Luke K. Rumbaugh

Statistical backscatter suppression technique for a wideband hybrid lidar-radar ranging system

A new backscatter suppression technique is applied to a wideband modulation scheme to enhance optical ranging in underwater environments. The statistical digital signal processing (DSP) approach of blind signal separation (BSS) [1-2] is applied to a frequency domain reflectometry (FDR) [3-4] ranging system. Applying BSS to the FDR system allows the backscatter return to be dynamically measured and cancelled out before computing range. Results from simulations and laboratory experiments are presented to demonstrate the combined FDR/BSS approach.

Underwater optical impulse response measurement using a chaotic lidar sensor

This paper explores the use of a recently developed chaotic lidar sensor to perform impulse response measurements underwater. The sensor’s measured system impulse response, which approximates a thumbtack function with a 1 ns peak width, is used with an ocean impulse response simulator to predict the chaotic lidar’s expected performance underwater. A calibration routine is developed to compensate for the finite resolution and sidelobes in the sensor’s system impulse response, improving the accuracy of the simulated chaotic lidar results. In an example application of water turbidity measurement, the extinction coefficient of water, c, is extracted from simulated chaotic lidar impulse responses with an average error of 0.03/m over a range of turbidities from c=0.1/m to c=0.3/m. Simulations are also presented to demonstrate that the chaotic lidar sensor impulse response can simultaneously detect multiple reflective elements and the volumetric backscatter response with a 1 ns temporal resolution. Laboratory water tank measurements are performed to validate the simulation approach, and the experimental chaotic lidar measurements are in reasonable agreement with the simulated results.

Wide bandwidth source for high resolution ranging

An erbium-doped fiber ring laser with a 1 km-long resonator cavity is presented as an instantaneous wideband source for high-resolution lidar and radar. This signal source has a high bandwidth and a uniform spectrum, desirable qualities for high performance correlation-based ranging. A microwave bandwidth photodetector is used to convert the optical signal to an electrical signal with 4 GHz of bandwidth, whose spectral flatness is seen to be +/- 2 dB.

Underwater object detection performance of a chaotically modulated laser rangefinder

This paper derives system performance for a chaotically modulated laser rangefinder operating in turbid water, both as a function of rangefinder parameters and as a function of water and target characteristics. An ocean impulse response simulator is used to calculate signal-to-noise-ratios and target detection performance at a variety of water turbidities and target ranges. The use of a digital filter chain is demonstrated, and its effect on system performance is considered. The use of an optical backscatter-removal filter is proposed, and its potential effect on system performance is considered.

A mixed numeric and analytic method for investigating OAM beam scattering in turbid water

A mixed numerical and analytical technique is presented to investigate OAM beam scattering in turbid water. Single particle scattering from an OAM beam in an underwater environment is computed numerically using COMSOL Multiphysics Modeling Software to generate single scattering functions. The array theorem extends this single scattering function to multiple scatters in a three dimensional space. Simulations predict that OAM illumination reduces forward scattering in low turbidity environments compared to scattering from Gaussian beams. In high turbidity water, scattering results from OAM beams and Gaussian beam converge. Experimental results are presented that are consistent with predictions from simulation.

Energy-Harvesting Low-Power Devices in Cyber-Physical Systems

Cyber-physical systems (CPSs) widely use sensors and actors for monitoring and controlling the physical elements of the CPS. Reliability and lifetime of those sensors and actors play an important role in the reliability and availability of the whole system. The limited battery capacity of the sensors and actors emerge as a significant challenge in hyper-connected CPSs, mostly because intense communications in a limited physical space drain batteries faster than conventional sensor applications. Energy conservation and energy harvesting approaches increase the lifetime of sensors. However, traditional energy harvesting techniques do not serve as deterministic sources of energy due to their intermittent availability. Recently, low-power sensors with radio frequency (RF) energy harvesting capability have become commercially available. In this chapter, we motivate the use of RF-powered sensors in CPSs. The chapter introduces results from RF energy harvesting in sensor networks and in heterogenous wireless networks. In addition, the chapter discusses and presents some preliminary results on relayed energy transfer.

An underwater chaotic lidar sensor based on synchronized blue laser diodes

We present a novel chaotic lidar system designed for underwater impulse response measurements. The system uses two recently introduced, low-cost, commercially available 462 nm multimode InGaN laser diodes, which are synchronized by a bi-directional optical link. This synchronization results in a noise-like chaotic intensity modulation with over 1 GHz bandwidth and strong modulation depth. An advantage of this approach is its simple transmitter architecture, which uses no electrical signal generator, electro-optic modulator, or optical frequency doubler.

Blind signal separation for underwater lidar applications

Blind signal separation (BSS) is demonstrated to improve signal-to-interference ratio (SIR) in underwater light detection and ranging (lidar) applications. Lidar systems are used for high-resolution ranging and imaging underwater. A difficult problem in this area is detecting the return from an object of interest in the presence of a strong “clutter” return caused by backscattering in low visibility water environments. The principal component analysis form of BSS is applied to separate the return into multiple subspaces, with the backscatter subspace suppressed to improve detection capability. Simulations are performed using an underwater optical channel model to simulate a challenging harbor-like environment. We show that the processing gain from BSS is increased when the correlation energy between observations is increased, for example by using closely spaced observations. The SIR gain of BSS is explored as a function of frequency, achieving substantial gain independently of carrier frequency. This result has important implications on the design of lidar systems, suggesting that BSS can be combined with low-cost, low-frequency components to achieve performance similar to systems using high-frequency components.

Backscatter suppression via blind signal separation for a 532 nm underwater chaotic lidar rangefinder

Blind signal separation is applied to suppress backscatter for a 532 nm chaotic lidar underwater rangefinder. When operating in turbid waters, chaotic lidar returns contain information for both submerged objects and an optical backscatter “clutter” component. The statistical digital signal processing technique of blind signal separation (BSS) is applied to dynamically measure and cancel out the backscatter component before computing range to the desired object. Results from simulations and laboratory experiments are presented to demonstrate the combined chaotic/BSS approach. The chaotic/BSS approach extends operating range by almost 40% and achieves centimeter-order range accuracy. Receiver operating curves are simulated for the chaotic/BSS approach, which show convergence towards the ideal classifier in several conditions of interest.

A wideband noise-like transmitter approach for underwater lidar using diode lasers and passive fiber optic processors

A new wideband noise-like transmitter approach is presented for high resolution underwater lidar sensing. The transmitter approach is based on small-footprint, low-cost components, using low coherence time laser diodes and passive fiber processors to generate wideband noise-like intensity modulation signals in the blue-green optical spectrum. Prototype transmitters are demonstrated using both blue and green laser diodes with passive fiber interferometer structures. Laboratory water tank experiments using a two-diode 516/518 nm prototype transmitter show centimeter range error and 30 cm range resolution while detecting a submerged gray target in up to ten attenuation lengths of turbid water. Experimentally observed challenges for target rangefinding are discussed, including shot noise, backscatter returns, and self-clutter. Strategies are proposed to mitigate these challenges and enhance performance when operating at long standoff distances in turbid waters.