LabRadioMet

LabRadioMet OBJECTIVES

The Laboratory of RadioMeteorology (LabRadioMet) is a joint initiative of DIET, FUB, and CETEMPS to exploit ground-based remote sensing of the atmosphere in synergy with microwave radiocommunication and satellite meteorology. Its first activity dates back to 1980 (thanks to an initiative of Prof. d'Auria and his colleagues) and is coordinated with the Laboratory of Antennas, Radiopropagation and Telesensing (LabART) of DIET.

The LabRadioMet current research concerns passive and active remote sensing of the atmosphere from ground-based instruments, with a particular focus on clouds and precipitation using microwave data, development of inversion methods, and radiative transfer modeling of absorbing and scattering media. Other main topics of interest are radar meteorology for rain, wind and ash retrieval. The LabRadioMet is also deeply involved in radiopropagation studies, including e.m. field scintillation and rain fading modeling and data analysis along satellite microwave and millimeter-wave links.

The LabRadioMet has the following objectives:

1. to manage ground-based remote sensing and in situ instrumentation;

2. to design and develop new microwave remote sensing instrumentation;

3. to develop advanced algorithms for ground-based weather radar retrieval;

4. to develop advanced algorithms for ground-based microwave radiometric retrieval;

5. to pursue the use of remote sensing data for radiocommunication and deep-space applications;

6. to pursue the use of numerical weather prediction models for radiocommunication and deep-space applications;

7. to operate as a ground-based facility for satellite product validation.

The LabRadioMet board includes:

• F.S. Marzano (DIET, Sapienza UniRome & CETEMPS)

• F. Consalvi (FUB, Rome)

• S. Barbieri (DIET, Sapienza UniRome & CETEMPS)

• P. Cicolin (DIET, Sapienza UniRome)

• M. Biscarini (DIET, Sapienza UniRome)

• D. Comite (DIET, Sapienza UniRome)

• N. Pierdicca (DIET, Sapienza UniRome)

1. Ground-based microwave radar meteorology

Rain, snow, and volcanic ash clouds contain particles generated by different physical and chemical processes. When electromagnetic radiation interacts with particle distribution, causing absorption and scattering, the backscattered power enables the retrieval of useful geophysical parameters of particle distribution. This article is the measurement principle of microwave weather (meteorological) radar, monostatic remote sensing that can exploit Rayleigh and Mie backscattering to remotely probe atmospheric clouds. An overview of weather radar systems and data processing for rain, snow, and volcanic ash clouds focusing on ground-based weather radars along with airborne and spaceborne configurations.

Signal processing of single-polarization weather radar systems in addition to more advanced schemes, such as those that enable Doppler and dual-polarization capability, are discussed. Additionally, we describe Doppler weather radars with narrow beams, which are used to detect low-level wind shear during rain, microbursts, and gusts. Multifrequency radar for snowfall retrieval is also presented, with an emphasis on estimation and classification of the microphysical properties of particles. Finally, future directions for signal processing and applications for microwave weather radar systems are presented.

2. Ground-based microwave radiometry for remote sensing and radiopropagation

Sun-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 millimeter-wave and submillimeter-wave frequency region, especially where experimental data from beacon receivers are not available. This paper summarizes what above.

3. Atmospheric propagation at microwave, millimeter-wave, and optical wavelength

The aim is to investigate the usability of high-frequency channels for LEO/MEO (Low/Medium Earth Orbit) satellite communications and deep-space (DS) transmissions exploiting radiometeorological forecast modeling. A previously developed model chain for DS link-budget optimization, based on numerical weather forecasts (WFs), is adopted. Exploiting the available WF-based methodology, we compute DV return for DS missions operating at X-, K-, Ka-, Q-, and W-bands in order to make a comparative study of the behavior of DS transmission-channels at these frequencies. Results in this work show that, in terms of received DV, an innovative WF-based approach is more convenient than traditional methodologies and exhibits a trend similar to the benchmark (ideal case).

Free space optics (FSO) channel availability is affected by atmospheric water particles, which may introduce severe path attenuation. A unified microphysically oriented atmospheric particle scattering (MAPS) model is proposed and described to simulate particle scattering effects on FSO links. Atmospheric particles, such as raindrops, graupel particles, and snowflakes, together with fog droplets, are considered. Input data to characterize liquid and frozen water particle size distribution, density, and refractivity are derived. Scattering, absorption, and extinction coefficients as well as the asymmetry factor are numerically simulated for each particle class and then parametrized with respect to particle water content, fall rate, and visibility, spanning from visible to infrared wavelengths.

LabRadioMet MEASUREMENT FACILITY

The Laboratory of Radio Meteorology is placed on the roof terrace of the Faculty of Engineering of the Sapienza University of Rome. The test site is exactly located in ROME, Italy at Latitude 41° 53’ 37 N, Longitude 12° 29’ 38 E.

The position of the Laboratory is amazing as it is on the top of the highest historical hills of Rome, Colle Fagutal. The view of the old city of Rome is unique, but also the optical visibility is very attractive both toward the Tyrrhenian sea and the Apennine range. The LabRadioMet enumerates both in situ meteorological instrumentation coupled with microwave and optical sensors.