KEYWORDS: Free space optics, Visibility through fog, Visibility, Mid infrared, Data modeling, Signal attenuation, Attenuation, Atmospheric propagation, Wave propagation, Near infrared
A Free-Space Optics (FSO) propagation experiment is running in Milan, Italy, since September 2022, in the framework of the Joint Lab between Huawei and Politecnico di Milano in collaboration with Consiglio Nazionale delle Ricerche (CNR). The set-up includes two co-located FSO links: a prototype mid-IR link (10.6 μm) and a commercial near-IR link (1.550 μm) over an 800-m path. Meteorological data are collected by two visibility sensors, two disdrometers, and a weather station. Data from a case study of moderate fog that occurred in winter 2022 highlights that the spatial distribution of fog is highly non-homogeneous along the path, hence, simple prediction models based on single-point measurements of the visibility may incur in large errors. Moreover, the comparison of path attenuation time series shows that the mid-IR link performs better than near-IR.
This contribution investigates the effectiveness of optical communication links in enabling high-speed
data transfer from deep-space (DS) probes directly to Earth ground stations. In particular, the propagation
impairments induced by clouds are estimated by exploiting long-term radiosonde observation data collected
in some European sites. The impact of different cloud types on optical links operating at 1.55 μm is first quantified
in terms of total path attenuation, and afterward, the implementation of multisite diversity schemes is discussed
to counteract the extremely high attenuation levels caused by clouds. Results show that a three-site diversity
system with target availability of 90% allows reduction of the link margin to counteract cloud attenuation from at
least 40 dB to ∼6 dB, which makes optical communications a viable option also for DS missions.
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