KEYWORDS: Imaging systems, Cameras, Data acquisition, Multispectral imaging, Unmanned aerial vehicles, Tunable filters, Data transmission, Image classification, Data processing, Global system for mobile communications
Technological advances in digital imaging and liquid crystal tunable filters allow for a design of a both compact and cost effective multispectral camera system. Thus an image acquisition system for the visible and near infrared wavelength range can be realised consisting of conventional CCD cameras and tunable filters whose spectral transmittace is controlled electronically. Due to their limited internal payload the use of a lightweight, compact camera system is of particular importance for applications involving mini-unmanned-aerial-vehicles (mini-UAVs). Within the scope of this paper a both compact and economical data acquisition system for multispecral images is described. Despite of their limited functionality (e.g.regarding calibration) in comparison with commercial systems such as AVIRIS the use of these upcoming compact multispectral camera
systems can be advantageous in many applications. In order to maintain the systems low weight and price this work proposes to separate data acquisition and processing modules, and transmit pre-processed camera data online to a stationary high performance computer for further processing. Special focus is laid upon transmission paths with limited bandwidth.
Within the scope of this paper a both compact and economical data acquisition system for multispecral images is described. It consists of a CCD camera, a liquid crystal tunable filter in combination with an associated concept for data processing. Despite of their limited functionality (e.g.regarding calibration) in comparison with commercial systems such as AVIRIS the use of these upcoming compact multispectral camera systems can be advantageous in many applications. Additional benefit can be derived adding online data processing. In order to maintain the systems low weight and price this work proposes to separate data acquisition and processing modules, and transmit pre-processed camera data online to a stationary high performance computer for further processing. The inevitable data transmission has to be optimised because of bandwidth limitations. All mentioned considerations hold especially for applications involving mini-unmanned-aerial-vehicles (mini-UAVs). Due to their limited internal payload the use of a lightweight, compact camera system is of particular importance. This work emphasises on the optimal software interface in between pre-processed data (from the camera system), transmitted data (regarding small bandwidth) and post-processed data (based on high performance computer). Discussed parameters are pre-processing algorithms, channel bandwidth, and resulting accuracy in the classification of multispectral image data. The benchmarked pre-processing algorithms include diagnostic statistics, test of internal determination coefficients as well as loss-free and lossy data compression methods. The resulting classification precision is computed in comparison to a classification performed with the original image dataset.
For the numerical prediction of the scattering behavior of arbitrary surfaces the use of a multi pole mthod is a potentially successful way. One reason is its direct addressing of the free space problem, which is primarily not possible with methods such as FEM. For purposes of verification with a reduced set of degrees of freedom the multi pole method is applied on gold plated blazed optical gratings, which are described as surfaces with one-dimensional height function and ideally conductive boundary, leading to a 2D-problem with a simplified matching of the boundary conditions. The geometry is deduced from AFM measurements, numerical results are compared with measurements. An outlook is given on further extensions of the multipole method to 3D-problems with arbitrary boundary conditions such as dielectric layers with losses.
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