Foster S.,Defence Science and Technology Group
Optics InfoBase Conference Papers | Year: 2016
We describe a class of single mode Bragg grating fiber lasers intermediate between DFB and DBR cavities. They possess a number of interesting properties that could be ex-ploited to optimise linewidth, stability and thermo-mechanical coupling in sensor applications. © OSA 2016.
Koks D.,Defence Science and Technology Group
Foundations of Physics | Year: 2017
The disk that rotates in an inertial frame in special relativity has long been analysed by assuming a Lorentz contraction of its peripheral elements in that frame, which has produced widely varying views in the literature. We show that this assumption is unnecessary for a disk that corresponds to the simplest form of rotation in special relativity. After constructing such a disk and showing that observers at rest on it do not constitute a true rotating frame, we choose a “master” observer and calculate a set of disk coordinates and spacetime metric pertinent to that observer. We use this formalism to resolve the “circular twin paradox”, then calculate the speed of light sent around the periphery as measured by the master observer, to show that this speed is a function of sent-direction and disk angle traversed. This result is consistent with the Sagnac Effect, but constitutes a finer analysis of that effect, which is normally expressed using an average speed for a full trip of the periphery. We also use the formalism to give a resolution of “Selleri’s paradox”. © 2017, Her Majesty the Queen in Right of Australia.
Lo K.W.,Defence Science and Technology Group
Journal of the Acoustical Society of America | Year: 2017
When an airborne sound source travels past a stationary ground-based acoustic sensor node in a straight line at constant altitude and constant speed that is not much less than the speed of sound in air, the movement of the source during the propagation of the signal from the source to the sensor node (commonly referred to as the “retardation effect”) enables the full set of flight parameters of the source to be estimated by measuring the direction of arrival (DOA) of the signal at the sensor node over a sufficiently long period of time. This paper studies the possibility of using instantaneous frequency (IF) measurements from the sensor node to improve the precision of the flight parameter estimates when the source spectrum contains a harmonic line of constant frequency. A simplified Cramer-Rao lower bound analysis shows that the standard deviations in the estimates of the flight parameters can be reduced when IF measurements are used together with DOA measurements. Two flight parameter estimation algorithms that utilize both IF and DOA measurements are described and their performances are evaluated using both simulated data and real data. © 2017 Acoustical Society of America.
Sioutis C.,Defence Science and Technology Group
2016 Military Communications and Information Systems Conference, MilCIS 2016 - Proceedings | Year: 2016
This paper introduces a research program for investigating the technologies and challenges in achieving seamless integration between Defence's Tactical and Enterprise technology domains. The tactical technology domain encompasses the platforms, networks and supporting systems through which the Australian Defence Force (ADF) operates to achieve the commander's intent. Similarly, the enterprise technology domain encompasses the enabling business and information management aspects of the Defence organisation. Tactical to Enterprise Integration (TEI) is a complex problem which expands beyond simple network connectivity, or even information interoperability. There are many technical challenges and just as many potential solutions for achieving this integration. However, the operational effectiveness of the solutions varies depending on how they support the warfighter. With this in mind, the research program has four threads. Each thread is described in the context of a guiding warfighter vignette that depicts how a relevant tactical decision may be supported by the enterprise. Through preliminary research, the paper also identifies a number of key technology areas for initial investigation. © 2016 IEEE.
Richer T.J.,Defence Science and Technology Group
ACM International Conference Proceeding Series | Year: 2017
Any malware designed to be controlled by a remote sys- tem (as required for a botnet) must establish command and control (C&C) with that system. As part of establishing and maintaining C&C, botnet malware will often send regular messages to the locations of potential C&C servers, a practice known as beaconing. To avoid detection of these beacons, this traffic will be obfuscated and encrypted. Security researchers have had success with detecting beaconing by looking for traffic at regular time intervals, but malware authors are now introducing variation in these time intervals to foil this. Our research proposes that the regularity of both communication time intervals and data size are a useful feature set for detecting these C&C channels. To quantify the regularity of these streams of data, we use a nearest-neighbour estimate of entropy that is simple and quick to calculate. We then measure mean, standard deviation and entropy for time intervals and data sizes of a series of connections between a source and a destination. These features are then used as input to a support vector machine which is trained to detect botnet C&C activity. This approach was tested on the ISOT dataset|a dataset containing a mix of both benign and malicious real-world traffic. Using these features, we were able to train this classifier to accurately detect a large proportion of the botnet traffic.
News Article | October 27, 2016
The Cryogenic Sapphire Oscillator, or Sapphire Clock, has been enhanced by researchers from the University of Adelaide in South Australia to achieve near attosecond capability. The oscillator is 10-1000 times more stable than competing technology and allows users to take ultra-high precision measurements to improve the performance of electronic systems. Increased time precision is an integral part of radar technology and quantum computing, which have previously relied on the stability of quartz oscillators as well as atomic clocks such as the Hydrogen Maser. Atomic clocks are the gold-standard in time keeping for long-term stability over months and years. However, electronic systems need short-term stability over a second to control today's devices. The new Sapphire Clock has a short-term stability of better than 1x10-15, which is equivalent to only losing or gaining one second every 40 million years, 100 times better than commercial atomic clocks over a second. The original Sapphire Clock was developed by Professor Andre Luiten in 1989 in Western Australia before the team moved to South Australia to continue developing the device at the University of Adelaide. Lead researcher Martin O'Connor said the development group was in the process of modifying the device to meet the needs of various industries including defence, quantum computing and radio astronomy. The 100cm x 40cm x 40cm clock uses the natural resonance frequency of a synthetic sapphire crystal to maintain a steady oscillator signal. Associate Professor O'Connor said the machine could be reduced to 60 per cent of its size without losing much of its capability. "Our technology is so far ahead of the game, it is now the time to transfer it into a commercial product," he said. "We can now tailor the oscillator to the application of our customers by reducing its size, weight and power consumption but it is still beyond current electronic systems." The Sapphire Clock, also known as a microwave oscillator, has a 5 cm cylinder-shaped crystal that is cooled to -269C. Microwave radiation is constantly propagating around the crystal with a natural resonance. The concept was first discovered by Lord Rayleigh in 1878 when he could hear someone whispering far away on the other side of the church dome at St Paul's Cathedral. The clock then uses small probes to pick up the faint resonance and amplifies it back to produce a pure frequency with near attosecond performance. "An atomic clock uses an electronic transition between two energy levels of an atom as a frequency standard," Associate Professor O'Connor said. "The atomic clock is what is commonly used in GPS satellites and in other quantum computing and astronomy applications but our clock is set to disrupt these current applications." The lab-based version already has an existing customer in the Defence Science and Technology Group (DST Group) in Adelaide, but Associate Professor O'Connor said the research group was also looking for more clients and was in discussion with a number of different industry groups. The research group is taking part in the Commonwealth Scientific and Industrial Research Organisation's (CSIRO's) On Prime pre-accelerator program, which helps teams identify customer segments and build business plans. Commercial versions of the Sapphire Clock will be made available in 2017. Explore further: A new EU project on ultra-precise atomic clocks
News Article | February 15, 2017
The aircraft was on a scheduled flight from Kuala Lumpur to Beijing when it disappeared from air traffic controllers’ radar screens. Military radar continued to track the aircraft, which deviated from its planned route and eventually flew south, finally traveling beyond radar range. The aircraft was never seen or heard from again and the 242 people on board are assumed dead. The aircraft has never been found because nobody knows where it landed or crashed. The best guess is that it flew south for seven hours and then ditched in the Indian Ocean, some 1,800 kilometers southwest of Perth, Australia. But an extensive search of the sea surface and seafloor in that area has found nothing. All that raises an important question: have the authorities been looking in the right place? Today, Ian Holland of the Australian Defence Science and Technology Group publishes some of the reasoning that has defined the search area. Holland has been an important member of the team that has analyzed the data relating to the flight. In particular, he has focused on the last known signals sent from the aircraft to an orbiting Inmarsat communications satellite. In the absence of any other information from the plane, investigators have used these signals to determine the search area—but is there any more that can be gleaned from this data? First some background. MH370 was fitted with a satellite data unit capable of relaying voice conversations and routine data transmissions. It sent its information via an Inmarsat satellite that is geostationary over the Indian Ocean. Although the aircraft transmitted no voice communication, the satellite data unit continued to operate, acknowledging two telephone calls from the ground that went unanswered and making several routine broadcasts such as electronic handshakes and the like. At first glance, it’s hard to imagine how these brief data transmissions can provide any information about the aircraft’s location. But Holland and his colleagues have used them to gather a remarkable amount of information. The communications protocol requires a ground station to make contact with the aircraft’s satellite data unit at a specific time and frequency, regardless of where the plane is on the planet. However, the signal takes time to travel from the ground to the aircraft and back again. This time, known as the burst time offset, is determined by the distance the signal has to travel. This distance is straightforward to calculate. It defines a circle centered on the position on the ground directly below the satellite. However, the calculation does not suggest where on this circle the plane might be, and investigators have had to use other clues to narrow down this position. In total, MH370 sent seven signals from its satellite data unit, each defining a slightly different circle. It sent its final signal at 0019 UTC on March 8, 2014, having initiated a log on request just eight seconds earlier. That’s an important clue. Log on requests only occur when the satellite data unit restarts after some kind of shutdown. Investigators have assumed this shutdown occurred when the plane ran out of fuel and the SDU restarted using power from a device called a ram air turbine, which is deployed in an emergency to generate power. If that is correct, the last transmission must have been near the end of the flight. But how near? Could MH370 have glided many tens or hundreds of kilometers before it hit the ocean? If so, this significantly increases the potential search area. Holland says he and colleagues are able to narrow down this area using another line of mathematical investigation. The satellite data unit broadcasts at a specific frequency, but the aircraft’s velocity toward or away from the satellite introduces a Doppler shift that changes this frequency. This is known as the burst frequency offset. So in theory it’s possible that this shift in frequency can indicate the direction of flight at that instant. In practice, this calculation is hard to do and is much tougher than calculating the distance. Holland’s paper today is largely about this calculation. “The Burst Frequency Offset is a more complex measurement which is generally less well understood,” he says. The calculation is tough because of the number of variables that can influence the frequency. The aircraft’s motion is just one of them. The motion of the satellite plays a role, creating a Doppler shift associated with the uplink and downlink between the satellite and ground station. The ground station also attempts to compensate for any Doppler shift by changing the frequency. And the oscillators in the satellite and aircraft transmitters are not perfect. They vary, producing changes in broadcast frequency. Holland and co attempted to understand all these sources of frequency change by analyzing the broadcasts from MH370 during 20 previous flights in the week before it was lost. Holland goes on to show that if the plane was flying level when a call was made to the plane from the ground soon after contact was lost, then the burst frequency offsets suggest it must have been flying south. That’s important. He also shows that Doppler shifts on the final two broadcasts from the plane’s satellite data unit, suggest that it was descending rapidly. “The downwards acceleration over the 8 second interval between these two messages was found to be approximately 0.68g,” says Holland. This is consistent with the plane being out of control and out of fuel. That has important implications for the search area. If the plane was in an uncontrolled descent, it cannot have flown far after the last broadcast of the satellite data unit. And that means the plane must lie somewhere near the arc calculated from the burst timing offset data. “This suggests that 9M-MRO should lie relatively close to the 7th BTO arc,” concludes Holland. But exactly where on this arc isn’t clear. That’s interesting work which Holland is now opening up to outside scrutiny. He clearly sets out many of the assumptions he and his colleagues have had to make in coming to their conclusion. An important question for the community is whether these assumptions are all justified and whether Holland and his team have overlooked anything. In the meantime, the families of the victims are conducting their own search for wreckage associated with the plane. And until new evidence emerges, the search for MH370 will remain suspended. Ref: arxiv.org/abs/1702.02432: The Use of Burst Frequency Offsets in the Search for MH370
Hew P.C.,Defence Science and Technology Group
Theoretical Computer Science | Year: 2016
The Collatz function can be stated as 'for any odd positive integer x, calculate 3x +1and then divide by 2until the result is odd'. Colussi (2011) discovered and proved that if xattains 1 on the kth iteration of the Collatz function, then its binary representation can be written as the concatenation of strings sksk-1...s1where each shis a finite and contiguous extract from the representation of 1/3h. We provide an elementary confirmation of Colussi's finding, and comment on how working in binary 'protects' the repetends of 13has formed into eachsh. © 2016.
Taylor R.,Defence Science and Technology Group
Operations Research Letters | Year: 2016
For any given ϵ>0 we provide an algorithm for the Quadratic Knapsack Problem that has an approximation ratio within O(n2/5+ϵ) and a run time within O(n9/ϵ). © 2016 Published by Elsevier B.V. All rights reserved.
Weinberg G.V.,Defence Science and Technology Group
IEEE Signal Processing Letters | Year: 2016
Several independent investigations have demonstrated the validity of the Pareto distribution as a model for X-band high-resolution maritime surveillance radar intensity clutter returns. This has included validation of it for data collected from fixed costal surveillance radars, as well as airborne maritime surveillance radars. Consequently, there has been a steady development of radar detection schemes under such a clutter model assumption, both from a coherent and noncoherent detection perspective. One of the major initiatives at the Australian Defence Science and Technology Group has been to investigate the development of sliding window constant false alarm rate detectors for operation in a Pareto distributed clutter. A transformation approach has provided this capability, and one of the observations has been that a geometric mean detector, derived via this approach, tends to perform ideally when the number of clutter statistics in the clutter range profile is large. This letter examines this phenomenon and provides a mathematical explanation for it. © 2016 IEEE.