Jon Kåre Lotsberg

Monte Carlo and discrete-ordinate simulations of irradiances in the coupled atmosphere-ocean system

We compare Monte Carlo (MC) and discrete-ordinate radiative-transfer (DISORT) simulations of irradiances in a one-dimensional coupled atmosphere-ocean (CAO) system consisting of horizontal plane-parallel layers. The two models have precisely the same physical basis, including coupling between the atmosphere and the ocean, and we use precisely the same atmospheric and oceanic input parameters for both codes. For a plane atmosphere-ocean interface we find agreement between irradiances obtained with the two codes to within 1%, both in the atmosphere and the ocean. Our tests cover case 1 water, scattering by density fluctuations both in the atmosphere and in the ocean, and scattering by particulate matter represented by a one-parameter Henyey-Greenstein (HG) scattering phase function. The CAO-MC code has an advantage over the CAO-DISORT code in that it can handle surface waves on the atmosphere-ocean interface, but the CAO-DISORT code is computationally much faster. Therefore we use CAO-MC simulations to study the influence of ocean surface waves and propose a way to correct the results of the CAO-DISORT code so as to obtain fast and accurate underwater irradiances in the presence of surface waves.

Focusing of electromagnetic waves into a uniaxial crystal

We derive integral representations suitable for studying the focusing of electromagnetic waves through a plane interface into a uniaxial crystal. To that end we start from existing exact solutions for the transmitted fields due to an arbitrary three-dimensional (3D) wave that is incident upon a plane interface separating two uniaxial crystals with arbitrary orientation of the optical axis in each medium. Then we specialize to the case in which the medium of the incident wave is isotropic and derive explicit expressions for the dyadic Greens functions associated with the transmitted fields as well as integral representations suitable for asymptotic analysis and efficient numerical evaluation. Relevant integral representations for focused 3D electromagnetic waves are also given. Next we consider the special case in which (i) the incident field is a two-dimensional (2D) TM wave and (ii) the optical axis in the crystal lies in the plane of incidence, implying that we have a 2D vectorial problem, and derive dyadic Greens functions, integral representations suitable for asymptotic and numerical treatment, and integral representations for focused TM fields. Numerical results for focused 2D TM fields based on these integral representations as well as corresponding experimental results will be presented in forthcoming papers.

Impact of particulate oceanic composition on the radiance and polarization of underwater and backscattered light

We use a Monte Carlo model to investigate how the particulate oceanic composition affects the radiance, the linear polarization, and the circular polarization of underwater and backscattered light. The Mueller matrices used in our simulations were computed using the T-matrix method. They are significantly different for organic and inorganic particles. Our Monte Carlo simulations show that these differences have a significant impact on the underwater and backscattered light, and that it may be possible to determine the ratio between the amounts of organic and inorganic particles from measurements of the full Stokes vector.

Numerical and experimental results for focusing of three-dimensional electromagnetic waves into uniaxial crystals

We present experimental results for focusing of a three-dimensional electromagnetic wave through a plane interface into two different uniaxial crystals, a positive MgF2 crystal and a negative LiNbO3 crystal. These results are compared with numerical results and good agreement is found, both for intensity distributions in various receiving planes and for the locations of the sagittal and tangential focal planes. The theory is briefly outlined both for the exact solution, which includes extraparaxial geometries and double refraction, and for the paraxial solution, in which double refraction is ignored.

Comparisons of exact and paraxial intensities of electromagnetic waves focused into uniaxial crystals

Existing exact and paraxial integral representations for a focused field inside a biaxial crystal are specialized to cases in which we let two of the refractive indices become equal to obtain uniaxially anisotropic media. Focused intensities obtained from the two integral representations are compared and found to be in excellent agreement for paraxial geometries. Paraxial focused fields inside a negative LiNbO3 crystal and a positive MgF2 crystal are studied in some detail.

New versatile setup for goniometric measurements of spectral radiance

We discuss a new versatile setup for goniometric measure- ments of spectral radiances with two modes of operation: 1 it can op- erate as a 2-D goniometer for measurements in a horizontal plane of the singly scattered radiance from particles in suspension and 2 it can be used as a 3-D goniometer for measuring spectral radiances over an entire hemisphere. In our setup, various kinds of light sources and de- tectors can easily be inserted. Among the detectors, a spectral imager is designed and used. Proper hardware and software is chosen so as to make our setup fully automated and easy to operate. We present results from two different investigations to demonstrate the utilization of our setup. The first investigation is concerned with measurements of the volume scattering function VSF over a large forward and backward angular range. Our experimental results for the VSF show good agree- ment with theoretical simulations. We also use our setup to obtain a series of 1-D angular spectral images of the skin on the dorsal side of a human hand in vivo by employing various illumination angles. Our setup provides a robust, highly automated, and flexible framework for carrying out goniometric measurements in a variety of applications.

Discrete ordinate and Monte Carlo simulations of radiative transfer in coupled atmosphere-ocean systems

We present comparisons between deterministic solutions of the vector radiative transfer (RT) equation based on the discrete ordinate (DISORT) method and probabilistic simulations based on the Monte Carlo (MC) method for an atmosphere comprised of either a size distribution of spherical aerosol particles with an average size of 0.3 μm or a size distribution of spherical cloud particles with an average size of 5 μm. Also, we discuss preliminary deterministic results for a coupled atmosphere-ocean system consisting of two turbid media separated by a plane interface across which the refractive index changes abruptly.

Vector Discrete‐Ordinate Radiative Transfer in the Coupled Atmosphere‐Ocean system: CAO‐VDISORT

A computer program has been developed to compute the polarized radiation field in a plane‐parallel medium consisting of two adjacent slabs with different indices of refraction, like the coupled atmosphere‐ocean system. The vertical inhomogeneity of each of the two slabs is accounted for by dividing it into several horizontally homogeneous layers with different scattering and absorption properties. The program, based on vector radiative transfer theory and the discrete‐ordinate method, includes thermal emission, scattering, and absorption in the medium as well as bidirectional reflection and emission at the lower boundary. Possible radiation sources include polarized or unpolarized collimated incident radiation or isotropic illumination at the upper boundary, as well as internal thermal sources. Comparisons with results from Monte Carlo simulations show that this CAO‐VDISORT code provides accurate results for all four elements of the Stokes vector (I, Q, U, and V), and that it is orders of magnitude faster...