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 Frequency Sensing and Imaging: A Time of Reckoning Future Applications?
In recent years, the field of terahertz (THz) science and technology has entered a completely new phase of unprecedented expansion that is generating ever growing levels of broad-based international attention. In particular,there have been important advances in state-of-the-art THz technology and very enthusiastic growth in research activities associated with related scientific and industrial applications. One can legitimately argue that the potential payoffs of THz sensing and imaging (THz S&I) to application areas such as defense, security, biology and medicine are the major drivers of this new phenomenon. However, there remain major science and technology "gaps" in the THz regime that must be reconciled before many of the perceived payoffs ever become realizable. Therefore, it is natural to ask the question "Is now the time for THz?" or rather, are these recent events just a repeat of previous cycles in THz overenthusiasm that have been witnessed during the last century? The main goal of this paper is to consider some of the most promising THz S&I applications within the specific context of their particular science and technology challenges in an attempt to credibly judge (or speculate on) their future potential.
The Tsetse Problem on the Eastern Cattle Route in the Gold Coast
1. Primary fly-belts round Makongo consisted of three different vegetational communities: a Cynometra-Vitex association along the main length of the Makongo river, on a clay soil; a Ficus congensis association along the river close to the town, on a sandy soil; and Isoberlinia doka woodland on moist sandy soil north-west and south of Makongo. 2. Secondary fly-belts of less dense vegetation occur in the orchard bush savannah round Makongo, and these are not colonised until the commencement of the rainy season. 3. Glossina tachinoides and G. palpalis both occurred in the riverside communities, and G. palpalis alone in the Isoberlinia woodland. 4. Along the river G. palpalis outnumbered G. tachinoides by 3:1 in the dry season. At the commencement of the rains G. tachinoides increased more quickly than G. palpalis , bringing their numbers very nearly equal, but at the end of the rains there was a decrease in G. tachinoides which restored the original proportion. 5. G. morsitans had been found at Makongo formerly but was not met with at the time of this investigation, its absence being due to the disappearance of the larger antelope from the neighbourhood. 6. Smaller game animals, small mammals and reptiles afforded an adequate food supply for tsetse in the fly-belts, and also passing herds of cattle, as well as natives from the village and travellers. 7. The distribution of G. palpalis within the fly-belts was markedly influenced by the proximity of a cattle road along which herds of cattle passed almost daily, and by village water-holes. 8. During the dry season the primary foci were always found to be the places of greatest relative humidity, and the fly does not tend to move out of these until the general atmospheric humidity has reached a certain fairly high degree. 9. In clearing the fly-belts the removal of all primary foci within a quarter of a mile of the town and of thick bush within 100 yards of water-holes was undertaken. The work lasted from the beginning of February to the end of March 1931. 10. The effect of clearing the Isoberlinia doka woodland was to banish G. palpalis completely, and it never returned to these clearings. 11. On clearing the riverside Ficus congensis fly-belt, G. tachinoides was practically eliminated for the first three months, but reappeared in the clearings in June when there was a general increase and up-stream migration of this fly. G. palpalis remained in this clearing in fluctuating numbers up to June, when observations were suspended. 12. 565 marked tsetse were liberated in the fly-belts immediately previous to clearing. Of G. palpalis 12·7% were recaptured in the clearings and 11% outside the clearings. Of G. tachinoides 5·5% were recaptured in the clearings and 6·8% outside.