Searching for the IRA 'disappeared': Ground-penetrating radar investigation of a churchyard burial site, Northern Ireland

A search for the body of a victim of terrorist abduction and murder was made in a graveyard on the periphery of a major conurbation in Northern Ireland. The area is politically sensitive and the case of high profile. This required non-invasive, completely non-destructive and rapid assessment of the scene. A MALA RAMAC ground-penetrating radar system was used to achieve these objectives. Unprocessed and processed 400MHz data shows the presence of a collapse feature above and around a known 1970s burial with no similar collapse above the suspect location. In the saturated, clay-rich sediments of the site, 200MHz data offered no advantage over 400MHz data. Unprocessed 100MHz data shows a series of multiples in the known burial with no similar features in the suspect location. Processed 100MHz lines defined the shape of the collapse around the known burial to 2m depth, together with the geometry of the platform (1m depth) the gravedigger used in the 1970s to construct the site. In addition, processed 100MHz data showed both the dielectric contrast in and internal reflection geometry of the soil imported above the known grave. Thus the sequence, geometry, difference in infill and infill direction of the grave was reconstructed 30 years after burial. The suspect site showed no evidence of shallow or deep inhumation. Subsequently, the missing person������¢���¯���¿���½���¯���¿���½s body was found some distance from this site, vindicating the results and interpretation from ground-penetrating radar. The acquisition, processing, collapse feature and sequence stratigraphic interpretation of the known burial and empty (suspect) burial site may be useful proxies for other, similar investigations. GPR was used to evaluate this site within 3 hours of the survey commencing, using unprocessed data. An additional day of processing established that the suspect body did not reside here, which was counter to police and community intelligence.

Charge-state distribution and Doppler effect in an expanding photoionized plasma.

The charge state distributions of Fe, Na, and F are determined in a photoionized laboratory plasma using high resolution x-ray spectroscopy. Independent measurements of the density and radiation flux indicate unprecedented values for the ionization parameter ���¾=20 25 erg cm s-1 under near steady-state conditions. Line opacities are well fitted by a curve-of-growth analysis which includes the effects of velocity gradients in a one-dimensional expanding plasma. First comparisons of the measured charge state distributions with x-ray photoionization models show reasonable agreement.

Doppler cooling of gallium atoms: 1. Fine structure effects and transient coherences

A realistic model of the dipole radiation forces in transverse Doppler cooling (with a s+-s- laser configuration) of an atomic beam of group 13 elements is studied within the quantum-kinetic equation framework. The full energy level sub-structure for such an atom with I = 0 (such as 66Ga) is analysed. Two cooling strategies are investigated; the first involving the 2P3/2 ? 2D5/2 transition and the second a dual laser cooling experiment involving transitions 2P1/2 and 2P3/2 ? 2S1/2. The latter scheme creates a velocity-independent dark-state resonance that inhibits a steady-state dipole cooling force. However, time-dependent calculations show that transient cooling forces are present that could be exploited for laser cooling purposes in pulsed laser fields.

Stokes imaging, Doppler mapping and Roche tomography of the AM Herculis system V834 Cen

We report on new simultaneous phase-resolved spectroscopic and polarimetric observations of the polar (AM Herculis star) V834 Cen during a high state of accretion. Strong emission lines and high levels of variable circular and linear polarization are observed over the orbital period. The polarization data are modelled using the Stokes imaging technique of Potter et al. The spectroscopic emission lines are investigated using the Doppler tomography technique of Marsh and Horne and the Roche tomography technique of Dhillon and Watson. Up to now, all three techniques have been used separately to investigate the geometry and accretion dynamics in cataclysmic variables. For the first time, we apply all three techniques to simultaneous data for a single system. This allows us to compare and test each of the techniques against each other and hence to derive a better understanding of the geometry, dynamics and system parameters of V834 Cen.

Under-water scene investigation using ground penetrating radar (GPR) in the search for a sunken jet ski, Northern Ireland

A search for a submerged jet ski and the lost limb of its driver involved in a collision with a speedboat was made in a shallow lake in Northern Ireland. The location of both was crucial to establishing events at the time of the accident. Local intelligence suggested both objects were likely to be partially-buried by lacustrine silt. To avoid sediment churning, this required non-invasive, completely non-destructive assessment and mapping of the scene. A MALA RAMAC ground-penetrating radar system (GPR) mounted on floats for surveying from walkways and jetties or placed in a small rubber dinghy for offshore profiling was used. A grid was established and each line surveyed with 100, 200 and 400MHz antennae. In waters over 6m deep GPR data showed the form of the lake floor but excessive ringing occurred in the data. In waters less than 6m deep ringing diminished on both 100 and 200MHz data, the latter displaying the best trade-off between depth penetration and horizontal object resolution. 400MHz data failed to be of use in waters over 2m deep and at these depths showed only limited improvement of image quality compared to 200MHz data. Surface objects such as a wooden walkway caused interference on 200 and 400MHz data when antennae were oriented both normal and parallel to survey direction; this may be a function of the low attenuation of radar waves in freshwater, allowing excellent lateral and vertical radar wave penetration. On 200MHz data the damaged jet-ski was clearly imaged in a location that contradicted the speedboat driver's account of the accident.

EFFECT OF SURFACE RESISTOR LOADING ON HIGH-IMPEDANCE SURFACE RADAR ABSORBER RETURN LOSS AND BANDWIDTH

A simple method for the selection of the appropriate choice of surface-mounted loading resistor required for a thin radar absorber based on a high-impedance surface (HIS) principle is demonstrated. The absorber consists of a HIS, (artificial magnetic ground plane), thickness 0.03 lambda(0) surface-loaded resistive-elements interconnecting a textured surface of square patches. The properties of absorber are characterized under normal incident using a parallel plate waveguide measurement technique over the operating frequency range of 2.6-3.95 GHz. We show that for this arrangement return loss and bandwidth are insensitive to +/- 2% tolerance variations in surface resistor values about the value predicted using the method elaborated in this letter, and that better than -28 dB at 3.125 GHz reflection loss can be obtained with an effective working bandwidth of up to 11% at -10 dB reflection loss. (C) 2009 Wiley Periodicals, Inc. Microwave Opt Technol Lett 51: 1733-1775, 2009; Published online in Wiley Interscience (www.interscience.wiley.com). DOI 10.1002/mop.24454