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Australia gets new advanced weather radar, courtesy of the Bureau of Meteorology . . . Bringing you much more than pretty pictures! I first noticed this giant “golf ball” last year, sitting high on its “tee”, right next to the Terrey Hills golf driving range in Sydney’s north. “Surely,” I thought, “that’s not just an advert for the driving range . . .” No it’s not (although I bet they are very grateful!) – it’s much more interesting than that – it’s the latest in the Bureau of Meteorology weather radar upgrades! And the best part: you can view its images via the ’net. by Ross Tester www.siliconchip.com.au www.siliconchip.com.au siliconchip.com.au JJanuary anuary 2010  21 2010  21 A typical PC “radar” screen showing approaching rainfall. You can add a lot more map features if you wish. W eather forecasting around Australia has become even more accurate and precise with the opening of several new highresolution Doppler weather radar installations. With the newest at Laverton (Vic), Mt Stapylton (Brisbane, Qld) and now at Terrey Hills in Sydney’s north, each has already proved their $4 million price tags money well spent. You can become your own weather forecaster by following the weather radar images on the Bureau of Meteorology’s website. The images from the newest technology weather radars cover the last half hour with screens six minutes apart. Older radars have images 10 minutes apart. There’s always a lag of up to about eight minutes – you can look out the window and see that it’s raining where you are when the screen tells you that the rain is still approaching (and vice versa). That’s mainly because of the incredible amount of computer “number crunching” then the upload times to the net. You can also show the whole of Australia with clouds and rain interpolated from all other radar sites. You get the choice of 64, 128 and 256km range, plus a 512km “composite” interpolated from other radars. You can also enable or disable a variety of map features, such as locations, roads, topography, etc. Rainfall is colour-coded by intensity – my experience is that anything yellow or above is getting rather heavy! You can log on to the Bureau’s website (www.bom.gov.au) and follow the prompts – the Terrey Hills radar images, for example, are at www.bom.gov. au/products/IDR714.loop.shtml#skip. But there’s a lot more than just radar images to look at. The Bureau has a vast array of tools to help the average person understand what the images represent and how to use them. The Terrey Hills radar Completed in April last year and commissioned after extensive testing on September 9, it is the fifth of six new high resolution weather radars to come online around the country thanks to the Federal Government’s $62.2 million radar upgrade project. In fact, the Government has extended the program with another four high resolution weather radars to be installed as part of the upgrade program. As far as Sydney is concerned, the Terrey Hills installation effectively replaces the Appin (south of Sydney) weather radar which has been operating since 1992. As well has having double the resolution of the Appin radar, Terrey Hills also has Doppler capability, which allows the display of wind flows associated with weather systems as well as rainfall intensity. Another problem for the Appin radar was/is that is considered too high above sea level to properly detect lowlevel rainfall over the Sydney area (as you can see by comparing the images from Appin and Terrey Hills at the same time). The Appin Radar will continue to operate in the short term. The Bureau is currently examining sites to the south of Sydney for a planned new Wollongong radar. On-going operational benefits of the Terrey Hills weather radar will include: • Improved short-term forecasts and The Moving Storm: Monday, November 30 2009 22  Silicon Chip www.siliconchip.com.au siliconchip.com.au Left: it’s not rain – how those on the ground wished it was – these radar images from Melbourne (Laverton) at 09.00 UTC (8pm EDT) on 7 February last year, at the height of the Victorian bushfires, where smoke was dense enough to show up. Right: the colour-code located underneath each map/image refers to the rainfall intensite. Here’s the key – and while it’s not absolutely accurate, it’s not too bad, either. I’ve only seen dark brown once – and that was a day that Sydney would rather forget! warnings of severe weather, including hail, damaging winds and tornadoes • Improved radar-derived rainfall rates for use in flood warning applications • Improved short-term forecasts of rainfall • Enhanced tracking of the movement and strength of wind changes such as southerly busters, cold fronts and sea breezes. Because the newest weather radars are Doppler, they can be used to measure speed – of wind, of storm fronts, and so on. Weather radars don’t reflect off clouds (the droplets are too small) but they reflect off the raindrops those clouds produce. Unfortunately, they also sometimes reflect off birds and insects, aircraft and even bats taking to they sky at dusk! Radar close to the coast may also reflect off shipping. The newest site The radar site at Terrey Hills (33.701°S, 151.210°E) is 195m above sea level and is approximately 18km north of the Sydney CBD. The radar covers more than a quarter of Australia’s population. Based on detecting echoes at a height of 3000m, the radar has an unobstructed view to the north, south and east. However, the rough topography of the Great Dividing Range slightly compromises the radar’s view to the west. Even so, high-level (ie upper-atmosphere storm) range extends west to Mudgee and Bathurst, as far north as Bulahdelah and Scone (in the Hunter Valley), and south to Goulburn and Ulladulla (NSW south coast). An examination of the coverage map will show that these limits overlap the coverage area of other weather radars in the system – which of course is part of the overall Bureau of Meteorology design. The heart of the installation at Terrey Hills is a Meteor 1500S dedicated S-Band Doppler weather radar, manufactured by AMS-Gematronik. It operates in the 2.8GHz band with a peak power of 750kW. The 8.5m linear horizontallypolarised dish has a gain of 45dB, 1° half- power beam width and 26dB side lobe suppression. It can scan between 0.2 and 6rpm but normally, the Terrey Hills scan rate is set at 3rpm. It is accurate to 0.1° and is mounted inside the protective fibreglass “radome”. The radar transmitter features a fully solid-state modulator which drives the VKS 8387 klystron tube. The klystron system, together with a coherent receiver, offers up to 20dB improvement in stability and clutter suppression compared to older, coaxial magnetrons. Other advantages of the klystron transmitter included high average and peak power, high gain, high efficiency, longer pulse duration and sufficient control of the waveform and frequency. The “Golf Tee” tower The 20m tower, which weighs in at about 60 tonnes, is made up of a bolt cage foundation, base, column, conical sections, a radar “floor” and topped by a 11m diameter fibreglass radome. The tower itself is 3.8m in diameter and the conical section at the top is 7.2m in diameter. It was manufactured by Melbourne- As a storm, it was only a tiddler. The colours show the rain rate – only a few patches of red, mostly greens, blues and greys. This half-hour “loop” from 04:18 to 04:48 UTC (3:18 to 3:48pm Sydney time) tracks the path of rain across the city. This one is also slow-moving: storms often move right through the area and out to sea in that 30-minute timeframe. www.siliconchip.com.au siliconchip.com.au January 2010  23 Remember Tropical Cyclone Larry, which brought so much devestation to North Queensland in March, 2006 (who could forget the price of bananas). Here Larry is being tracked by the Townsville weather radar (265km away) as it develops out in the Coral Sea and then finally comes ashore right over Innisfail. One surprising aspect of these radar images is the lack of rain intensity – not much above moderate. But if you’ve ever been caught in a cyclone, you’ll know it’s a tad more! based Eliot Engineering, who also manufactured the towers at Melbourne and Brisbane. How it works Contrary to what you might expect (having seen radar at airports, etc), as well as spinning in the horizontal direction weather radar antennas also move in the vertical direction. From a minimum of 0.5° above the horizontal, each rotation of the “dish” increases by 0.5° to build up a “3D” image. If this wasn’t done, the radar image would effectively be at one particular elevation. And as we all know, rain clouds/storms don’t scud along at a single convenient height. Depending on the type of cloud or storm it could be anywhere from virtual ground level right up to tens of thousands of metres. Hence the dish moves to capture the various heights. The hardware and software to control this is quite low level – in fact, a standard 512MB 2GHz PC is used running proprietary “Ravis 1500” software. Radar images are first processed on site by “Aspen DRX” signal processor software. There is an enormous amount of information contained in the reflected radar images. For example, there’s always clutter and false images which need to be analysed and if possible eliminated (although that’s not always practical). And of course, there is the integration of the various radar sweeps to form a single, coherent image. All this requires significant computer grunt, not to mention some pretty smart software. As a standard tool for the meteorological user, AMS - Gematronik has developed a powerful and versatile software package, fittingly enough Joining the two sections involved lining up the bolt holes. November 2008: The first 5m tower section in place 24  Silicon Chip Lowering the 5m pedestal that allows the radar dish to rotate. siliconchip.com.au It’s important that the radar site has an unobstructed view. This semi-fisheye shot is looking towards the west. called “Rainbow”. This offers the integration, processing and distribution of any kind of meteorological data and for remote control of weather radars within a meteorological network. Warnings While duty forecasters will always be monitoring their screens at the various meteorological offices (each capital city), much of the information coming in can trigger warnings which the duty forecasters can then act upon – for example, issue warnings to the media regarding approaching storms, prepare for possible floods, and so on. The duty forecasters’ screens will contain a lot more information than radar images but radar is a very important tool in getting the message out to the public about short-term weather. The highly-skilled operators can identify a lot of varied information February 2009: Installing the 8.5m radar dish onto the pedestal. siliconchip.com.au from weather radar that the untrained person would probably miss completely – for instance, southerly busters (very common in Sydney in summer), differences in thunderstorm types, hail, rotational super-cells. While the various BOM weather radar websites are very popular at the best of times, during storms or other weather events usage shoots up virtually exponentially. Thunderstorm warnings, for example, not only use the information from the weather radars (and other measuring equipment, some at the weather radar site but also located right across the country) and are automatically plotted on maps on the BOM website, with expected direction and intensity. The software tracks the thunderstorm on radar for a couple of cycles then projects its likely track. Even the place names are automati- cally generated and displayed so there can be no doubt in viewer’s minds as to location. Again, all this information can be circulated to the mass media for public warnings. Lightning One thing that radar does not detect is lightning, basically because there is nothing to reflect the beam back. However, there are quite precise methods of measuring lightning strike location and intensity but these are not functions the bureau performs. Instead, private organisations provide this service either in real time or as a delayed report. Lightning strike measurement is a fascinating subject in itself – SILICON CHIP has featured a couple of articles on the subject, the latest being in the November 1996 issue (“LPATS – StrikSC ing a Blow Against Lightning”). March 2009: Placing the last of the radome panels. January 2010  25