22,611 research outputs found
A Novel Stealthy Target Detection Based on Stratospheric Balloon-borne Positional Instability due to Random Wind
A novel detection for stealthy target model F-117A with a higher aspect vision is introduced by using Stratospheric Balloon-borne Bistatic system. The potential problem of proposed scheme is platform instability impacted on the balloon by external wind force. The flight control system is studied in detail under typical random process, which is defined by Dryden turbulence spectrum. To accurately detect the stealthy target model, a real Radar Cross Section (RCS) based on physical optics (PO) formulation is applied. The sensitivity of the proposed scheme has been improved due to increasing PO – scattering field of stealthy model with higher aspect angle comparing to the conventional ground -based system. Simulations demonstrate that the proposed scheme gives much higher location accuracy and reduces location errors
Dynamic Response of a fast near infra-red Mueller matrix ellipsometer
The dynamic response of a near infrared Ferroelectric Liquid Crystal based
Mueller matrix ellipsometer (NIR FLC-MME) is presented. A time dependent
simulation model, using the measured time response of the individual FLCs, is
used to describe the measured temporal response. Furthermore, the impulse
response of the detector and the pre-amplifier is characterized and included in
the simulation model. The measured time-dependent intensity response of the MME
is reproduced in simulations, and it is concluded that the switching time of
the FLCs is the limiting factor for the Mueller matrix measurement time of the
FLC-based MME. Based on measurements and simulations our FLC based NIR-MME
system is estimated to operate at the maximum speed of approximately 16 ms per
Mueller matrix measurement. The FLC-MME may be operated several times faster,
since the switching time of the crystals depends on the individual crystal
being switched, and to what state it is switched. As a demonstration, the
measured temporal response of the Mueller matrix and the retardance of a thick
liquid crystal variable retarder upon changing state is demonstrated.Comment: to be published in Journal of Modern Optics 20 pages, 6 figure
Three-dimensional scanning of specular and diffuse metallic surfaces using an infrared technique
For the past two decades, the need for three-dimensional (3-D) scanning of industrial objects has increased significantly and many experimental techniques and commercial solutions have been proposed. However, difficulties remain for the acquisition of optically non-cooperative surfaces, such as transparent or specular surfaces. To address highly reflective metallic surfaces, we propose the extension of a technique that was originally dedicated to glass objects. In contrast to conventional active triangulation techniques that measure the reflection of visible radiation, we measure the thermal emission of a surface, which is locally heated by a laser source. Considering the thermophysical properties of metals, we present a simulation model of heat exchanges that are induced by the process, helping to demonstrate its feasibility on specular metallic surfaces and predicting the settings of the system. With our experimental device, we have validated the theoretical modeling and computed some 3-D point clouds from specular surfaces of various geometries. Furthermore, a comparison of our results with those of a conventional system on specular and diffuse parts will highlight that the accuracy of the measurement no longer depends on the roughness of the surface
Achromatizing a liquid-crystal spectropolarimeter: Retardance vs Stokes-based calibration of HiVIS
Astronomical spectropolarimeters can be subject to many sources of systematic
error which limit the precision and accuracy of the instrument. We present a
calibration method for observing high-resolution polarized spectra using
chromatic liquid-crystal variable retarders (LCVRs). These LCVRs allow for
polarimetric modulation of the incident light without any moving optics at
frequencies >10Hz. We demonstrate a calibration method using pure Stokes input
states that enables an achromatization of the system. This Stokes-based
deprojection method reproduces input polarization even though highly chromatic
instrument effects exist. This process is first demonstrated in a laboratory
spectropolarimeter where we characterize the LCVRs and show example
deprojections. The process is then implemented the a newly upgraded HiVIS
spectropolarimeter on the 3.67m AEOS telescope. The HiVIS spectropolarimeter
has also been expanded to include broad-band full-Stokes spectropolarimetry
using achromatic wave-plates in addition to the tunable full-Stokes
polarimetric mode using LCVRs. These two new polarimetric modes in combination
with a new polarimetric calibration unit provide a much more sensitive
polarimetric package with greatly reduced systematic error.Comment: Accepted in PAS
Recommended from our members
Astigmatism and Pseudoaccommodation in Pseudophakic Eyes
noAdvanced IOLs with circumferential zones of different power provide pseudoaccommodation. We investigated the potential for power variation with meridian, namely astigmatism, to provide pseudo-accommodation. With appropriate power and axis orientations, acceptable pseudo-accommodation can be achieved
A 3D scanner for transparent glass
Many practical tasks in industry, such as automatic inspection or robot vision, often require the scanning of three-dimensional shapes by use of non-contact techniques. However, few methods have been proposed to measure three-dimensional shapes of transparent objects because of the difficulty of dealing with transparency and specularity of the surface. This paper presents a 3D scanner for transparent glass objects based on Scanning From Heating (SFH), a new method that makes use of local surface heating and thermal imaging
- …