Visual inspection of crude oil on water can determine the depth of thin layers of oil. However, catastrophic spills with millimeter (mm) thick oil will just be black, with no visual variation as the oil gets thicker. A day/night heat transfer model was developed to determine crude oil slick thickness. The model uses LWIR thermographic imagery, weather station outputs of air and water temperature, relative humidity, solar radiation, wind speed, other weather input such as cloud cover percent and altitudes, and measured thermal conductivity of Alaskan North Slope (ANS) crude oil. Outdoor field-testing was performed with fresh, weathered, and emulsified ANS crude oils that were placed on water at depths of 2-10 mm. A FLIR T640SC camera viewed the scene from a three-story roof-top to simulate small unmanned aerial vehicle (sUAV) altitudes. A low-cost, portable weather station was set up next to the pool and temperature calibrated LWIR imagery was collected every 15-minutes for 24-hours. The average oil surface temperature was measured for each target. The day/night model predicts oil slick thickness within one or two standard deviations. The fidelity of the thickness measurements is dependent on the accurate measurement of the atmospheric and weather parameters, sea state, heat transfer constants, and calibration and stability of the thermal camera.
MARINE SCOUT is a compact, lightweight, Puma and other small UAS (SUAS) compatible, multi-spectral airborne sensor payload designed to sense and discriminate oil on water (e.g., maritime oil spills), and enable via post-processing the measurement of oil thickness in marine environments. The payload includes near-infrared (NIR), short-wavelength infrared (SWIR), and long-wavelength infrared (LWIR) sensor channels that enable the detection of oil and its byproducts, the rejection of vegetative clutter, and the discrimination of thick crude oils. The stabilized airborne payload hosting the sensors compensates aircraft roll, yaw, and forward motion – the latter using a novel, enabling forward motion compensation (FMC) technology. The airborne payload’s capabilities, combined with a ground station exploitation and human interface computer, support ocean mapping and scene interrogation, producing high-fidelity, mosaiced, geo-rectified, multi-spectral image stacks along with full motion video for use by oil spill responders.
Although advances have been made in oil spill remote detection, many electro-optic sensors do not provide real-time images, do not work well under degraded visual environments, nor provide a measure of extreme oil thickness in marine environments. A joint program now exists between BSEE and NVESD that addresses these capability gaps in remote sensing of oil spills. Laboratory experiments, calibration techniques, and field tests were performed at Fort Belvoir, Virginia; Santa Barbara, California; and the Ohmsett Test Facility in Leonardo, New Jersey. Weathered crude oils were studied spectroscopically and characterized with LWIR, and low-light-level visible/NIR, and SWIR cameras. We designed and fabricated an oil emulsion thickness calibration cell for spectroscopic analysis and ground truth, field measurements. Digital night vision cameras provided real-time, wide-dynamic-range imagery, and were able to detect and recognize oil from full sun to partial moon light. The LWIR camera provided quantitative oil analysis (identification) for >1 mm thick crude oils both day and night. Two filtered, co-registered, SWIR cameras were used to determine whether oil thickness could be measured in real time. Spectroscopic results revealed that oil emulsions vary with location and weathered state and some oils (e.g., ANS and Santa Barbara seeps) do not show the spectral rich features from archived Deep Water Horizon hyperspectral data. Multi-sensor imagery collected during the 2015 USCG Airborne Oil Spill Remote Sensing and Reporting Exercise and the design of a compact, multiband imager are discussed.
Uniform near-infrared (NIR) and short-wave infrared (SWIR) illuminators are desired in low ambient light detection, recognition, and identification of military applications. Factors that contribute to laser illumination image degradation are high frequency, coherent laser speckle and low frequency nonuniformities created by the laser or external laser cavity optics. Laser speckle analysis and beam uniformity improvements have been independently studied by numerous authors, but analysis to separate these two effects from a single measurement technique has not been published. In this study, profiles of compact, diode laser NIR and SWIR illuminators were measured and evaluated. Digital 12-bit images were recorded with a flat-field calibrated InGaAs camera with measurements at F/1.4 and F/16. Separating beam uniformity components from laser speckle was approximated by filtering the original image. The goal of this paper is to identify and quantify the beam quality variation of illumination prototypes, draw awareness to its impact on range performance modeling, and develop measurement techniques and methodologies for military, industry, and vendors of active sources.
The broadband imaging capabilities of a vanadium oxide microbolometer camera were investigated in the far-infrared for applications in real-time terahertz imaging and analysis. To accomplish this, we used an optical configuration consisting of a broadband terahertz source, terahertz filtering optics, and a modified commercial broadband microbolometer camera. A blackbody radiator was employed as the broadband terahertz source to illuminate the microbolometer array with all components in a nitrogen purged enclosure. Data was taken using several different levels of radiant flux intensity. Optical filtering were necessary to isolate incident radiation frequencies into a band from 1.5 to 7.5 THz. Fourier transform infrared spectroscopy was used to characterize the transmission properties of each optical component. The noise equivalent differential temperature (NEDT) and the noise equivalent power (NEP) were recorded over a range of blackbody intensities. We discuss the relative utility of these two figures of merit for terahertz imaging. For example, at a blackbody temperature of 925°C the NEDT was recorded below 800 mK, and the NEP was calculated to be 136 pW/√Hz. This study provides a complete analysis of a microbolometer as the detector component of a terahertz imaging system in a broadband imaging configuration.
Recent advances in the growth of rare earths doped into ceramic (poly-crystalline) materials have generated considerable interest for the next generation of tactical laser systems mainly because ceramics provide larger size, greater strength and lower cost factors in design than their single-crystalline counterparts. For many years, Nd:YAG has been the laser material choice for stability and high power Er has been an ion laser source of interest for defense due to its eye-safe emission at 1.5 μm and has applications in infrared counter-measures, illumination detection, remote sensing and communication technologies.
A model Hamiltonian including atomic and crystal-field terms is diagonalized within the complete 4f<sup>11</sup> SLJMJ basis set which includes 364 states. Within the standard deviation obtained between 117 comparable calculated-to-observed Stark levels, one set of atomic and crystal-field parameters describes the splitting of the Nd<sup>3+</sup> and Er<sup>3+</sup> energy levels in either the ceramic or single-crystal host.
We report a detailed crystal-field splitting analysis for a number of multiplet manifolds of Nd<sup>3+</sup> and Er<sup>3+</sup> in both the ceramic and single-crystal form of YAG (Y<sub>3</sub>Al<sub>5</sub>O<sub>12</sub>). With few exceptions, analysis shows that the energy-level structure of Nd<sup>3+</sup> and Er<sup>3+</sup> is similar in the ceramic and single-crystal laser rods.
The technical issues of a standoff electro-optic tripwire detector are discussed. Significant advances in short-wave infrared (SWIR) laser diodes and InGaAs detector technologies have made it possible for the demonstration of a passive and active eyesafe (1.5 micron) laser illuminated tripwire (ELIT) detector. The demonstrated system utilizes COTS laser diodes and cameras. The Hough Transform was used for the detection of tripwires in images. System trade-offs are discussed and images are shown.
Laser radar systems are required for various military applications including obstacle detection, target recognition, and terrain mapping. Each application requires different system parameters such as pulse energy, repetition rate, and field of view. This paper presents a review of a multifunction laser radar system developed and tested for the Cooperative Eyesafe Laser Radar Program (CELRAP) of the U.S. Army CECOM Night Vision and Electronic Sensors Directorate.
Laser radar systems are required for various military applications including obstacle detection, target recognition, and terrain mapping. Each application requires different system parameters such as pulse energy, repetition rate, and field of view. This paper is the second in a series of papers describing the progress toward a multifunction laser radar system under construction for the Cooperative Eyesafe Laser Radar Program (CELRAP) of the U.S. Army CECOM Night Vision and Electronic Sensors Directorate.
A 100 Hz, optical parametric oscillator (OPO) lidar breadboard is designed, built and tested for remote chemical sensing in the 8 - 12 micrometers range. Continuous tuning is achieved by angle tuning a type II, silver gallium selenide (AgGaSe<SUB>2</SUB>) OPO crystal pumped in a single step by a 2.088-micrometers pump laser. The pump source for the OPO consists of a temperature stabilized, continuously pulsed, resonantly pumped Ho:YAG (2.088-micrometers ) laser, end-pumped by a diode- end-pumped Tm:YLF (1.9-micrometers ) laser. The 9 mm X 5 mm X 25 mm-long OPO crystal was mounted on a computer-controlled galvanometer scanner for rapid wavelength tuning (1.5 micrometers between shots). Continuous tunability was demonstrated from 7.9 to 12.6 micrometers with energies in the 50 - 400 (mu) J range. Quantum slope conversion efficiencies up to 40% were obtained. Far-field beam divergence measurement showed the output of the OPO to be 2.6 times diffraction limit. The improved OPO beam quality over previous studied tandem OPO systems is attributed to the reduced Fresnel number of the OPO cavity (idler resonating) and the better beam quality of the pump source. A LabWindows based data collection and analysis system is implemented. The effectiveness of the OPO as a source for chemical sensing is demonstrated by the collection of the absorption spectrum of ammonia.
Laser radar systems are required for various military applications including obstacle detection, target recognition, and terrain mapping. Each application requires different system parameters such as pulse energy, repetition rate, and field of view. This paper presents a review of a multifunction laser radar system under construction for the Cooperative Eyesafe Laser Radar Program (CELRAP) of the U.S. Army CECOM Night Vision and Electronic Sensors Directorate.
In this paper, we review some recent advances in optical parametric oscillator (OPO) technology, discuss major coherent source issues and then propose possible solutions that have relevance to remote chemical sensing. The authors discuss their latest result on two OPO schemes. 1) Energies up to 1.2 mJ/pulse and continuously tunable OPO output from 6.7 to 9.8 micrometers was obtained using a 5 X 5 X 25 mm<SUP>3</SUP> type II AgGaS<SUB>2</SUB> crystal, pumped a second OPO using NCPM ZnGeP<SUB>2</SUB> to generate output near 8 micrometers . The tandem OPO produced pulse energies of > 1.5 mJ at 7.8 micrometers with an energy conversion efficiency of 6.8 percent. Finally, we describe schemes for generating multiple photons in the 8-12 micrometers band from one initial 1 micrometers pump photon, and thereby increase the quantum efficiency when OPOs are pumped by Nd:YAG lasers.
Advances in the development of crystals with good nonlinear properties have made optical parametric oscillators (OPOs) strong candidates for generation of coherent radiation. These technological advancements have renewed research in the development of solid state 8 - 12 micrometers coherent OPO LIDAR sources for remote chemical sensing applications, if millijoule pulse energies are adequate and short (ns) pulses are beneficial. We present recent advances in OPO technology that have generated tunable, 3 - 5 micrometers and 8 - 12 micrometers radiation. Specific pump source technologies to be addressed are CO<SUB>2</SUB>, Nd:YAG, Er and Ho:host materials. The paper will examine nonlinear materials such as ZnGeP<SUB>2</SUB>, AgGaSe<SUB>2</SUB>, AgGaS<SUB>2</SUB>, and CdSe and their relevant parameters.
Pyrromethene-BF<SUB>2</SUB> (PM) complexes doped in modified polymethyl methacrylate were evaluated and show excellent laser efficiency and damage resistance when excited at 532 nm. The spectroscopy and laser performance of a new laser dye (PM511) is discussed with emission below 550 nm. In addition, the enhanced sensitization and dual wavelength operation of dyes doped in the solid-state are demonstrated between 550 - 650 nm.
Four new BF<SUB>2</SUB>-complex laser dyes have been synthesized and spectroscopic and laser studies have been performed. The 8-cyano-pyrromethene-BF<SUB>2</SUB> complexes showed the best performance with red emission and slope efficiencies as high as 48% when pumped with a frequency doubled Nd:YAG laser. Additionally, three previously known pyrromethene-BF<SUB>2</SUB> complex dyes obtained from a commercial source were tested. These dyes showed a relative efficiency of greater than 80%, with one (PM-580) displaying a slope efficiency of 89%. This efficiency is the highest reported for any dye laser.
Pumped with two 970nm, InGaAs strained-layer diode arrays, a side-pumped Er,Yb:phospha te glass laser has been const ructed. The long pulse slope eff iciency was 14%, and threshold occurred wit h 60mJ input. The maximum output pulse energy was 20.5mJ, wit h output wavelengt hs at 1545 ± 12nm. When Q-switched, the laser prod uced 0.3mJ, 46ns FWHM pulses at an output wa velengt h of 1533 ± 1nm and wit h a repetition rate of 7Hz.
A 6.3 mm diameter by 15 mm long a-axis Nd:YLiF4 (YLF) laser rod was side-pumped by a 475 W GaAlAs diode array. A 42.9 percent optical slope efficiency was achieved while pumping in a region of low absorption in the 2H9/2, 4F5/2 band at 806 nm. Findlay-clay loss analysis and pump absorption profiles are discussed.