The Swathbuckler international collaboration task between government laboratories of US, Canada, UK and Australia has jointly implemented an affordable, experimental, real-time, wide-swath SAR imaging radar system. This paper is one of a coordinated collection of papers submitted by the collaboration partners. It describes the radar processing frontend component of Swathbuckler, responsible for the intelligent interface between SAR radar and the high-performance computing cluster. The unique requirements of this program, namely the real-time processing of SAR swaths encompassing 250,000 range samples, dictated a novel reconfigurable FPGA architecture for this interface. The associated firmware performs high-speed digitisation, digital down-conversion and distribution to each of the nodes in the computing cluster. The design has evolved from early attempts to develop a custom prototype through to an integrated solution using commercially available hardware. The interface has successfully flown in Swathbuckler flights supporting wideswath, high resolution SAR processing at a sustained 500Hz pulse repetition frequency. The work has demonstrated that it is possible, with currently available and technology, to provide an affordable, compact means of managing unprecedented SAR swath sizes in an airborne platform.
A number of X-band radar data collection exercises have been conducted in the area of the South Falls sandbank, which were supported by two deployments with a research vessel that directly measured the tidal flow and water depth. Results from a total of 12 low grazing angle airborne radar data collections are presented. Nine sorties were flown with the Enhanced Surveillance Radar, using a synthetic aperture radar (SAR) mode. The other three aircraft sorties were flown using a real aperture scanning radar mode. For the scanning radar experiment, data were collected from around the sandbank on three successive days with grazing angles of 0.5u-4u. The wind speed remained relatively constant at 7-9 m s 21 during this experiment. The radar cross-section modulation was found to have a linear relationship with the estimated surface strain rate, and the constant of proportionality was found to be 500 s when the radar was pointing downwind or crosswind, and around 200 s when looking upwind. For the SAR mode data collection, a similar look-direction dependence was observed as the scanning mode data, and a strong wind speed dependence on the visibility of the sandbank was also seen. At 6u grazing angle and a peak strain rate of 5610 24 s 21 , the strength of the radar contrast decreased by approximately 1.7 dB for unit increase in the wind speed, and the radar contrast vanished for wind speeds much beyond 10 m s 21 .
Two types of cast steel rail bogies have been affected by cracking and defects. The cast steel design was from a period when bogie loads were lower than the endurance limit. However, the bogies as manufactured included a large number of casting defects and 60 years of operations has resulted in many repairs being applied. Thus like all ageing structure, the original basis for safe operations may be invalid. Structural assurance instructions were developed based on the following work. A condition data survey was undertaken to obtain configurations and defects within the fleet. This was used to assist in identifying critical areas, types and shapes of defects. Two bogies were instrumented to obtain operational loads that were compared to modern standards to provide both a spectrum for future operations and loads for Finite Element Analysis (FEA), Fatigue and Damage Tolerance Assessment (DTA). Finite Element Models (FEM) were developed to provide internal bogie loads and stresses for use in the fatigue and DTA and identify additional critical locations not identified in the condition data survey. DTA were undertaken to determine maximum flaw sizes and to verify the safe period of operation; given the loads, usage and stress data of the previous tasks. Based on the work undertaken, instructions for continued management documenting acceptable flaw criteria, life limits, and ongoing inspections were provided.
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