRF vs. antenna size ratio, 2) the choice of the observational strategy, 3) the choice of the operating frequency; and the 4) processing strategy. The results show that accuracies of 1 m/s or better can be achieved with the currently available technology and with careful selection the system parameters. 1.

The southern area of Italy is characterized by the presence of many active volcanic areas. In Pozzuoli (Naples, Italy), an urban area characterized by high volcanic risk, a gas emitting site is present. A high percentage of CO/sub 2/ is emitted, whose atmospheric concentration measurement is an important task in many environmental and scientific applications. In this paper, we describe the utilization over that area of a mobile infrared (IR) laser system, able to measure the CO/sub 2/ concentration along rectilinear atmospheric paths up to 1-km length, and the result of tomographic processing applied to retrieve a two-dimensional CO/sub 2/ concentration field. The laser system computes the link averaged concentration by processing the received IR laser radiation propagated along an open-air rectilinear link connecting the transmitter/receiver laser unit and a passive retroreflector device. A one-day measurement campaign has been made and 15 different atmospheric propagation links were considered moving the transmitter/receiver unit and some retroreflectors.

In this paper we report the first simulation-based results concerning the potential of a CW radar system for differential attenuation measurements around 19 GHz. The objective is the estimate of the columnar water vapor from a LEO satellite or from airplanes carrying a nadir pointing radar system. Simulations are based on a microwave propagation model for atmosphere, radiosonde data, and ground backscattering cross section models. The correlation between the radar output and the columnar water vapor is shown.

The objective of this paper is to proceed, by investigating the statistics of simulated measurements based on a large dataset of radiosonde profiles, to assess the feasibility of active systems providing water vapor profile information based on Earth-satellite multifrequency differential attenuation measurements made in the 18-22-GHz range. Recently, in fact, we pointed out the potential and the advantages of such measurements, showing in particular how a spectral sensitivity parameter could be exploited to provide the total water vapor content and further information about the shape of its vertical profile. In this work, we present an in-depth statistical analysis of the relationship between the spectral sensitivity parameter and the water vapor content at different tropospheric layers. Furthermore, we discuss the performance of a simple amplitude modulation transmit-receive system that could be adopted to provide the sensitivity measurements. It is shown that a dual-frequency system can directly provide with good accuracy the columnar water vapor content separately from the content of the 3-9 km atmospheric layer.

The authors describe a differential method for estimating mean concentrations of atmospheric molecular components along a quasivertical rectilinear Earth-air path utilizing a transmitter-receiver pair operating at infrared. The choice of a differential method is due to the need to limit calibration problems without utilizing more complex and costly systems such as DIAL, whose capabilities are definitely oversized for this kind of measurement. For this objective, a preliminary selection of the optimal wavenumbers for each molecular species of interest is needed. This is the main issue discussed in this paper, after which the analysis focuses on the effects of the uncertainties on atmospheric parameters that need to be estimated to provide the final mean-concentration estimates. The feasibility study is carried out on carbon monoxide, considered as test species of interest in the reported simulations of atmospheric propagation, based on standard atmospheric models. Technological requirements are finally discussed.

The authors address the problem of estimating vertical profiles of atmospheric water vapor by means of attenuation measurements simultaneously made at different frequencies along a vertical satellite-ground link. The operating frequencies selected are those around the spectral absorption lines of water vapor at 22.235 GHz. A simulation is presented of multifrequency attenuation measurements, based on an atmospheric propagation model and on radiosonde data providing true profiles of temperature, pressure, and water vapor. The results indicate that such multifrequency measurements are correlated to variations of the vertical profiles of water vapor. It is therefore expected that vertical detail of such profiles depends on number and position of the frequencies utilized.

In this paper, we analyze the feasibility and performance of a particular tomographic system for atmospheric pollution monitoring over limited areas (e.g., urban areas). Such a system exploits attenuation-based infrared measurements of the average concentration of the fundamental molecular species of pollutants along rectilinear paths. First, the paper demonstrates the feasibility of an apparatus based on semiconductor infrared laser diode transmitters and passive retroreflectors, capable of measuring the average concentration of pollutants along rectilinear paths with 2-km maximum length, by exploiting their infrared absorption properties. For each gaseous species of interest, the optimal wavelength is then singled out, with the purpose of applying the derivative method for measuring the corresponding average atmospheric concentration. The optimal wavelengths are determined based on both absorption data of atmospheric components and plausible ranges of variation of their concentration. Finally, we present simulations carried out to evaluate the reconstruction of spatial-concentration fields of several air pollutants obtained through a tomographic-inversion algorithm exploiting simultaneous attenuation measurements made along different infrared links. Two different network topologies for such measurements are considered.

The authors analyze the feasibility and performance of a particular tomographic system for atmospheric pollution monitoring over limited areas (e.g. urban areas). Such a system exploits attenuation-based infrared measurements of the average concentration of the fundamental molecular species of pollutants along rectilinear paths. First, the paper demonstrates the feasibility of an apparatus based on semiconductor infrared laser diode transmitters and passive retroreflectors, capable of measuring the average concentration of pollutants along rectilinear paths with 2 km maximum length, by exploiting their infrared absorption properties. For each gaseous species of interest, the optimal wavelength is then singled out, with the purpose of applying the derivative method for measuring the corresponding average atmospheric concentration. The optimal wavelengths are determined based on both absorption data of atmospheric components and plausible ranges of variation of their concentration. Finally, the authors present simulations carried out to evaluate the reconstruction of spatial concentration fields of several air pollutants, obtained through a tomographic inversion algorithm exploiting simultaneous attenuation measurements made along different infrared links. Two different network topologies for such measurements are considered.

The microwave tomographic inversion technique (MTIT) proposed in 1991 for reconstruction of rainfall fields at ground through microwave attenuation measurements is reconsidered. A new algorithm for data inversion is presented [referred to as stochastic reconstruction technique (SRT)] that generally performs better than the one originally adopted [referred to as arithmetic reconstruction technique (ART)]. Improvement is achieved in spatial definition and general reliability of rainfall field reconstruction. The new model adopted to represent the reconstructed rainfall fields leads to a completely different strategy for the inversion problem, and this strategy is based on a global optimization stochastic technique (GOST). Results obtained through the SRT-MTIT are presented in the paper and compared to those obtained by employing the ART-MTIT. It also is shown that, based on the SRT-MTIT approach, fast and reliable time tracking of rainfall events is made possible by exploiting previous reconstructions and by the improved long-term physical consistency of the model adopted for rainfall field decomposition.