http://dspace.dsto.defence.gov.au/dspace The DSpace digital repository system captures, stores, indexes, preserves, and distributes digital research material. Search the Channel search http://dspace.dsto.defence.gov.au/dspace/simple-search http://hdl.handle.net/1947/9305 Title: JINDALEE Paper No. 134 - Project JINDALEE: the HF environment at Alice Springs, 1977-1978 <br/> <br/>Authors: Ward, B.D. <br/> <br/>Abstract: (U) This report is concerned with the HF radio environment at Alice Springs. It examines the background atmospheric noise levels, distribution of signals and their strengths, and availability of radar clear channels at Alice Springs during the Jindalee Stage A experimental program. Sat, 29 Oct 1983 22:58:59 GMT http://hdl.handle.net/1947/9304 Title: Optimisation of Surveillance Performance in Phased Array Radars. <br/> <br/>Authors: Alexopoulos, A. <br/> <br/>Abstract: Presented is an analytical approach to the study of the system-performance aspects of phased array radars using integro-differential tensor forms. Using tensor transformations between different coordi- nate systems we examine some of the most important system surveillance parameters for static and rotating phased array radars facilitated by an analysis on space-like and time-like manifolds. The mathematical approach discussed allows the derivation of the optimum configurations between the two types of arrays and a comparison between the two systems is made. Mon, 28 Apr 2008 22:58:59 GMT http://hdl.handle.net/1947/9303 Title: Modification of the Geographic Corrosivity Index and its Application to Overseas Bases. <br/> <br/>Authors: Bitcon, J.C.; Russo, S.G. <br/> <br/>Abstract: A Geographic Corrosivity Index (GCI) has been developed previously that models the atmospheric corrosivity at RAAF bases within Australia. Geographic, wind and other climate data are used to calculate the index for each base. The correlation of the GCI with atmospheric corrosion data from a large number of overseas bases, covering a broader range of geographic features and climatic conditions than experienced in Australia, was investigated to test its wider application. Modifications have been made to the GCI that enable it to be used with greater confidence for bases around the world that are within 200 km of the coast. Bases greater than 200 km from the coast have low corrosion rates, and a simpler algorithm based on time of wetness and distance from the coast was used to predict atmospheric corrosivity at these inland bases. Wed, 27 Feb 2008 22:58:59 GMT http://hdl.handle.net/1947/9302 Title: Benefits of Sharing Detections for Networked Track Initiation in Anti-Submarine Warfare. <br/> <br/>Authors: Fewell, M.P.; Thredgold, J.M.; Kershaw, D.J. <br/> <br/>Abstract: This report presents a quantitative study of a class of networking benefits in anti-submarine warfare. We show that sharing detections can produce an advantage over sharing only track-level information. We also indicate the conditions under which the advantage should be present, and estimate the magnitude of the advantage. This is achieved by focusing on the step of centralised track initiation, using metrics based mainly on sonar coverage area. We analyse multiple monostatic sonar, to give a concrete example aligned with current practice. The conclusions may be summarised in the statement that a 30% detection probability can be tactically useful, provided that there are other sonars with a similar Pd for the target concerned that are sharing information on detections. This result may provide a practical way around the great and continuing difficulty in obtaining acceptably high Pd values at tactically useful distances from a single sonar. Sat, 29 Dec 2007 22:58:59 GMT http://hdl.handle.net/1947/9301 Title: Proofs and Techniques Useful for Deriving the Kalman Filter. <br/> <br/>Authors: Koks, D. <br/> <br/>Abstract: This note is a tutorial in matrix manipulation and the normal distribution of statistics, concepts that are important for deriving and analysing the Kalman Filter, a basic tool of signal processing. We focus on the proof of the well-known fact that the sum of two n-dimensional normal probability density functions is also normal. While this theorem is usually taken for granted in the signal processing field, proving it provides an insightful excursion into techniques such as Gaussian integrals and the Matrix Inversion Lemma. Tue, 29 Jan 2008 22:58:59 GMT http://hdl.handle.net/1947/9300 Title: Novel concepts for Conformal Load-bearing Antenna Structure. <br/> <br/>Authors: Callus, P.J. <br/> <br/>Abstract: This report describes the activities undertaken by the author during his Defence Science Fellowship on the topic of Conformal Load-bearing Antenna Structure (CLAS) at the Air Force Research Laboratory, Air Vehicles Directorate, Structures Division, Advanced Structural Concepts Branch (AFRL/VASA), Multifunctional Structures Team at the Wright Patterson Air Force Base, Ohio, USA, from June 2006 to August 2007. The aim of CLAS is to enhance the performance and capability of air vehicles by integrating antennas into the load-bearing airframe structure. The author and AFRL/VASA team devised new CLAS concepts and selected one, Slotted Waveguide Antenna Stiffened Structure (SWASS), for further evaluation. In SWASS the top-hat cross-section stiffeners on thin skins or blade stiffeners in sandwich panels would serve the dual purpose of acting both as structural stiffeners and as slotted waveguide antennas. This concept was partially validated by modelling, design, manufacture and testing at the coupon level. Waveguides were manufactured from carbon fibre reinforced plastic and their insertion loss measured. Conventional AS4/3501-6 prepreg tape waveguides exhibited the lowest losses and, although these losses were well above those for metallic waveguides, they were expected to be acceptable for first generation SWASS antennas. Work is continuing to complete the validation. Tue, 29 Jan 2008 22:58:59 GMT http://hdl.handle.net/1947/9299 Title: JINDALEE Paper No. 130 - An evaluation of the performance of the JINDALEE Stage A surveillance receiver <br/> <br/>Authors: Earl, G.F.; Garrett, R.E.; Ward, B.D. <br/> <br/>Abstract: The performance of the Jindalee Stage A surveillance receiver is evaluated using the HF spectral data recorded during the period October 1977 to September 1978. Tue, 29 May 1979 22:58:59 GMT http://hdl.handle.net/1947/9298 Title: Speaker Localisation using Time Difference of Arrival. <br/> <br/>Authors: Thai, D.Z.; Trinkle, M.; Hashemi-Sakhtsari, A.; Pattison, T. <br/> <br/>Abstract: This report describes the research and development of speaker localisation to locate the position of a person speaking. Two closed-form localisation techniques were analysed, the first was developed by Schau and Robinson (1987) based on spherical intersection and the other developed by Chan and Ho (1994). Both techniques are based on time difference of arrival measurements. Accordingly three time delay estimators, namely cross-correlation, generalised cross-correlation, and an eigenvalue decomposition based algorithm were analysed. The implementation of the algorithms in Matlab and the results from the analyses are discussed. Sat, 29 Mar 2008 22:58:59 GMT http://hdl.handle.net/1947/9297 Title: Structural Health Monitoring of a Bonded Composite Patch Repair on a Fatigue-Cracked F-111C Wing. <br/> <br/>Authors: Baker, A. <br/> <br/>Abstract: A large fatigue crack in the wing skin of an Australian Defence Force F-111C aircraft was repaired with an adhesively bonded boron/epoxy fibre composite patch. The patch prevented further growth of the crack for 670 flying hours. To aid in the continued safe operation of ADF F-111 aircraft, a decision was later made to assess the residual life of the F-111 wings in part by undertaking a fatigue test at DSTO on a retired wing. An additional aim of the test was to substantiate further the bonded repair, in view of its potential application to other F-111 aircraft – either as a repair for cracked wings or as reinforcement to inhibit fatigue crack formation in uncracked wings. The test importantly would also evaluate the effectiveness of non-destructive inspection (NDI) and other non-destructive procedures to detect crack growth under the patch or disbonding of the patch system. The repaired wing was therefore selected and used for this study. In this test the patch was successful in preventing growth of the crack for around a further 9000 simulated flying hours. As a consequence of NDI indications of local patch disbonding and concern that it could lead to rapid growth of the repaired crack and thus premature failure of the wing a structural health monitoring (SHM) technique was implemented to monitor the patch. This report, after providing background to the repair and its performance, describes a) the comparison of NDI results for crack detection with the fractographic studies on the crack after the tear down and b) the comparison of the NDI and SHM results for disbonding with bond-strength measurements on the patch system undertaken at the completion of the fatigue test. Both NDI using an ultrasonic technique and the SHM using a strain-based technique were successful in detecting disbonding of the patch. Based on the use of the bond-strength test as a destructive validation procedure it was concluded that both the NDI and the SHM techniques were highly effective in detecting disbonds and that the strain-based SHM technique (with several significant improvements) could be used for in-flight monitoring of repair patches in demanding or critical applications. Wed, 27 Feb 2008 22:58:59 GMT http://hdl.handle.net/1947/9296 Title: JINDALEE Paper No. 123 - Computer control of the JINDALEE Stage A HF transmitting station <br/> <br/>Authors: Forbes, A.M. <br/> <br/>Abstract: Between 1976 and 1978, the JINDALEE experimental over-the-horizon radar in Central Australia has had an HF radio transmitting station controlled by a PDP11/10 minicomputer, using a specially developed program written in the MACRO-11 assembly language. This paper shows how the design and maintenance of the program were influenced by the available facilities, and goes on to describe the computer control that was developed. A recommendation is made that computer installations at remote sites should be selfsufficient in programming aids. Mon, 29 Jan 1979 22:58:59 GMT