STK 12.2 Spotlight: MODTRAN-based Propagation

Before STK 12.2, our laser propagation model was limited to a Beer-Bougher-Lambert model, which consists of extinction coefficients for concentric layers of the atmosphere. The problem is that many of our customers don’t have access to extinction coefficients to populate the model. However, our EOIR capability makes use of a MODTRAN-based lookup table that represents the atmosphere for visual and near visual wavelengths. So, starting with STK 12.2, we made this accessible to laser communications as another propagation model.

Free space optics versus RF

Free space optics (FSO) is a communications methodology that uses infrared, visual, and up into ultraviolet frequencies to transfer information through the air and space. FSO communications have been relied upon for decades and provide numerous benefits over RF communications. FSO advantages over RF include a larger bandwidth, faster transmissions, resiliency to jamming, low probability of detection and interception (LPD/LPI), and more.

As the launch-to-target ranges and the speeds of threats increase, it follows that reaction times to these threats decrease. This decrease in reaction time requires that critical information be delivered with reduced latency. And, as threats decrease in size, higher fidelity sensor are required. But, higher fidelity sensors produce more information, which requires larger bandwidths to transfer the data. To meet these objectives, solution providers are using FSO rather than RF technology.

Lasers, with their large bandwidths, can meet stringent low latency, high data rate, and communication needs. Laser communications achieve data throughputs at rates 10 to 100 times faster than RF systems. FSO systems are appearing on all types of platforms. The space, weight, and power considerations are even able to provide high speed laser communications for UAVs as well as CubeSats.

Another advantage laser communications have over RF is that lasers provide a low probability of detection and interception (LPD/LPI), making them a secure method of communications. Laser systems use a very condensed and narrow beam that has little divergence compared to RF technologies. Thus, to intercept one you would need to maneuver into a very small beam and, if these are mobile platforms, you would have to maneuver as the intended system maneuvers. Couple that with the stringent alignment requirements and it is very difficult to intercept information. Even if something was able to maneuver into position, cryptographic protocols at the quantum level such as Quantum Key Distribution (QKD) provide indicators that the stream is being disturbed.

Modeling atmospheric conditions

Use of lasers is not without its complexities and shortfalls. Because of the very narrow beams, precise tracking is required. Even if accurate tracking is accomplished, any obstructions will prevent and thus degrade system performance. One of the biggest factors troubling laser communications is the atmosphere — including dust, contaminants, clouds, rain, fog, and weather turbulence. The better we can model the atmosphere, the better we can predict system performance.

Once the atmosphere is accurately modeled, we can consider the spatial-temporal dynamics of objects within that atmospheric state and the spatial-temporal dynamics of the objects within a spatial-temporal atmosphere.

Atmospheric models such as MODTRAN model the current “static” conditions of the atmosphere. Bringing models into STK not only enables you to quickly understand the spatial-temporal dynamics of platforms and payloads within a static atmosphere, but also predict system performance under dynamic spatial-temporal atmospheric conditions.