Mitigation Of Atmospheric Effects Research Articles

An alternative to derive ionospheric and tropospheric SSR corrections for PPP-RTK using adaptive constraints

PPP-RTK (Precise Point Positioning – Real Time Kinematic) is a positioning method by GNSS (Global Navigation Satellite Systems), based on the SSR (State Space Representation) concept. One challenge for the fast convergence of PPP-RTK solutions in real-time applications is the mitigation of atmospheric effects (troposphere and ionosphere). Thus, using atmospheric models, PPP solutions can achieve accurate positions and shortened initialisation time. Such performance depends on the topology of permanent station networks and atmospheric conditions. The main objective of this contribution is to study the PPP-RTK and the optimised infrastructure in terms of costs and benefits to realise the method using atmospheric corrections.

H∞ controller design for the mitigation of atmospheric effects on the laser beam pointing

In this paper, the control of a fast steering mirror, which is the core element of an adaptive optics system, is investigated to suppress the beam jitter. The main source of the jitter is taken as the atmospheric turbulence. The effect of the atmospheric turbulence on the beam jitter is experimentally determined with respect to the two different refractive index structure parameters. The mathematical model of the fast steering mirror based on the atmoshperic turbulence data is obtained using the system identification. In order to overcome implementation problems, the low order proportional-integral-derivative (PID) type controllers, which minimize the [Formula: see text] norm of the closed loop system, are designed in the centralized and the decentralized settings. In addition to this, the fixed order weighted [Formula: see text] controller is based on the frequency characteristics of the atmospheric turbulence that is determined experimentally. Then, in order to show the effectiveness of the proposed low order PID type controller, the designed controllers are compared on the experimental setup. Finally, the simulation and the experimental results are presented. Comparison of advantageous and disadvantageous of centralized and decentralized controller architectures are discussed.

Fusion of adaptive beam steering and optimization-based wavefront control for laser communications in atmosphere

The performance of mobile laser communication systems operating within Earth's atmosphere is generally limited by the pointing errors due to movement of the platforms and mechanical vibrations. In addition, atmospheric turbulence causes changes of the refractive index along the propagation path, creating random redistribution of the optical energy in the spatial domain. Under adverse conditions these effects lead to increased bit error rate. While traditional approaches provide separate treatment of these problems, suggesting high-bandwidth beam steering systems for tracking and wavefront control for the mitigation of atmospheric effects, the two tasks can be integrated. This paper presents a hybrid laser beam-steering–wavefront-control system comprising an electrically addressed spatial light modulator (SLM) installed on the Omni-Wrist sensor mount. The function of the Omni-Wrist is to provide coarse steering over a wide range of pointing angles, while that of the SLM is twofold: wavefront correction and fine steering. The control law for the Omni-Wrist is synthesized using a decentralized approach that provides independent access to the azimuth and declination channels; calculation of the required phase profile for the SLM is optimization-based. This paper presents the control algorithms, the approach to coordinating the operation of the two systems, and the results.