Pierre Simoneau

Multiresolution optical characteristics of rough sea surface in the infrared

An analytical model of sea optical properties has been developed in order to generate sea surface images, as seen by an infrared sensor. This model is based on a statistical approach and integrates the spatial variability of a wind-roughened sea surface whose variability ranges from a 1-m to a kilometer scale. It also takes into account submetric variability. A two-scale approach has been applied by superimposing small scale variability (smaller than the pixel footprint) to larger ones. Introducing multiresolution in the sensor field of view allows the requirement of any observational configuration, including nadir as well as grazing view geometry. The physical background of the methods has been tested against theoretical considerations. We also obtained a good agreement with dataset collections at our disposal and taken from the literature, such that a bias shows up at grazing angles, mainly explained by not taking into account multiple reflections. Applied to the generation of synthetic sea surface radiance images, our model leads to good quality ocean scenes, whatever the contextual conditions.

MATISSE: version 1.4 and future developments

This paper presents the MATISSE-v1.4 code whose main functionality is to compute spectral or integrated natural background radiance images. The spectral bandwidth extends from 765 to 3300 cm-1 (3 to 13 μm) with a 5 cm-1 resolution. Natural backgrounds include the atmosphere, low and high altitude clouds, sea and land. The most particular functionality of the code is to take into account atmospheric spatial variability quantities (temperatures, mixing ratio, etc) along each line of sight of the image. In addition to image generation capacity, the code computes atmospheric radiance and transmission along a line of sight with the same spectral characteristics as in imaging mode. In this case atmospheric refraction effects and radiation from high or low altitude clouds can be taken into account. A high spectral resolution mode is also available to propagate radiation from a high temperature medium in the same atmospheric state as that used for the image generation. Finally, an Application Programming Interface (API) is included to facilitate its use in conjunction with external codes. This paper describes the range of functionalities of MATISSE-v1.4 whose release is planned for April 2006. Future developments are also presented.

MATISSE-v2.0: new functionalities and comparison with MODIS satellite images

MATISSE (Advanced Modeling of the Earth for Environment and Scenes Simulation) is an infrared background scene generator developed for computing natural background spectral radiance images. The code also provides atmospheric radiatives quantities along lines of sight. Spectral bandwidth ranges from 0.4 to 14 μm. Natural backgrounds include atmosphere, sea, land and high and low altitude clouds. The new version MATISSE-v2.0, released this year, has been designed to treat spatial multi resolution in the generated images in order to be able to reach metric spatial variability in pixels footprints. Moreover, MATISSE-v2.0 includes a new sea surface radiance model (water waves and surface optical properties) which depends on wind speed, wind direction and fetch value. Preliminary validations using radiometric measurements have been conducted concerning sea radiances and give promising results. In order to go further in the validation process of MATISSE-v2.0, comparisons with MODIS satellite images have been led. The results of comparing the simulated MATISSE images radiances with the MODIS observations show that the code is performing well. This paper gives a description of MATISSE-v2.0 new functionalities and focus on first results on comparison between MATISSE/MODIS images radiances.

Infrared measurements of sea surface radiation: the MIRAMER campaign

The MIRAMER field campaign took place in the Mediterranean Sea during May 2008, both ground-based and on board an oceanographic ship. Radiometric datasets along with the associated environmental measurements have been collected in various environmental and observation conditions. It is dedicated to the validation of the sea surface optical properties model implemented in the MATISSE-v2.0 code. This analytical sea surface optical properties model in the infrared band is described. It allows the introduction of multiresolution in the simulated field-of-view answering the need in computed images including any observational configurations. It is valid for fully-developed seas, includes shadowing and hiding functions but not breaking and foam nor multiple reflections. First comparisons between simulations and measurements are presented in this paper.

MATISSE-v1.5 and MATISSE-v2.0: new developments and comparison with MIRAMER measurements

MATISSE is a background scene generator developed for the computation of natural background spectral radiance images and useful atmospheric radiatives quantities (radiance and transmission along a line of sight, local illumination, solar irradiance ...). The spectral bandwidth ranges from 0.4 to 14 μm. Natural backgrounds include atmosphere (taking into account spatial variability), low and high altitude clouds, sea and land. The current version MATISSE-v1.5 can be run on SUN and IBM workstations as well as on PC under Windows and Linux environment. An IHM developed under Java environment is also implemented. MATISSE-v2.0 recovers all the MATISSE-v1.5 functionalities, and includes a new sea surface radiance model depending on wind speed, wind direction and the fetch value. The release of this new version in planned for April 2009. This paper gives a description of MATISSE-v1.5 and MATISSE-v2.0 and shows preliminary comparison results between generated images and measured images during the MIRAMER campaign, which hold in May 2008 in the Mediterranean Sea.

Radiative transfer model in a cloudy atmosphere: a comparison with airborne cumulus measurement

A new model of radiative transfer in a cloudy atmosphere NUALUM has been developed at ONERA. NUALUM uses the Discrete Ordinates Method. This code includes multiple scattering in clouds and takes into account the azimuthal distribution of radiation. NUALUM allows geometry and microphysics of the cloud to be varied (particle size, concentration, top and bottom altitude). The parameterization of a cumulus cloud with NUALUM is compared with airborne measurements performed by ONERA and CELAR: circularvariable filter cryogenic spectrometer SICAP (1.5-5.5 j.tm) and airborne infrared camera CIRAP (3-5 pm and 8-12 tm) aim at the same point of the cloud top. The observation azimuthal angle is variable. SICAP spectral measurements show great variations of the radiation with the azimuthal angle which are in agreement with NUALUM simulations. The correlation between the infrared radiation images CIRAP and mean calculated radiation is satisfactory.

Multiresolution optical properties of rough sea surface in infrared

The purpose of this paper is to take into account the spatial variability of a wind-roughened sea surface from 1-meter to large scale including sub-metric variability. An analytical model of infrared sea surface optical properties based on a statistical approach is proposed. We introduce a new two-scale model consisting in superimposing the small scale variability (smaller than the pixel footprint) to the large scale one. The analytical expressions given in literature are extended to account for any slope mean vector-value and covariance matrix, and the statistical properties are determined for the resolution required by the observational configuration. Verifications of the physical validity of this new approach are presented. They globally show a good agreement. A bias is observed at grazing angles, mainly explained by the fact that the multiple reflections are ignored. Our model has also been implemented for the generation of synthetic sea surface radiance images, showing its ability to produce good quality ocean scenes in various contextual conditions.

Infrared multiscale sea surface modeling

An analytical model of infrared sea surface optical properties is developed to access to statistical radiative characteristics of a wind-roughened water surface. Any surface size, i.e. that contains or not all the statistical information of the stochastic process governing the sea surface, can be considered. This model deals with the problem of multi-resolution in a sensor field of view. Model validation has been conducted in 1D by comparison with a reference code and in 2D by comparisons with optical properties measurements and with validated 1D cross sections.

Airborne stratus measurement and comparison with NUALUM code

Airborne measurement of stratus is being carried out by ONERA in order to validate NUALUM cloud simulation. The cloud top is measured by a circular variable filter cryogenic spectrometer SICAP. Two observation zenith angles are tested and the azimuth angle is variable. In situ liquid water content (LWC) measurement in performed by a Johnson Williams probe and compared with meteorological sounding. The liquid water content has been valuated inside a layer from 200m to 600m altitude. Mean LWC is equal to 0.3g/m3. Those values are typical of a stratus. The NUALUM cloud radiative transfer code has been developed at ONERA. The optical properties are computed by MIE theory. NUALUM includes the DISORT code to compute the multiple scattering in the cloud, by the mean of the discrete ordinates method. Spectral measurements show great variations of the radiation according to the azimuth angle when the wavelength is less than 4 micrometers . In this range of wavelength, radiation provides from solar reflection which is very sensitive to the scattering angle. Above 4 micrometers , thermal radiance increases. A good correlation is observed between the shape of the phase function of cloud particles and the radiance variation with scattering angle. NUALUM is in agreement with the stratus spectral measurements. During the experiment, sea spectral measurements have also been carried out. Solar reflection on the sea surface of the sea is specular and only occurs for low scattering angles.

Nightglow studies at Onera for night-vision applications

Since 2010 Onera works on the characterization of the nightglow radiation for night-vision applications in moonless conditions. This radiation is mainly due to the deexcitation of hydroxyl molecules in the upper atmosphere (~87km). It is present in the visible range and reaches its maximum value in the short wavelength infrared bands between 1.4 and 1.8μm (Meinel bands). Although few energy reaches the ground, this radiation is emitted over the whole sky and therefore may be an interesting additional light source for night vision systems in moonless or cloudy sky conditions. Moreover, observation of the nocturnal sky in the short wave infrared band gives access to dynamic processes studies, these processes perturbing emission of radiation. In this paper, we present works carried out at Onera about observation and modelling of nightglow radiation.