TERAHERTZ-FREQUENCY SPECTROSCOPY AS A TECHNIQUE FOR THE REMOTE DETECTION OF BIOLOGICAL WARFARE AGENTS
This paper discusses the potential use of terahertzfrequency spectroscopy as a technique for the remote detection of biological warfare agents. Here, design studies are presented for a differential-absorption-radar (DAR) approach that utilizes the spectral signatures of Bacillus (B.) subtillus spores within the terahertz (THz) regime as the detection mechanism. The signature data used in these studies is taken from laboratory measurements performed on uniform thin films of B. subtillus spores and the system performance is assessed for both incoherent and coherent detector modalities. These studies consider DAR remote sensing of biological (bio) clouds at significant ranges (i.e., 1 km) and include the effects of realistic atmospheric conditions. Specifically, THz spectral signatures were used in a highlevel remote-sensor design to estimate the probabilities of detection (Pd) and false-alarm (Pfa) associated with this general technique. The system design studies suggest useful remote-detection performance can be achieved (i.e., Pd > 0.9 & Pfa << 10 for bio-cloud densities < 10 cm) at 1 km ranges if the THz signature information remains predictably stable under varying atmospheric conditions (e.g., changes in humidity, spore activity state, etc). Hence, this paper will also present recent results from scientific studies on bio-molecules that are exploring the underlying mechanisms responsible for the spectral signatures. DAR system performance is also assessed in a more practical bio-warfare military or civilian defense scenario. Here, the Pd and Pfa statistics for the DAR system are mapped onto the time-dependent evolution of an aerosol bio-cloud release to give a real-time indication of the effectiveness of the detection methodology. All together, these results demonstrate that standoff detection of bio-agents is feasible for threat-level concentrations in practical battlefield environments at sufficient ranges to provide for early warning.
Terahertz and millimetre wave technology in port and harbour security
The terahertz region of the electromagnetic spectrum is typically defined in the frequency range 100 GHz to 10 THz, corresponding to a wavelength range of 3 mm to 30 microns. The millimetre wave region lies between 30 GHz and 300 GHz, corresponding to a wavelength range of 10 cm to 1 mm and overlaps a portion of the terahertz region. Following the development of coherent sources and detectors in the early eighties, there has been growing interest in the role of terahertz technology for security and defence. The terahertz region offers a huge expanse of unused bandwidth, which currently presents a significant advantage for both security and defense initiatives. The ability of terahertz radiation to probe intermolecular interactions, large amplitude vibrations and rotational modes, in addition to showing polarization sensitivity makes terahertz radiation a unique and diverse region of the electromagnetic spectrum. The additional ability of both terahertz and millimeter wave radiation to 'see through' common materials, such as thick smoke, fog and dust, which are often considered as opaque in other regions of the electromagnetic spectrum offers further advantages over other optical techniques. Due to the heavy attenuation of terahertz radiation by water vapour, millimeter wave technology is more suited for long range, all-weather imaging systems, whereas terahertz technology has more potential for high resolution short range imaging and spectroscopy. The potential of terahertz and millimetre wave technology and their associated potential for port and harbour security initiatives are discussed.
Germination ecology of Central Asian Stipa spp: differences among species, seed provenances, and the importance of field studies
Stipa-species are wide-spread in Central Asia, but sexual reproduction in the dry steppes is rare. To facilitate conservation and restoration of these important rangelands, we studied germination characteristics of three common Mongolian Stipa-species under field- and lab conditions. Seeds of Stipa krylovii, Stipa gobica and Stipa glareosa were sown at the study site in Southern Mongolia over two consecutive years during which period tests were carried out to ascertain whether competition or herbivory are the main constraints of seedling establishment. In addition, we tested germination and seed viability in the laboratory under two different temperature regimes (20/10°C and 8/4°C), as well as the effect of cold-stratification. The lab experiments also included S. krylovii seeds originating from three climatically different provenances. None of the three Stipa-species seedlings emerged during the first 2 years of the field study. However, after an unusually intense rain event in the third year, 3% of S. krylovii, 0.6% of S. glareosa and 0.1% of S. gobica seeds germinated in the study plots. The factors ‘sowing-year’ and ‘vegetation’ significantly affected seedling emergence, whereas grazing had no effect at all. Under laboratory conditions a high percentage of viable seeds of S. gobica and S. glareosa germinated at both incubation temperatures, and cold-stratification had no effect on germination or viability. Germination of S. krylovii seeds required warmer temperatures and cold-stratification had a positive effect. Such evidence for dormancy was more pronounced in seeds from the moister, northern provenances. Germination of Stipa-species in the field is rare and only possible under exceptionally moist conditions. Conservation should thus concentrate on steppe conservation rather than on restoration. Where artificial reseeding is necessary, differences among species and also among different seed provenances should be taken into account.