Bidirectional Reflectance Distribution Function Value Research Articles

Multi-spectral bidirectional reflectance characteristics of crude oils

Bidirectional reflectance distribution function (BRDF) has important and extensive applications in remote sensing. The polarized light field is certainly promising for it has the capacity of transmitting more information. In this study, total and polarized BRDF in visible and near-infrared bands of three crudes and pure water were measured through a self-designed scatterometer. The spectral and angle profile properties of BRDF were analyzed. The results indicate that it is achievable to detect crude from the background of water and identify oil types via characteristics of BRDF. The BRDF of the four liquids is in connection with its components. The value of BRDF of the Daqing crudes is significantly higher than that of water for the energy consumption efficiency of water molecules is higher than oil. In contrast, the high content of asphalt of Gudao crude result in it has a lower BRDF value and exhibits a slighter diffuse reflection characteristic. Furthermore, a relative contrast was adopted to assess the detectability of oil, and the conditions when relative contrast to maximum was given. The polarized parameters exhibit its advantage in oil detection with greater relative contrast and reflected intensity at optimal observation conditions.

Suomi NPP VIIRS solar diffuser screen transmittance model and its applications.

The visible infrared imaging radiometer suite on the Suomi National Polar-orbiting Partnership satellite calibrates its reflective solar bands through observations of a sunlit solar diffuser (SD) panel. Sunlight passes through a perforated plate, referred to as the SD screen, before reaching the SD. It is critical to know whether the SD screen transmittance measured prelaunch is accurate. Several factors such as misalignments of the SD panel and the measurement apparatus could lead to errors in the measured transmittance and thus adversely impact on-orbit calibration quality through the SD. We develop a mathematical model to describe the transmittance as a function of the angles that incident light makes with the SD screen, and apply the model to fit the prelaunch measured transmittance. The results reveal that the model does not reproduce the measured transmittance unless the size of the apertures in the SD screen is quite different from the design value. We attribute the difference to the orientation alignment errors for the SD panel and the measurement apparatus. We model the alignment errors and apply our transmittance model to fit the prelaunch transmittance to retrieve the "true" transmittance. To use this model correctly, we also examine the finite source size effect on the transmittance. Furthermore, we compare the product of the retrieved "true" transmittance and the prelaunch SD bidirectional reflectance distribution function (BRDF) value to the value derived from on-orbit data to determine whether the prelaunch SD BRDF value is relatively accurate. The model is significant in that it can evaluate whether the SD screen transmittance measured prelaunch is accurate and help retrieve the true transmittance from the transmittance with measurement errors, consequently resulting in a more accurate sensor data product by the same amount.

Numerical reproduction and explanation of road surface mirages under grazing-angle scattering.

The mirror-like reflection image of the road surface under grazing-angle scattering can be easily observed in daily life. It was suggested that road surface mirages may occur due to a light-enhancing effect of the rough surface under grazing-angle scattering. The main purpose of this work is to explain the light-enhancing mechanism of rough surfaces under grazing-angle scattering. The off-specular reflection from a random rough magnesium oxide ceramic surface is analyzed by using the geometric optics approximation method. Then, the geometric optics approximation method is employed to develop a theoretical model to predict the observation effect of the grazing-angle scattering phenomenon of the road surface. The rough surface is assumed to consist of small-scale rough surface facets. The road surface mirage is reproduced from a large number of small-scale rough surface facets within the eye's resolution limit at grazing scattering angles, as the average bidirectional reflectance distribution function value at the bright location is about twice that of the surface in front of the mirage. It is suggested that the light-enhancing effect of the rough surface under grazing-angle scattering is not proper to be termed as "off-specular reflection," since it has nothing to do with the "specular" direction with respect to the incident direction.

Products of the SNPP VIIRS SD Screen Transmittance and the SD BRDFs From Both Yaw Maneuver and Regular On-Orbit Data

To ensure data quality, the Earth-observing Visible Infrared Imaging Radiometer Suite (VIIRS) on the Suomi National Polar-orbiting Partnership satellite regularly performs on-orbit radiometric calibration of its 22 spectral bands. The primary radiance source for the calibration of the VIIRS reflective solar bands (RSBs) is a sunlit onboard solar diffuser (SD). During the calibration process, sunlight goes through a perforated plate (the SD screen) and then strikes the SD. The sunlight, scattered off the SD of near-Lambertian property, is used for the calibration. Consequently, the spectral radiance of the scattered sunlight is proportional to the product of the SD screen transmittance and the SD bidirectional reflectance distribution function (BRDF) value at the observation direction. The BRDF value is decomposed to the product of its initial value at launch and a numerical degradation factor that quantifies the decrease from the initial value. The degradation factor is determined by an onboard SD stability monitor (SDSM). During the BRDF degradation factor determination process, the SDSM receives the SD scattered sunlight and the sunlight that goes through another perforated plate at almost the same time. The ratio of the signal strengths from the two observations is used to determine the BRDF degradation factor. Consequently, the RSB radiometric calibration requires the accurate knowledge of the product of the SD screen transmittance and the initial BRDF value as sensed by the RSB and the SDSM detectors. We use both yaw maneuver and a small portion of regular on-orbit data to determine the products.

Suomi NPP VIIRS Solar Diffuser BRDF Degradation Factor at Short-Wave Infrared Band Wavelengths

The Visible Infrared Imaging Radiometer Suite (VIIRS) aboard the Suomi National Polar-orbiting Partnership (SNPP) satellite is an imaging radiometer, collecting data of the Earth's surface in wavelengths ranging from 0.41 to 12.5 μm. To maintain and improve data quality, the VIIRS calibrates its reflective solar bands using a sunlit onboard solar diffuser (SD) panel as the radiance source. Due to exposure to solar radiative energy and high-energy particles and perhaps on-orbit contamination, the surface property of the SD panel changes with time. An onboard SD stability monitor (SDSM) measures the change in the value of the bidirectional reflectance distribution function (BRDF) of the SD at the SDSM SD view direction. The SDSM measurements show that the BRDF value decreases over time and that the degradation is wavelength dependent. The degradation varies monotonically with the wavelength and becomes much smaller at a longer wavelength. However, the SDSM design band wavelengths (412-926 nm) are much shorter than the VIIRS short-wave infrared (SWIR) band wavelengths (1238-2257 nm). Consequently, for simplicity, for SNPP VIIRS, it has been assumed that the degradation is zero at the SWIR band wavelengths. Nevertheless, at the present time, the degradation at the shorter end of the SWIR band wavelengths may not be small enough to be negligible to satisfy the 0.1% (at least) radiometric calibration stability required by the Ocean Color products. We propose empirical models to calculate the BRDF degradation in the SWIR wavelength region.

Modeling the bidirectional reflectance distribution function of seawater with spilt oil

Study on the bidirectional reflectance distribution function (BRDF) of seawater with spilt oil will provide a theoretical basis for detection of oil film on sea surface and oil emulsion in sea water, which will be of great significance for protection of marine environment and marine ecological balance. In this paper a model of BRDF for oil-polluted seawater has been developed by applying Monte Carlo method and Mie scattering theory. The BRDFs of clean seawater, oil-covered seawater, and oil-emulsion seawater are investigated at wavelengths of 532 nm and 355 nm. Simulation results of different film thicknesses and oil emulsion concentrations are presented. Results show that the BRDF is rather sensitive to the degree of pollution in seawater. The presence of oil film or oil emulsion will cause a decrease of the BRDF. At the same angles of observation, the BRDF value of seawater decreases with the increase of oil film thickness and oil emulsion concentration. Oil spill detecting and monitoring can potentially be achieved using BRDF data from optical sensors.

Calibration of remote sensing image using BRDF model

A new bidirectional reflectance distribution function (BRDF) model of earth objects is established for the calibration of remote sensing image by the national metrology equipment. This model colligates the solar radiance, the atmosphere status, the object type, and the space camera parameter, etc. The output data of this model is the enter radiance data for the space camera. The remote sensing image can be appeared more “true” through this calibration. A kind of ground glass for architecture is measured and the correspond remote sensing image is simulated. After calibrated, the chromatism of this image is improved by 2 and the luminance contrast of that is improved by 3. OCIS codes: 120.0120, 280.0280, 290.0290. doi: 10.3788/COL201210.S11201. The aero camera receives different radiance and emit different wavelength light at the same time for the generation of the remote sensing image. Bidirectional reflectance distribution function (BRDF) combine these incident light, reflect light, and scatter light in one variable and it is the best variable to describe the space radiance performance of objects. The complex BRDF model for remote sensing image is based on the BRDF fundament equation, and colligates the solar radiance, the atmosphere status, the object type, and the space camera parameter, etc. In this model, the solar radiance and it’s change through atmosphere are considered in the incident variable of BRDF, and the proximity effect of atmosphere and the parameters of aero camera are considered for the reflect variable of BRDF, for example, the BRDF performance of aerosol [1] . Then the BRDF value of some typical objects are measured and calibrated. The absolute BRDF value are achieved and simulated using the complex BRDF model. Thus the remote sensing image which is calibrated is achieved. The whole procedure is shown in Fig.1. The basement equation of the complex BRDF model is established by the definition of BRDF as shown in Eq.(1) which defined as the ration of the reflect radiance and the incident irradiance on the appearance of the objects [2] . In Eq.(1), �i represents the incident zenith angle, 'i represents the incident azimuth angle, �r represents the incident zenith angle, 'r represents the incident azimuth angle, � the represents wavelength, Lr(�i,'i,�r,'r,�) represents the reflect radiance at specified angles and wavelength, Ei(�i,'i,�) represents the incident irradiance at specified angles and wavelength. Equation (1) is true in the controllable incident solid angle d i, which is shown in Fig.2. Under this condition, Lr(�i,'i,�r,'r,�) can be simplified to Lr(�r,'r,�). fr(�i,'i,�r,'r,�) = dLr(�i,'i,�r,'r,�) dEi(�i,'i,�) = Lr(�r,'r,�) Ei(�i,'i,�) .

Carbon aerogel: a new nonreflective material for the infrared

We present directional hemispherical reflectance (DHR) and bidirectional reflectance distribution function (BRDF) measurements of a carbon aerogel in the 2.5-14.3-microm infrared spectral region. The measured DHR is 1.0-1.2 +/- 0.2% throughout the 2.5-14.3-microm infrared wavelength region. When the incidence angle is increased from 8 degrees to 30 degrees off normal, the DHR increases by only 0.2%; i.e., performance does not significantly degrade as a result of illumination by off-normal infrared radiation. BRDF measurements, obtained at a wavelength of 10.6 microm, indicate that carbon aerogel exhibits Lambertian behavior. The carbon aerogel's BRDF value of 4 x 10(-3) sr(-1) is consistent with its measured DHR values. Gas adsorption and transmission-electron microscopy indicate a structure dominated by particles and pores of <or=10-nm dimension. Scanning-electron microscopy reveals surface roughness on a scale of tens of nanometers. The DHR and BRDF of carbon aerogel compare favorably with those of Martin Black and Rippey, two widely used nonreflective materials.

Optical scattering enhanced by silicon micromachined surfaces

Advanced semiconductor detection devices incorporate surface texturing to reduce the reflection of incident radiation, and thus, enhance optical absorption through scattering. Using micromachining techniques, three different silicon surfaces were fabricated, optically characterized, and analyzed in terms of their ability to scatter incident optical energy. The fabricated surfaces consist of randomly sized and spaced pyramids (RSSPs), deep vertical-wall grooves (DVWGs), and porous silicon (PS). The RSSP textured surfaces consist of randomly-sized pyramids whose square base widths and heights span 0.5–12.0 μm, but otherwise manifest consistent shape and symmetry. The pyramid walls form an angle of 54.74° with respect to the surface of the sample. The DVWG structures consist of interdigitated, 270- μm deep, 25- μm wide, and 1000- μm long grooves separated by 5- μm wide walls. The porous silicon samples consist of surfaces with etched random pores that are 0.2–5- μm deep, 1–5- μm long, and 0.1–5- μm wide. Utilizing laser scatterometry, the bi-directional reflectance distribution function (BRDF) of the silicon textured surfaces was measured at commercially available laser wavelengths of 1.06 and 10.6 μm. A highly-polished, single-crystal silicon wafer was used as a reference surface. The three micromachined surfaces manifested enhanced scattering at 1.06 μm, as demonstrated by a reduced specular peak and increased average BRDF. The RSSP textured surface also demonstrated a small BRDF value at the 10.6- μm illumination laser wavelength.