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Activity title

Turbulence mitigation for Electro Optics (EO) and laser systems

Activity Reference

SET-226

Panel

Sensors & Electronics Technology

Security Classification

NATO UNCLASSIFIED

Status

Active

Activity type

RTG

Start date

2015

End date

2019

Keywords

Adaptive Optics, Image, Laser Beam, Modeling, Optical Turbulence, Performance Improvement, Propagation, Quality Metric, Target in the Loop

Background

High performance optical systems suffer from atmospheric turbulence effects, limiting range and resolution. Depending on the application (e.g., imaging or laser beam delivery), techniques can be implemented to mitigate its effects. Adaptive Optics systems are more efficient for laser beam delivery systems, while data processing is more suitable for visible/IR imaging sensors. During the TG SET 165, experimental data (extended targets and laser sources images with a propagation distance of 7 km) were recorded. Data processing was focused on turbulence characterization and image processing. The conclusions are: 1) Over this propagation distance, using developed formalism (Kolmogorov behavior and Rytov approximation) seems to be a good approach to quantify turbulence impact. 2) Criteria were proposed to compare different techniques of image processing and quantify the improvement. In weak turbulence, proposed techniques give good improvement in image quality (i.e., remove motion and decrease blur). However, in most of cases, we have to deal with stronger turbulence conditions and longer propagation distances. Turbulence near the ground depends strongly on many variables, including sunlight, soil nature and humidity of the air. Over long distances, a great variability of environmental conditions can be found. Is it important to know them with a great accuracy? Which turbulence parameters are relevant? What is their influence on system performance? A better knowledge of turbulence impact can help to optimize turbulence mitigation techniques and model system performance.

Objectives

The objective is to improve our knowledge on the impact of turbulence on EO system performance in order to propose adequate mitigation techniques. The goals are: • Comparison, side by side, both experimentally and numerically, of different : o Adaptive Optics (AO) techniques (fiber arrays and conventional AO for example) o Wave-Front sensing (WFS) techniques in strong scintillation regime including Shack-Hartmann, holographic WFS and MAPR (Multi-aperture phase reconstruction) sensor o Image processing techniques for turbulence effects mitigation for different turbulence conditions at short and long ranges • Validation of simulation tools by comparing numerical results to experimental ones. • Experimental tests of real-time image processing under different turbulence conditions A trial will be organized to collect data and test real-time image processing.

Topics

future task could be formed around calculating the average probability of correctly identifying military vehicles before and after turbulence restoration. Additionally, in a future experiment, fixed aberrations within the optical system should be reduced and isolated (via laboratory measurements) from turbulence effects.

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