The Image Space Reconstruction Algorithm (ISRA) has been used in hyperspectral imaging applications to
monitor changes in the environment and specifically, changes in coral reef, mangrove, and sand in coastal areas.
This algorithm is one of a set of iterative methods used in the hyperspectral imaging area to estimate abundance.
However, ISRA is highly computational, making it difficult to obtain results in a timely manner. We present the
use of specialized hardware in the implementation of this algorithm, specifically the use of VHDL and FPGAs
in order to reduce the execution time. The implementation of ISRA algorithm has been divided into hardware
and software units. The hardware units were implemented on a Xilinx Virtex II Pro XC2VP30 FPGA and the
software was implemented on the Xilinx Microblaze soft processor. This case study illustrates the feasibility
of this alternative design for iterative hyperspectral imaging algorithms. The main bottleneck found in this
implementations was data transfer. In order to reduce or eliminate this bottleneck we introduced the use of
block-rams (BRAMS) to buffer data and have data readily available to the ISRA algorithm. The memory
combination of DDR and BRAMS improved the speed of the implementation.
Results demonstrate that the C language implementation is better than both FPGA's implementations.
Nevertheless, taking a detailed look at the improvements in the results, FPGA results are similar to results
obtained in the C language implementation and could further be improved by adding memory capabilities to the
FPGA board. Results obtained with these two implementations do not have significant differences in terms of
execution time.
A fundamental challenge to Remote Sensing is mapping the ocean floor in coastal shallow waters where variability, due to the interaction between the coast and the sea, can bring significant disparity in the
optical properties of the water column. The objects to be detected, coral reefs, sands and submerged aquatic vegetation, have weak signals, with temporal and spatial variation. In real scenarios the absorption and backscattering coefficients have spatial variation due to different sources of variability (river discharge, different depths of shallow waters, water currents) and temporal fluctuations. This paper presents the development of algorithms for retrieving information and its application to the recognition, classification
and mapping of objects under coastal shallow waters. A mathematical model that simplifies the radiative transfer equation was used to quantify the interaction between the object of interest, the medium and the sensor. The retrieval of information requires the development of mathematical models and processing tools in the area of inversion, image reconstruction and detection. The algorithms developed were applied to one set of remotely sensed data: a high resolution HYPERION hyperspectral imagery. An inverse problem arises as this spectral data is used for mapping the ocean shallow waters floor. Tikhonov method of regularization was used in the inversion process to estimate the bottom albedo of the ocean floor using a priori information in the form of stored spectral signatures, previously measured, of objects of interest, such as sand, corals, and sea grass.
KEYWORDS: Waveguides, Finite element methods, Refractive index, Near field, Single mode fibers, Near field optics, Chemical elements, Interfaces, Cladding, Reconstruction algorithms
We show that the refractive-index profile (RIP) of optical waveguides can be determined by analyzing the transmitted near-field pattern with the finite element method. The first step consists in determine the initial guess for the RIP. Then, the selected guess is improved applying a reconstruction procedure with the finite element method. The procedure has been evaluated by comparing the obtained results with experimental measurements obtained by the RNF and m-lines techniques on a pure-silica single-mode fiber and slab waveguide, respectively.
A novel and efficient method for Bessel beams generation is proposed. It relies on using a toroidal zone plate as an element forming the ring focus and subsequent Fourier transforming of the ring focus into the Bessel beam. The proposed solution, thanks to focusing of all illuminating wave into the ring focus allows to achieve greater efficiency than earlier solutions. Moreover it enables to generate higher order Bessel beams by adding a linear angular phase term to the transmittance of the zone plate. The proposed method is confirmed by numerical simulations.
Axicons designed as a tandem of one diverging lens and one converging lens burdened with spherical aberration are analyzed in this report. The principal features of the axicon's focal segment, such as the axial intensity distribution and the central core width, are determined with the help of the nonuniform stationary phase method and compared with the numerical evaluation of the corresponding diffraction integral.
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