Evaluation of Diverged Optics for Optical Multilateration
Kevin N. Stanzione, Eric Bozeman, Nathan S. Barnwell, Elizabeth Izaguirre, Kari Moran, Angelica Sarmiento, Li Sun, NIWC-Pacific
Location: Ballroom B
Date/Time: Thursday, Jun. 15, 11:35 a.m.
Despite the widespread usage of and dependence on GNSS and GPS technologies for today’s military, there remains an intense demand for alternative Position, Navigation, and Timing (PNT) technologies. This presentation will demonstrate the SHOTPUT team’s first-year results for evaluating the use of diverged optics for novel optical positioning systems.
One major advantage optical PNT systems have over radio-based solutions are their adaptability to a wide array of platforms and requirements. While the coverage of an optical system will never be greater in air than that of a radio-based system, its presence can be more selective. Optical time-transfer can be achieved over long distances with collimated optical sources using tracking and pointing. Timing information can also be distributed locally with the use of diverged optics for the receiver and transmitter, relaxing difficult pointing requirements. This can be achieved through lenses, optical arrays, defocusing, and other similar methods of widening the angle at which the optical transmitter can transfer time to the receiver.
A hypothetical network of both elements would retain the advantages of a point-to-point, long distance system as well as a locally dispersed one, to best adapt to platform needs for alternative sources of PNT. We envision such a system that uses high-powered static optical transmitters to form the backbone of this network, providing point-to-point time-transfer. Then, dispersing elements that transmit optical PNT in a wider region to local platforms, such as battlefield equipment and vehicles. While GNSS is available, such a network could rely on GPS-based PNT for timing synchronization. And when it’s not, platforms with optical receivers could use the optical network to provide PNT for critical timing applications.
Time-transfer is the backbone of multilateration, and our team has previously demonstrated optical time-transfer through more than one domain. Our research group has achieved free-space optical time-transfer using infrared light sources, both inside the lab and outside in relevant environments. We have also achieved optical time-transfer through turbid water using a blue-green laser in a lab test setup. This is an interesting domain that radio-based PNT technologies have struggled with, due to the high attenuation of those frequencies in water. Additionally, the attenuation due to the atmosphere also favors higher frequency wavelength’s such as infrared, over radio frequency bands.
The SHOTPUT team at NIWC Pacific is evaluating the use of diverged optics and light sources for optical multilateration. By using a collection of light source transmitters, an optical receiver can be used to determine position through multilateration in real-time. With on-off keying, we have a lab scale optical communications system that transmits digital data to our receiver. This receiver then uses precision timing equipment to accurately measure several of these transmissions to collect time-transfer measurements and psuedoranges in order to calculate a position fix. By using diverged optics, an optical comms and/or PNT system could relax the need for difficult pointing requirements for transmitting data.
This presentation of SHOTPUT will cover different schemes for reducing pointing requirements and their effect on positional accuracy, as well positional error due to clock drift that could arise in environments that lack GPS coverage. Our evaluated results use synchronized and free-running frequency sources to emulate scenarios where GNSS time synchronization is not available to the transmitter network.