Target Surface Material Research Articles

Influence of Target Surface BRDF on Non-Line-of-Sight Imaging

The surface material of an object is a key factor that affects non-line-of-sight (NLOS) imaging. In this paper, we introduce the bidirectional reflectance distribution function (BRDF) into NLOS imaging to study how the target surface material influences the quality of NLOS images. First, the BRDF of two surface materials (aluminized insulation material and white paint board) was modeled using deep neural networks and compared with a five-parameter empirical model to validate the method’s accuracy. The method was then applied to fit BRDF data for different common materials. Finally, NLOS target simulations with varying surface materials were reconstructed using the confocal diffusion tomography algorithm. The reconstructed NLOS images were classified via a convolutional neural network to assess how different surface materials impacted imaging quality. The results show that image clarity improves when decreasing the specular reflection and increasing the diffuse reflection, with the best results obtained for surfaces exhibiting a high diffuse reflection and no specular reflection.

A Calculation Method for the Hyperspectral Imaging of Targets Utilizing a Ray-Tracing Algorithm

This paper proposes a hyperspectral imaging simulation method based on a ray-tracing algorithm. The algorithm combines calculations based on solar and atmospheric visible light radiation as well as the spectral bidirectional reflection distribution function (BRDF) of the target surface material and can create its own scenarios for simulation calculations on demand. Considering the presence of multiple scattering between the target and background, using the ray-tracing algorithm enables the precise computation of results involving multiple scattering. To validate the accuracy of the algorithm, we compared the simulated results with the theoretical values of the visible light scattering intensity from a Lambertian sphere. The relative error obtained was 0.8%. Subsequently, a complex scene of engineering vehicles and grass was established. The results of different observation angles and different coating materials were calculated and analyzed. In summary, the algorithm presented in this paper has the following advantages. Firstly, it is applicable to geometric models composed of any triangular mesh elements and accurately computes the effects of multiple scattering. Secondly, the algorithm combines the spectral BRDF information of materials and improves the efficiency of multiple scattering calculations using nonuniform sampling. The computed hyperspectral scattering data can be applied to simulate airborne or space-borne remote sensing data.

Effects of Hugoniot properties on jet onset conditions

Jets are the earliest ejected material from a hypervelocity impact event. Jets comprises of projectile and target's surface material and are ejected at velocities higher than escape velocity for Earth. Effects of Hugoniot properties of the projectile and target material on jet initiation are not well understood. We, therefore, developed a mathematical model that incorporated the limitations imposed by Hugoniot properties on jet initiation for hypervelocity impact. This model analysed the effects of changes in Hugoniot properties of the projectile and target on the jet onset time, jet onset velocity and jetting side (projectile or target). The results reveal that (i) jet initiates earlier and at higher velocity if the jetting side has higher value of shock parameter or higher velocity of sound in the material; (ii) jet initiates later and at lower velocity if jetting side has high density; (iii) effect of s-parameter and speed of sound in material is more profound than the effect of density.

Assessment of ITER divertor performance during early operation phases

During the ITER design phase, the focus of ITER boundary plasma modeling activities has been on divertor performance under baseline H-mode, fusion power operation (FPO) conditions. However, early ITER operation will be primarily with hydrogen fuel in L-mode, in the pre-fusion power operation 1 (PFPO-1) phase. Here, the SOLPS-ITER code is used to evaluate divertor performance during this non-active phase. To verify the assumptions used in the existing high power simulation database, gas throughput scans were performed for two types of divertor surface material (beryllium and tungsten) and two gas puff locations (divertor and main chamber). The adoption of beryllium target surfaces simulates the effect of main chamber material erosion and migration and, along with main chamber gas injection, is the current default for the high power database. Depending on the divertor surface material, the atom to molecule ratio of the recycled neutral particles varies. This modifies the momentum and power loss mechanisms arising from plasma–neutral interactions. However, since the effect of atomic and molecular reactions are compensatory, the ‘total’ power and momentum losses are relatively insensitive to the target surface material. Similarly, the impact of gas puff location on divertor plasma parameters is not significant, though main chamber injection provides an additional ionization source in the upstream scrape-off layer (SOL) and leads to moderate changes in the upstream density and far SOL parameters. However, these effects can be neglected within the available range of the gas puff and pump rates in ITER. Since beryllium and tungsten are materials at both extremes in terms of surface reflection properties, the conclusions may be applicable to other divertor surface materials. An important additional finding of the study is that the insensitivity of upstream density to divertor neutral pressure found in the FPO database is also recovered in these PFPO-1 simulations.

A practical method for employing multi-spectral LiDAR intensities in points cloud classification

ABSTRACT Light Detection and Ranging (LiDAR) intensity is associated with the target surface material, which could help the points cloud classification. However, the intensity is also associated with the laser beam incident angle and the transmitting distance, which obstructs its further application in points cloud classification. Motivated by this problem, this paper proposed a practical method for employing the LiDAR intensities in points cloud classification without distance and incident angle calibration, specifically, ratio values between different spectral channels from a newly invented Hyper-spectral LiDAR (HSL) were defined and calculated for generating robust spectral features. Since the HSL different channels had the same transmitting distance and incident angle, therefore, the ratio values were independent on the laser pulse transmitting distance and laser beam incident angle. An indoor experiment was conducted for fully assessing the proposed method. The HSL had eight different spectral channels with spectral wavelength covering from 650 nm to 1000 nm. In the experiments, papers with different colours were pasted on a flat glass; the HSL scanned them at four distinctive positions with 60 cm displacement. The spectral ratio values between different channels at each position were calculated using the obtained multiple spectral profiles from the HSL. The results showed that the points cloud scanned at different incident and distance could be classified though the spectral ratio values without complex distance and incident angle calibration.

Emission spectra of a simulated Chicxulub impact-vapor plume at the Cretaceous–Paleogene boundary

A plume of vaporized sediments and basement rocks was ejected to the top of atmosphere when a 10–15 km asteroid impacted on Yucatan in the Southern Gulf of Mexico about 66 million years ago. The Chicxulub impact-vapor plume emitted a flash of light that had clues on the chemistry and degree of vaporization of the target surface material. Here we simulate the asteroid impact by vaporizing marine carbonate sediments cored in the Yaxcopoil-1 borehole in the Chicxulub crater using an intense infrared laser pulse. We investigate two sedimentary layers that represent the most dominant mineral phases of the target sequence: carbonates and sulfates. Their main constituents are 86% calcite and 74% anhydrite, respectively. The laser-induced vapor plumes were produced from each layer in a background simulated late Cretaceus atmosphere (0.16% CO2, 30% O2, and 69.84% N2). Time-resolved spectroscopic analyses from the laser-induced plumes were carried out using experimental and synthetic spectra. The vapor plumes had similar temperatures (≥7800 K) at 1 μs and their spectra showed similar emissions. The spectra contained the following lines in nm: Ca+ (mostly at 393.4 and 396.9 with less prominence at 370.6 and 373.7), Ca (422.7, 430.3, 443.6, 445.5, 527.0, 560.3, 616.4, and 657.3), N (746.8 and 821.6), O (777.7), and C (794.5). Molecular bands were not conspicuous which indicated complete vaporization of the target material by the laser pulse. The contribution of the granitic basement was examined using synthetic spectra. The expected emissions according to their intensities are: Na (589.6), Ca+ (393.4), Al (396.2, 309.3), Ca+ (396.9), Ca (422.7), Na (819.5) and K (766.5, 769.9). The results suggest that the emission corresponded to Ca+ and Ca originated mostly from the volatilization of the marine sediments, and Na, Al, and K from the basement rocks. The physico-chemical evolution of the Chicxulub impact-vapor plume could be deduced by deciphering the temperature and electron density from the emission lines of Ca and Ca+. These physical parameters can be used in gas dynamic models to predict the fluxes and nature of gases, vapors and mineral phases that were introduced into the atmosphere and better assess their impact to the environment and the biosphere.

Range Information Characterization of the Hokuyo UST-20LX LIDAR Sensor

This paper presents a study on the data measurements that the Hokuyo UST-20LX Laser Rangefinder produces, which compiles into an overall characterization of the LiDAR sensor relative to indoor environments. The range measurements, beam divergence, angular resolution, error effect due to some common painted and wooden surfaces, and the error due to target surface orientation are analyzed. It was shown that using a statistical average of sensor measurements provides a more accurate range measurement. It was also shown that the major source of errors for the Hokuyo UST-20LX sensor was caused by something that will be referred to as “mixed pixels”. Additional error sources are target surface material, and the range relative to the sensor. The purpose of this paper was twofold: (1) to describe a series of tests that can be performed to characterize various aspects of a LIDAR system from a user perspective, and (2) present a detailed characterization of the commonly-used Hokuyo UST-20LX LIDAR sensor.

The design and implementation of photoacoustic based laser warning receiver for harsh environments

This paper discusses the implementation of new type of laser warning receiver (LWR) system, based on the detection of photoacoustic signals, induced by high power infrared laser designators pulses on target’s surfaces. This system appends conventional optoelectronic based LWR to decrease the false alarm rate (FAR) in harsh environments, where ambient conditions are expected to obstruct optical LWR. To improve the sensitivity of the photoacoustic based LWR system, some metallic and polymeric target shielding materials were studied, in order to cover a friendly civil structure, vehicle or a maritime entity with a low cost large area acoustic detector array shield. A thermographic investigation of target surface material- laser reaction, signal processing and system configuration and functional analysis are also presented.

Identification of amino acids by material enhanced laser desorption/ionisation mass spectrometry (MELDI-MS) in positive- and negative-ion mode

In the present study, different silica gel modifications were evaluated for their application as target surface for material enhanced laser desorption/ionisation mass spectrometric (MELDI-MS) investigation of amino acids. 4,4′-Azodianiline (ADA-silica) modified silica gel was successfully employed for the qualitative analysis of amino acids in positive- and in negative-ion mode. Further no derivatisation of amino acids was necessary, as the introduced system allowed the direct analysis of targets and delivered spectra with excellent signal intensity and signal-to-noise ratio within a few minutes. The influence of surface chemistry, ionisation mode and the nature of analytes on signal intensity was studied and discussed. Detection limit of 2.10 pg (10 fmol) was achieved by employing ADA-silica in positive-ion mode. Finally, xylem saps from different types of trees were analysed. This proved the high performance and excellent behaviour of the introduced target surface material.

Effect of laser intensity on the properties of carbon plasmas and deposited films

The effect of laser intensity on the deposition of diamondlike carbon (DLC) films has been studied using an ArF (193 nm) pulsed excimer laser. Our results are found to be distinct from other studies using Nd-YAG infrared or excimer 248-nm lasers. Two issues concerning the growth mechanism of the films are discussed: (1) the dynamics of the laser-induced plasma and (2) the dependence of the nature of the deposited films on laser intensity. To address the first issue, time-integrated optical emission spectroscopy has been carried out to investigate the carbon plasma induced by the ArF (193 nm) laser. Instead of molecular carbon bands (C{sub 2}), monoatomic neutral (C{sub I}) and ionic (C{sub II}) emission lines are found to dominate the spectra. The emissions of (C{sub I}) and (C{sub II}) have been studied as a function of laser intensity. For low laser intensity, the laser irradiation removes the target surface material primarily through thermal evaporation. When the laser intensity is above a threshold of (3.7{endash}4){times}10{sup 8} W/cm{sup 2}, the evaporated species are also ionized. The observed phenomenon can be attributed to higher multiphoton ionization and inverse bremsstrahlung rate as the laser intensity is increased. For the second issue, films deposited atmore » various intensities have been characterized by ellipsometry. Results show that films deposited at low intensity are found to have excellent optical transparency (E{sub g}=2.3 eV), which implies a considerable amount of sp{sup 3} bonds. However, films deposited at higher intensities are found to be more graphitic. The damage threshold has also been located at 3.7{times}10{sup 8} W/cm{sup 2}. A qualitative structural analysis based on the effective-medium approximation has been performed on the deposited films to investigate the influence of laser intensity on their microstructures. {copyright} {ital 1997} {ital The American Physical Society}« less

Divertor Engineering for the ARIES-I Reactor†

The ARIES tokamak-reactor design study is a multi-institutional project investigating several different visions of the tokamak as a commercial power reactor. The ARIES-I reactor design incorporates modest extrapolation of existing physics with advanced technology in the fusion power core (FPC) design. Use of aggressive technology such as high-field magnets and low-activation silicon-carbide (SiC) composites help to make ARIES-I an attractive reactor with excellent safety characteristics. The ARIES-I reactor uses a double-null poloidal-field (PF) divertor for particle exhaust and impurity control. Control of the edge-plasma density and temperatures has reduced the energy of the incident particles at the divertor to ∼20 eV, which is below the self-sputtering threshold for the tungsten target surface material. The target is constructed of SiC composite tubes with a 2-mm-thick plasma-sprayed coating of tungsten on the plasma-facing side and a 0.5-mm chemical-vapor deposited (CVD) coating of SiC on the back. The divertor is cooled by helium at lOMPa with inlet/outlet temperatures of 350°/650°C. In removing the divertor surface heat flux of 4.5 MW/m2, a design safety factor of 1.8 is achieved. The divertor has a waste disposal rating of 0.10 (see text for definition), thus allowing Class-C shallow land burial, and a site boundary dose of 11.2 rem during an accidental release. Isotopic tailoring of the tungsten and target replacement every two years is necessary to achieve these safety characteristics.

Search for shell disintegration in laser implosion experiments

The possibility of shell disintegration in thin-wall targets as indicated by mixing of target surface material into the compressing core in laser-induced implosions has been investigated. Aluminum coated glass microballoon targets were irradiated by a two-beam Nd:phosphate glass laser with laser power up to 250 GW on target. The occurrence of mixing in these exploding pusher implosions was determined by using spatially resolved x-ray spectroscopy. Mixing was not observed except for laser shots with an intentional prepulse (∼10 mJ, 1.5 nsec before the main pulse).

Statistics of the laser radar cross section of a randomly rough target*

The problem of calculating the laser radar cross section of a randomly rough target is studied. It is shown that subject to a minimum set of assumptions, all with reasonable physical interpretation, the statistics are Rician for any degree of roughness. A rigorous theory is developed to allow the two parameters of the Rician distribution to be calculated for any target shape, using only a small set of laboratory measurements of laser scattering from two simply shaped samples of the target surface material. It is noted that it is never necessary to become involved in measurements of the statistics of the target’s microscopic roughness or in the problem of electromagnetic boundary matching conditions in order to calculate the laser radar cross section of a large complex shaped target.