Gareth Dafydd Lewis

Royal Military Academy · Department of Communication, Information, Systems and Sensors (CISS)

Aviation is exceptionally vulnerable to man-portable missile attacks (MANPADS), particularly during the critical stages of flight, e.g., take-off and landing. Consequently, aircraft require a further means of self-protection in addition to pyrotechnic flares. Laser Directed Infrared Countermeasures (DIRCM) target the infrared guidance system presen...

Thermal infrared imaging systems are increasingly vulnerable to the threat of disruption or damage from laser weapons. For laser weapons operating within the waveband of the imager, in-band, the effect is primarily dazzling of the focal plane array. In contrast, for those not in the same waveband, out-of-band, the critical interaction is thermal he...

In this paper, we demonstrate an improvement in the accuracy of a low-cost smart temperature sensor, by measurement of the nonlinear curvature correction at multiple temperature references. The sensors were positioned inside a climate chamber and connected outside to a micro-controller via a network cable. The chamber temperature was increased syst...

In this paper, we describe the temperature and thermal variations from a painted geometrical target (CUBI) fitted with a network of internally mounted 1-wire temperature sensors. The sensors, which were calibrated in a temperature-controlled oven, were recorded every 20 seconds over a period from May to December 2015. This amounts to an archive of...

The continued interest in bistatic polarimetric radar, particularly for SAR applications, has resulted in the requirement for additional simple, well characterized targets for external calibration. These targets must enable both bistatic and polarimetric radar modes to be calibrated, often to a precision of less than 1 dB. Previous research has sho...

The polarimetric probability distribution functions (PDFs) of laser speckle for incident linear and circular polarization states have been determined from the measured Stokes parameters for a limited range of targets that may be encountered in remote sensing applications: two rough surface samples, and two samples which exhibit both surface and vol...

A performance evaluation of several existing polarimetric calibration techniques for bistatic radar cross section (RCS) measurements is in progress. Several calibration test objects, including: cylinders, a dihedral, a trihedral, a sphere, and other noncanonical objects were measured at the European Microwave Signature Laboratory (EMSL), Joint Rese...

Several popular bistatic calibration techniques are evaluated, and comparisons are made between the relative merits of various calibration objects. This analysis considers the following: sensitivity to object alignment error, sensitivity to polarization impurity, and ease of implementation. Both theoretical concepts and practical considerations are...

A performance evaluation of several existing polarimetric calibration techniques for bistatic radar cross section (RCS) measurements was performed. Several calibration test objects, including cylinders, a dihedral, a trihedral, a sphere, and other non-canonical objects were measured at the European Microwave Signature Laboratory (EMSL), Joint Resea...

This paper deals with the depolarization properties of rough surface back-scattering at visible and infra-red wavelengths. It is well known that rough surfaces depolarize incident light. In this paper we analyze the structure of surface depolarization using a coherency matrix approach and show that quantitative estimates of roughness may be obtaine...

This paper presents the results of a calculation of the low-order statistical properties of radiation which has been scattered by small spheroidal particles distributed at different heights above a surface. The results are in the form of analytical formulae for the average scattered intensity and for the normalized second moment of the intensity fl...

A comparison is made between the backscattering Mueller matrices of two bead-blasted aluminium samples at both 632.8nm HeNe and 10.6micrometers CO2 lasers wavelengths. The samples are bead-blasted at two blasting pressures to vary the rms surface roughness and slope. These surfaces are characterized using a mechanical profilometer. Mueller matrices...

We describe a method for increasing target contrast within a turbid medium by means of the polarization state of the scattered light. The backscattered Mueller matrices for various concentrations of 0.1-µm spherical scatterers were measured with and without a painted metal target. Simple discrimination based on detecting cross-polarized intensities...

A study of cross-polarized and copolarized intensities backscattered from roughened aluminum surfaces is presented for both linear and circular incident polarization states. The angular variation of measured Mueller matrices is shown to contain only diagonal elements, as predicted by the reciprocity theorem. The ratio of cross-depolarized to copola...

The backscattering Mueller matrices for a range of bead- blasted aluminium samples having a range of surface roughness and slopes are investigated using a 632.8nm linearly polarized HeNe laser. The analyzing polarizing optics and detector are fixed in the backscattering direction and the angle of incidence varied from 0 degrees to 90 degrees. A com...

Ellipsometer measurements of the effective complex refractive index at a wavelength of 10.6 μm are made on a series of glass and aluminum surfaces of increasing surface roughness. The measured values are then used to calculate the degree of emission polarization and are shown to be in agreement with the experimentally determined values when depolar...

The 8 - 12 micrometer polarization signatures of diffuse and specular aluminum geometrical darts were analyzed outdoors using a polarization sensitive thermal imager. Results of the degree and plane of polarization are presented for different thermal imager gain bands and weather conditions during a two week period. The 0 degree, 45 degree, 90 degr...

Plastic mines are cheap, small, and difficult to detect using current methods. IR polarization discrimination where the mines present themselves as a flashing signal may be of potential benefit in finding surface laid or scattered types in a cluttered background. Results from a laboratory study show that plastic has significant 8-14 micrometers IR...

Infrared measurements are presented of the degree of linear polarization of thermally emitted radiation from metallic and glass surfaces. Both types of surface show a rapid increase with target angle of the degree of linear polarization and a rapid fall with increasing surface roughness.

Target detection using passive electro-optic devices operating in the 8 to 14 micron band is often limited by background clutter. A possible method of overcoming this limitation may be to use the polarization content of the image to discriminate between man-made targets and natural background. Laboratory measurements are presented of the polarizati...