Romain Ceolato

• PhD
• Researcher at ONERA - University of Toulouse

The modeling of radiative properties of soot particles can be addressed by a number of methods. Among them, the canonical Rayleigh-Debye-Gans (RDG) theory and the Superposition T-Matrix Method (STMM) are particularly well adapted to the task. Here, both RDG and STMM are used to model the radiative properties of two types of fractal aggregates indic...

A bi-static short-range elastic backscatter micro-lidar, named Colibri, has been developed for quantitative aerosol profiling with high range and temporal resolution within the first hundred meters. The geometric (i.e., overlap) and radiometric (i.e., lidar constant) calibrations were performed along with dark current and background noise character...

Elastic backscatter lidar is an established method useful to characterize the particles forming an atmospheric aerosol. Fundamental to lidar measurements are the extinction and backscattering properties of the aerosol particles in the lidar beam. This review aims to give the reader an understanding for how lidar measurements are made, modeled, and...

Using a supercontinuum laser, reflective optics, and a spatial filter, we measure two-dimensional small-angle light-scattering patterns for a variety of microparticles including spheres, salt, sand, and volcanic dust. The measurements are done at 13 wavelengths from 450–850 nm, where the absence of refractive optical elements minimizes the effects...

Black carbon aerosol emissions are recognized as contributors to global warming and air pollution. There remains, however, a lack of techniques to remotely measure black carbon aerosol particles with high range and time resolution. This article presents a direct and contact-free remote technique to estimate the black carbon aerosol number and mass...

A method is developed to isolate the interference-fringe pattern associated with an individual particle from a single digital in-line hologram containing overlapping patterns from multiple particles. The method is illustrated with a measured hologram of road-dust aerosol particles nominally 20-50 µm in size. It is further tested for 2.5-3.0 µm part...

Plain Language Summary Dust particles suspended in air are important for the radiative energy budget of Mars. By interacting with solar radiation, these aerosols impact the temperature, dynamics, and composition of the atmosphere, as well as the surface temperature of Mars. Dust aerosols are produced by wind‐lifting processes ranging from small‐sca...

The hyperspectral component of bidirectional reflectance measurements, namely from several hundred wavelengths upwards, is attracting growing interest for numerous applications in both optics and computer graphics. In this paper, we present a motorized hyperspectral bidirectional reflectance measurement bench that performs in-plane and out-of-plane...

Short-range elastic backscatter lidar (SR-EBL) systems are remote sensing instruments for studying low atmospheric boundary layer processes. This work presents a field campaign oriented to filling the gap between the near-surface aerosol processes regarding aerosol radiative properties and connecting them with the atmospheric boundary layer (ABL),...

The optical extinction caused by a small particle, such as an aerosol particle, is an important measurable quantity. Understanding the influence of atmospheric aerosols on the climate, assessing visibility in urban environments, and remote sensing applications such as lidar all need accurate measurements of particle extinction. While multiple metho...

A novel Short-Range High Spectral Resolution Lidar (SR-HSRL) instrument is presented using a non-injection seeded diode-based laser emitting low energy pulses at a high repetition rate and an iodine cell for spectral filtering. This instrument is used as a proof-of-concept to measure separately the aerosol Mie and molecular Rayleigh backscatter sig...

Digital in-line holography is a versatile method to obtain lens-less images of small particles, such as aerosol particles, ranging from several to over one hundred microns in size. It has been shown theoretically, and verified by measurement, that a particle’s extinction cross section can also be obtained from a digital hologram. The process involv...

The aim of this paper is to present a novel lidar technique, based on supercontinuum laser sources, for aerosol remote sensing. Precisely, we show the feasibility of such supercontinuum lidar aerosols measurements. For that, a novel simulator of the supercontinuum lidar is proposed, as complete as possible, that takes into account different charact...

This study presents a synergistic approach to the study of the aerosol optical and microphysical properties measured in La Palma, Spain, during the 2021 eruption of the Cumbre Vieja volcano (from 19 September to 13 December 2021). This study aims to characterize the different phases of the volcanic eruption using the spatio-temporal evolution of th...

The Rayleigh-Debye-Gans approximation for fractal aggregates (RDG-FA) is commonly used to evaluate the radiative properties of soot aerosols composed of nano-spheres due to its analytical character. Despite neglecting electromagnetic coupling within an aggregate, the RDG-FA provides a simple interpretation of angular light-scattering measurements i...

The Rayleigh Debye-Gans approximation for Fractal Aggregates (RDG-FA) is commonly used for the evaluation of the radiative properties of fractal aggregates of nanometer-scale nearly spherical particles as soot particles. The cost of its simplicity, however, is the precision of the aggregate cross sections when the refractive index deviates from uni...

Black carbon aerosol emissions are recognized as contributors to global warming and air pollution. There remains, however, a lack of in-situ techniques to remotely quantify black carbon aerosol particles with high range and time resolution. This article presents for the first time, to our knowledge, a direct and contact-free remote measurement of b...

The solution of the lidar equation is an ill-posed problem that requires nonlinear methods to retrieve the atmospheric aerosol optical and microphysical properties. Particularly, in the last decades, the most applied solution for the elastic lidars is through the well known Klett-Fernald-Sasano algorithm for retrieving the backscatter coefficient....

Rayleigh-Debye-Gans (RDG) theory is a commonly used approximation for light scattering and absorption by nanoparticles in the visible spectrum. The aim of this study is to advance our understanding for the origin of empirically observed deviations between accurate calculations of forward scattering and the absorption cross-sections and those predic...

In this paper, a controlled-laboratory experiment is carried out to evaluate the lidar depolarization ratio of freshly emitted soot aggregates in the exact backward scattering direction at 180.0°. The experiment is performed at two wavelengths simultaneously, namely 355 and 532 nm, often used in polarimetric lidar remote sensing. The soot aggregate...

We examine the capability of near-spherical-shaped particles to reproduce the triple-wavelength particle linear depolarization ratio (PLDR) and lidar ratio (LR) values measured over Europe for stratospheric smoke originating from Canadian wildfires. The smoke layers were detected both in the troposphere and the stratosphere, though in the latter ca...

Recent ceilometer models are more sensitive to aerosols, which is increasing the interest in these instruments to retrieve aerosol optical and microphysical properties. In this paper, a new methodology is proposed to retrieve aerosol vertical extinction and backscatter profiles from a Vaisala ceilometer CL51 model. This methodology is based in two...

Infrared Stealth is an important aspect in the design and performance assessment of the future combat aircraft. In this paper, we propose a statistical approach based on an aircraft signature code to assess the impact of different technology choices. As simulations can be computationally demanding, we set-up and validate a multifidelity surrogate m...

An experiment is described where two-dimensional small-angle light scattering (2D-SALS) patterns from single particles are measured in the infrared through a lens-free approach. Spatial filtering is employed to separate scattered light from unscattered light to within approximately one degree from the forward direction. Non-planar reflective elemen...

We present smoke lidar measurements from the Canadian fires of 2017. The advected smoke layers over Europe are detected at both tropospheric and stratospheric heights, with the latter presenting non-typical values of the Particle Linear Depolarization Ratio (PLDR) with strong wavelength dependence from the UV to the Near-IR. Specifically, the PLDR...

In this paper, a new elastic lidar inversion equation is presented. It is based on the backscattering signal from a surface reference target (SRT) rather than that from a volumetric layer of reference (Rayleigh molecular scatterer) as is usually done. The method presented can be used when the optical properties of such a layer are not available, e....

In this paper, a new elastic lidar inversion equation is presented. It is based on the backscattering signal from a surface reference target (SRT) rather than that from a volumetric layer of reference (Rayleigh molecular scatterer) as usually done. The method presented can be used when the optical properties of such a layer are not available, e.g....

This study presents the averaged lidar-relevant radiative properties of numerically generated soot fractal aggregate ensembles. The radiative properties of these aggregates have been computed using the Superposition T-Matrix Method, with emphasis put on those that are most relevant to lidar application; the backscattering and extinction cross-secti...

The aim of this work is to present the recent advances in high spatial resolution profiling of aerosols with a short-range multi-static elastic lidar system. Our results demonstrate the feasibility of robust lidar measurements of smoke plumes in the short-range with high spatial (<50 cm) resolution in order to retrieve the optical and microphysical...

Lidar measurements of smoke from two different events of large scale fires, revealing non typical values of the Particle Linear Depolarization Ratio (PLDR), are presented. The aged, elevated smoke layers in the stratosphere were observed with the portable polarization, Raman lidar Polly XT of the National Observatory of Athens (NOA), based at Finok...

We present lidar measurements of aged tropospheric and stratospheric smoke plumes, originating from the large scale Canadian fires in August 2017. Retrieval of the optical properties showed that for the stratospheric layer the values of Particle Linear Depolarization Ratio (PLDR) deviate from typical ones at both measurement wavelengths, while this...

The global warming and environmental issues imply the study of anthropogenic airborne particulate matter (PM), such as carbonaceous or soot aerosols, emitted by several sources. Carbona-ceous particulate matter emitted by aircraft engines is due to incomplete fuel combustion. These particles can have long residence times in the upper troposphere an...

Spectro-polarimetric light-scattering, or merging spectral and polarimetric light-scattering information, is a growing interest in a wide range of scientific fields. Recently, it has been demonstrated how spectral polarimetric light-scattering could be employed to probe microphysical properties of particulate media, for instance mean particle size...

This work assesses the ability of equivalent-sphere models to reproduce the optical properties of soot aggregates relevant for lidar remote sensing, i.e. the backscattering and extinction cross sections. Lidar cross-sections are computed with a spectral discrete dipole approximation model over the visible-to-infrared (400–5000 nm) spectrum and comp...

Spectralons are reference radiometric samples which exhibit a calibrated reflectance. However, in case of low reflectance samples, the degree of polarization (DOP) of scattered light is hard to characterize. Here, an accurate determination of spectralon spatial depolarization is proposed. Based on a spatially resolved polarimetric imaging system, t...

Tissue mimics (TMs) on the scale of several hundred microns provide a beneficial cell culture configuration for in vitro engineered tissue and are currently under the spotlight in tissue engineering and regenerative medicine. Due to the cell density and size, TMs are fairly inaccessible to optical observation and imaging within these samples remain...

This paper addresses the problem of critical operations in Degraded Visual Environment (DVE). DVE usually refer when the perception of a pilot is degraded by environmental factors, including the presence of obscurants from bad weather (e.g. fog, rain, snow) or accidental events (e.g. brownout, whiteout, smoke). Critical operations in DVE are a grow...

Spectral polarimetric light-scattering by particulate media has recently attracted growing interests for various applications due to the production of directional broadband light sources. Here the spectral polarimetric light-scattering signatures of particulate media are simulated using a numerical model based on the spectral Vector Radiative Trans...

A non-invasive optical technique, based on a supercontinuum laser source and hyperspectral sensors, is established to measure the spectral degree of linear polarization (DOLP) in a broad spectral range from 525 nm to 1000 nm. Several biomaterials of interest, such as healthy and cancerous skins, are considered. The spectral DOLP of melanoma, from 5...

The goal of this paper is to present an in-vitro label-free technique based on light-scattering to study optical properties of MultiCellular Tumor Spheroids (MCTS). Our non-imaging technique provides a complete optical signature from hyperspectral polarimetric and angular light-scattering measurements using a coherent white-light supercontinuum las...

Onera, the French aerospace lab, develops and models active imaging systems to understand the relevant physical phenomena affecting these systems performance. As a consequence, efforts have been done on the propagation of a pulse through the atmosphere and on target geometries and surface properties. These imaging systems must operate at night in a...

Our work presents computations via a vectorial radiative transfer model of the polarimetric and angular light scattered by a stratified dense medium with small and intermediate optical thickness. We report the validation of this model using analytical results and different computational methods like stochastic algorithms. Moreover, we check the mod...

This work applies a new model based on the discrete dipole approximation to simulate the scattering of coherent broadband light from fixed and randomly oriented silica fractal aggregates. Two classes of aggregate morphology are considered; the standard aggregate with a single fractal dimension and superaggregates with two dimensions, both of which...

One of the key technologies in future optoelectronics is control of excitons in oxide materials by the coupling with plasmons on noble metal surfaces. Optical properties of ZnO nanowires decorated with Au nanoparticles were studied to understand fundamental mechanism of the coupling and to develop optoelectronic devices with new functionalities. Li...

Electromagnetic scattering occurs by the presence of discontinuities or scatterers. Ensemble of particles often form clusters or aggregates of particles. Most scattering models assume that such complex ensemble are placed in non-absorbing media. However, for many applications, absorption of the host media cannot be neglected for particular frequenc...

Recent developments of active hyperspectral systems require optical characterization of man-made materials for instrument calibration. This work presents an original supercontinuum laser-based instrument designed by Onera, The French Aerospace Lab, for fast hyperspectral polarimetric and angular reflectances measurements. The spectral range is from...

Onera, the French Aerospace Lab, develops and models 2D and 3D active imaging systems to understand the relevant physical phenomena impacting on their performances. As a consequence, efforts have been done both on the propagation of a pulse through the atmosphere (scintillation and turbulence effects) and, on target geometries and their surface pro...

Control and characterization of nanomaterial synthesis have been a great challenge for years. Onera, The French Aerospace Lab, has developed a fast, in-line and comprehensive characterization method based on the combination of hyperspectral, polarized and angular measurements. In this paper, physical and optical properties are measured to control a...

Supercontinuum laser sources provide a very useful tool to characterize materials and scattering media such as nanomaterials in suspensions, aerosols or paint coatings. Onera, The French Aerospace Lab, has developed a fast, in-line and comprehensive optical characterization method. The hyperspectral polarized angular light measurements by tumor cel...

The spectral BRDF of various common urban materials has been measured for the purposes of facilitating the further development of remote sensing in urban scenes. It is seen that the usual assumption of lambertian surfaces only hold for highly rough surfaces. For smooth manmade materials, the point of specularity not only has a higher magnitude, but...

Recent innovations in Supercontinuum or white laser sources provide a very useful tool to probe nanomaterials physical and optical properties. Onera, The French Aerospace Lab, has developed a fast, in-line and comprehensive optical characterization method. From the combination of hyperspectral, polarized and angular measurements, physical propertie...

Multispectral and polarized light reflectance measurements are very useful to characterize materials such as paint coatings. This article presents an overview of an automated high-angular resolved, in-plane multispectral polarized reflectometer and its calibration process. A compre-hensive study based on multispectral BRDF and DOLP measurements is...

Using laser imaging systems to represent 3-D scene becomes a referent prospective technology in the areas of guidance and navigation. Measurements with high spatial resolution for significant range can be achieved, even in degraded visibility conditions such as the Brown-White Out, rain, fog, sandstorms... Moreover, this technology is well suited f...

Using laser imaging systems to represent 3-D scene becomes a referent prospective technology in the areas of guidance and navigation. Measurements with high spatial resolution for significant range can be achieved, even in degraded visibility conditions such as the Brown-White Out, rain, fog, sandstorms... Moreover, this technology is well suited f...

Onera, the French Aerospace Lab, develops and models active imaging systems to understand the relevant physical phenomena impacting on their performances. As a consequence, efforts have been done both on the propagation of a pulse through the atmosphere (scintillation and turbulence effects) and, on target geometries and their surface properties (r...

Recent developments of active imaging and remote sensing systems in security and defence community require comprehensive optical characterizations of man-made targets. Optical signature analysis of various targets implies a better and comprehensive understanding of reflectance properties such as Bidirectional Reflectance Distribution Function (BRDF...