Frank Marzano’s research while affiliated with Sapienza University of Rome and other places

Free Space Optics (FSO) technology enabling next-generation near-Earth communication is prone to severe propagation losses due to atmospheric-turbulence-induced fading and Mie scattering (clouds). As an alternative to the real-time evaluation of the weather effects over optical signal, a state-of-the-art laboratory testbed for verification of slant APD-based (Avalanche Photodiode) FSO links in laboratory conditions is proposed. In particular, a hardware channel emulator representing an FSO channel by means of fiber-coupled Variable Optical Attenuator (VOA) controlled by driver board and software is utilized. While atmospheric scintillation data are generated based on Radiosonde Observation (RAOB) databases combined with a statistical design approach, cloud attenuation is introduced using Mie theory together with empirical Log-Normal modeling. The estimation of atmospheric-turbulence-induced losses within the emulated optical downlink is done with an FSO IM/DD prototype (Intensity Modulation/Direct Detection) relying on two different data throughputs using a transmitter with external and internal modulation. Moreover, the receiver under-test is a high-speed 10 Gbps APD photodetector with integrated Transimpedance Amplifier (TIA) typically installed in OGSs (Optical Ground Stations) for LEO/GEO satellite communication. The overall testbed performance is addressed by a BER tester and a digital oscilloscope, providing BER graphs and eye diagrams that prove the applied approach for testing APD-TIA in the presence of weather-based disruptions. Furthermore, the testbed benefits from the used beam camera that measures the quality of the generated FSO beam.

The forthcoming spaceborne ice cloud imager (ICI) millimeter/submillimeter-wave radiometer is designed to support climate monitoring and ice clouds representation in weather and climate models. The assessment of the correct pointing of each ICI channel is of undeniable importance to deliver high-quality products. Nevertheless, the ICI channels have a limited chance to sample the surface features due to the strong atmospheric gas absorption. Only for channels within 183–325 GHz, few locations worldwide show the sufficiently dry environmental conditions allowing for an occasional sampling of surface landmark targets. In this work, for the first time, we investigate the possibility of exploiting distinctive atmospheric signatures, namely, those generated by water vapor masses and deep convective clouds, for absolute and relative geolocation validation purposes. The main idea behind the proposed approach is: 1) to georeference a pivotal channel at 183 GHz, exploiting the synergy of infrared and microwave collocated observations (absolute geolocation) and 2) to test the relative pointing accuracy of all the other ICI channels with respect to the pivotal one (relative geolocation). Observations of the Special Sensor Microwave Imager/Sounder (SSMIS), the Spinning Enhanced Visible and Infrared Imager (SEVIRI), and radiative transfer simulations are used to pursue the goals. Results show that water vapor mass (WVM) atmospheric targets can achieve an absolute point accuracy for the lower ICI channels of the order of 5.1 km (i.e., 32% of the 16-km footprint size). Conversely, when dealing with the relative pointing accuracy of higher ICI channels, the expected pointing accuracy is smaller than 4.1 km (i.e., 25% of the footprint size).

Free space optics (FSO) is a wireless optical communication technology enabling extremely high data transmission rates, which can be used for a wide range of emerging applications. Nevertheless, FSO system reliability can be easily deteriorated in the presence of various weather-induced disruptions. The main two atmospheric effects influencing FSO links are fog and turbulence. Their investigation is based on real data and simulations—separately performed for two different locations in Austria. Based on the aforementioned weather-induced disruption analysis and existing knowledge about the link margin of the selected FSO communication measurement scenario, both outage probability and availability parameters are evaluated. Considering these outcomes, the most prominent and well-established atmospheric mitigation techniques for FSO technologies are explained. To address these techniques, a special emphasis is placed on two emerging applications: modern deep space communications as well as vehicle-to-vehicle (V2V) wireless optical communications. Both are examined based on their susceptibility to the investigated weather-induced disruptions. In order to improve the deep space FSO system resilience against long-distance and atmospheric effects, an approach using the superconducting nanowire single-photon detector (SNSPD) technology is considered. Furthermore, a hybrid V2V communication solution based on radio frequency (RF) and FSO is described.