sUAS-Based Payload Development and Testing for Quantifying Optical Turbulence

Understanding how atmospheric effects can impact operational conditions is important to the development of High Energy Laser (HEL) weapon systems.

The NPS Penguin small unmanned aerial system used to measure turbulence within the boundary layer.

August 1, 2020

Naval Postgraduate School, Monterey, California

Within the highly dynamic and hostile modern-day battlespace, the Department of Defense (DoD) is constantly facing threats from multiple domains. Unmanned aerial vehicles (UAV), swarms of fast attack craft, anti-ship missiles and manned aircraft are quickly developing asymmetric options. These threats need to be tracked, engaged and destroyed in quick succession. However, not all threats can necessarily be paired with the same weapons system.

The use of directed electro-optical energy has a long history in warfare dating back to the days of the Romans. According to legend, Archimedes used an array of mirrors to direct beams of sunlight on enemy ships to burn them down before they could invade Syracuse. In more recent times, the Navy began experimenting with the use of chemical lasers in the 1970s. Unfortunately, these early attempts were only experimental and never were put into operational use. Their size was too vast to be employed on ships, vehicles or aircraft.

Over time however, as laser technology improved and shifted from chemical lasers to solid state, their size diminished. They are beginning to become employable on several DoD assets. Currently, the Navy uses many different weapons platforms including the Phalanx CIWS, M242 Bushmaster cannon and BAE Systems Mk 45 5-in gun to neutralize symmetric threats.

To complement these weapons platforms, the Navy is developing the AN/SEQ-3 laser weapon system (or XN-1 LaWS). In other forces of the DoD, the Army conducted a test of a high-energy laser (HEL) system onboard an AH-64 Apache attack helicopter and the Air Force is forging ahead with their self-protect high energy laser demonstrator (SHiELD) program which they hope will help to defend its fighter planes.

There are many benefits of adding a laser system to the current array of defenses. Some of these include target cycling time, low shot cost, and tunability. Targets can be taken out in quick succession as each shot only requires a matter of seconds before targeting the next object. The shot is received by the target instantaneously and can be essential for fast moving, inbound targets. Each shot of the laser only requires about a dollar of energy since it is the only “projectile” involved. With the laser system, there is no required storage, disposal, purchase, transport or development of ordnance.

Many of the projectiles of the systems mentioned earlier cost upwards of hundreds of thousands of dollars for every target they engage. Handling the ordnance takes up tight space aboard the ships and maintaining the stockpile is a continuous cycle. Finally, lasers can be tuned in at high enough power levels to vaporize incoming howitzer shells or to docile enough levels enough to simply disable optical sensors onboard a UAV, all within the same system

Unfortunately, despite all the benefits of laser systems, they can be disrupted by atmospheric conditions, over land and over the ocean. The atmosphere is a continually changing mixture of aerosols (dust, salts, etc.) and radiatively active gases such as carbon dioxide and water vapor. Each of these constituents have a direct effect on laser propagation through scattering, refraction and absorption.

In addition to these effects, atmospheric turbulence on very small scales (centimeter to meter), can cause atmospheric scintillation which affects the spreading and coherence of electro-optical propagation. The better we can understand these effects and the makeup of the atmosphere within the battlespace, the more precisely we can predict and mitigate the atmospheric effects on HEL systems. Currently, most atmospheric models work at grid scales of 2 km or greater which are unable to resolve these critical components. Unlike missile and gun-based defense systems which can be projected over the horizon, laser systems are restricted to line-of-sight firing.

The objective of this research, therefore, is to explore the use of small unmanned aerial systems (sUAS) to measure turbulence within the boundary layer to help predict the atmospheric effects on laser propagation.

This work was done by Lee Suring for the Naval Postgraduate School. For more information, download the Technical Support Package (free white paper) below. NPS-0011