Exploration of a Polarized Surface Bidirectional Reflectance Model Using the Ground-Based Multiangle SpectroPolarimetric Imager

Abstract

Accurate characterization of surface reflection is essential for retrieval of aerosols using downward-looking remote sensors. In this paper, observations from the Ground-based Multiangle SpectroPolarimetric Imager (GroundMSPI) are used to evaluate a surface polarized bidirectional reflectance distribution function (PBRDF) model. GroundMSPI is an eight-band spectropolarimetric camera mounted on a rotating gimbal to acquire pushbroom imagery of outdoor landscapes. The camera uses a very accurate photoelastic-modulator-based polarimetric imaging technique to acquire Stokes vector measurements in three of the instrument's bands (470, 660, and 865 nm). A description of the instrument is presented, and observations of selected targets within a scene acquired on 6 January 2010 are analyzed. Data collected during the course of the day as the Sun moved across the sky provided a range of illumination geometries that facilitated evaluation of the OPEN ACCESSAtmosphere 2012, 3 592 surface model, which is comprised of a volumetric reflection term represented by the modified Rahman-Pinty-Verstraete function plus a specular reflection term generated by a randomly oriented array of Fresnel-reflecting microfacets. While the model is fairly successful in predicting the polarized reflection from two grass targets in the scene, it does a poorer job for two manmade targets (a parking lot and a truck roof), possibly due to their greater degree of geometric organization. Several empirical adjustments to the model are explored and lead to improved fits to the data. For all targets, the data support the notion of spectral invariance in the angular shape of the unpolarized and polarized surface reflection. As noted by others, this behavior provides valuable constraints on the aerosol retrieval problem, and highlights the importance of multiangle observations.

IPRT polarized radiative transfer model intercomparison project – Phase A

“…SHDOM has special purpose subroutines for the unpolarized case (N stokes ¼ 1) so the polarized code serves efficiently for scalar calculations. There are two polarized surface reflection models: Fresnel surface with waves [57] used for ocean, and depolarizing modified-RPV (including the hotspot) with polarizing Fresnel reflection from randomly oriented microfacets [8] used for land. When enough memory is available, the surface BRDF is precomputed for all incoming and outgoing discrete ordinates, greatly speeding up computation for uniform nonLambertian surfaces.…”

“…The Research Scanning Polarimeter (RSP) [6,7] has been used for ground-based as well as airborne aerosol measurements. Other multi-channel polarimetric instruments are the Airborne Multiangle SpectroPolarimetric Imager (AirMSPI) [8] and the Observing System Including PolaRisation in the Solar Infrared Spectrum (OSIRIS) [9]. The commercially available ground-based polarimeter, CE318-DP, developed by CIMEL Electronic (Paris, France) is now available at several AERONET stations [10].…”

Using remote sensing to detect the polarized sunglint reflected from oil slicks beyond the critical angle

“…The Stokes parameters of the sunglint reflected from the calm surface of an oil slick or seawater can be expressed as [ I o , Q o , U o , V o ] T . The Mueller matrix, which is a polarized state transformation matrix [ Priest and Meier , ; Diner et al ., ], connects the Stokes vectors for the directly incident and reflected sunlight. At the interface between two different isotropic, homogeneous media, the Mueller matrix ( M ) can be expressed as where Δ is the phase difference between the sunglint s and p‐polarization parameters.…”

Improving Remote Sensing of Aerosol Optical Depth over Land by Polarimetric Measurements at 1640 nm: Airborne Test in North China

“…Laboratory and airborne measurements indicate that the polarized reflectance from several kinds of surfaces, such as forest, vegetation and bare soils, are spectrally neutral from the visible to SWIR bands [13][14][15][32][33][34], which is consistent with the hypothesis that the surface reflected polarization is generated mainly by the specular reflection at the surface interface, and it can be approximately modelled based on the Fresnel reflection [30]. Consequently, the polarization measurements at near-infrared or SWIR bands (i.e., 1640 nm) corrected for atmospheric effect can derive the polarized surface reflectance at shorter bands.…”