Large scale radar ornithology - Aarhus Universitet · 2011-11-29 · Large scale radar ornithology...
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1 21 January 2010 Large scale radar ornithology Large scale radar ornithology workshop "Trends in radar ornithology", Aarhus, Denmark Hans van Gasteren
Large scale radar ornithology - Aarhus Universitet · 2011-11-29 · Large scale radar ornithology 21 January 2010 6 Application of Doppler weather radars. NEXRAD example of mosaic
Large scale radar ornithologyworkshop "Trends in radar ornithology", Aarhus, DenmarkHans van Gasteren
Large scale radar ornithology
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ContentsHistorical overviewTypes of large scale radars used in ornithologyTechnical issues regarding radar coverageTrack-While-Scan image processing - introductionPros & cons with small scale radar
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Historical overview large scale radar• Migration across the southern North Sea
• Migration between the America’s• Nisbet & Drury 1964, 1967, Richardson 1976, 1978, 1979, 1982, Larkin 1980,
Williams & Williams 1977, 1978, Stoddard et al. 1983, Gauthreaux & Belser 1998a, b, 2005, Gauthreaux 1970, 1992
• Bird migration & flight safety• North America: DeFusco et al. 1986, Larkin 1994, Blokpoel 1969-1973• Europe: Buurma 1995, Buurma & Bruderer 1991, Ruhe 2005, 2008, Van Belle et
al. 2007, Shamoun-Baranes et al. 2008
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MIGRATION ACROSS THE SOUTHERN NORTH SEA Manly description of patterns seen in SE UK MIGRATION BETWEEN THE AMERICA’S Sea crossing from E-USA towards south-America, altitude, weather conditions at take-off, spring and autumn migration. Strategies & simulation BIRD MIGRATION & FLIGHT SAFETY Dominated by grey literature, (internal) reports and papers during proceedings Prediction of migration (Blokpoel, Van Belle) Last years finally scientific papers Other research topics with large scale radar were conducted in Israel (nocturnal migration as well as migration of large birds using thermals with respect to fly safety of Israel’s Air Force) REST ZIE BOEK NEWTON Typically large scale radars are used for large scale topics as sea crossings or barrier crossings in general and military low flying warnings.
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Large scale bird movements, 10-10-1980, Northern-Netherlands
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Application of surveillance radars
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Also air traffic control radars between america`s but this was hot in 1970’s / 80’s and is shift to NEXRAD & smaller radars by Gauthreaux Air defense radars mainly for flight safety in Germany, Denmark, Netherlands and Belgium
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Application of Doppler weather radars
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NEXRAD example of mosaic of reflection images. Clear difference between rain and birds/insects example lower left of reflectivity WITH Doppler. Examples of Velocity Azimuth Display (VAD) wind obtained from a volume measurement of a real wind (top) and a bird-contaminated (bottom) measurement. In both graphs the fitted line is a sum of sine curves, derived by Fourier series decomposition. Mean speed and direction are defined by the dotted lines.
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Detection range & cross section example for MPR at 10, 100 and 1000cm²
A number of technical notes regarding radar coverage MPR: 1,25MW beam, with detection probability (90%) up to 40 km (10cm2, single songbird), 70km (100cm2, Herring Gull) and 130km (1000cm2, flock). Note the minimum altitude for Herring Gulls to be detected at 80 km range: ~300m.
Note the altitude for a Herring Gull to be detected at 80km range by this coverage diagram: ~750m (~450m higher due to curvature of the earth).
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DEM, blocking obstacles, curved earth, elevation of the beam
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Note the “optimal” view in the northern half. However, due to the elevation of the beam, curvature of the earth and elevation of the terrain the minimum detection altitude in the southeast is on the ground. While in the “optimal” direction of the northern half the minimum detection altitude of the standardized measurement windows starts from 250m and higher!!!
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Resolution & pulsed volumes with birds or rain
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high res low res one low resolution radar cell
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Reflectivity products of the radar signal as detected by the ROBIN system in two resolutions. Left images shows the highest possible resolution, 30 m in range and 0.17 degrees, but over sampled by ROBIN, in azimuth. Decreasing resolution as is often done in post-processing weather radar products is shown on the right two images. Resolution is downscaled to 480 m range and 1.4 degrees azimuth. In the upper two panels an example of rain is shown in a 35 * 35 km square, in the lower two panels bird echoes are shown in a 16 * 16 km square. Calculation by Adriaan Dokter te show the radar reflectivity differences of moderate rain rate and strong bird migration. Moderate rain rate of 1 mm/hour reveals into an amount of 70.000 kg/km³. Strong bird migration in the order of 100 bird/km³ in only 5 kg/km³, assuming the average passerine can be approximated by a water sphere of 50ml.
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Processed signal with range
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Processed signal
Schematic A-scope (video) signal processingRaw signal, STC and CFAR with range
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STC
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Raw signal
Raw signal minus STC with range
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Raw signal - STC
Ingested bird
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False alarms
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From Wikipedia In the radar receiver the returning echoes are typically received by the antenna, amplified, down-converted and then passed through detector circuitry that extracts the envelope of the signal (known as the video signal). This video signal is proportional to the power of the received echo and comprises the wanted echo signal and the unwanted power from internal receiver noise and external clutter and interference. Sensitivity Time Control (STC) is used to attenuate the very strong signals returned from nearby ground clutter targets in the first few range gates of a Radar receiver. Without this signal attenuation, the receiver would routinely saturate due to the strong signals. Barton (1998): Sensitivity time control (STC) is a programmed variation in receiver gain designed to maintain constant echo signal strength as a target approaches the radar from some preset range. Constant false alarm rate (CFAR) detection refers to a common form of adaptive algorithm used in radar systems to detect target returns against a background of noise, clutter and interference. Other detection algorithms are not adaptive. Barton (1998): CONSTANT FALSE-ALARM RATE (CFAR) is “a property of threshold or gain control devices that maintain an approximately constant rate of false target detections when the noise, and/or clutter levels, and/or ECM (electronic countermeasures) into the detector are variable.” CFAR techniques are used in reception and signal processing to avoid increased false-alarm rates in the presence of jamming, clutter residue, or other interference sources.
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Processed signal with range, without clutter detection
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Processed signal w ith clutter
Schematic A-scope clutter mask (binary or dynamic)
Clutter
Processed signal with range
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Processed signalIngested bird
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Clutter (also termed ground clutter) is a form of radar signal contamination.
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Example PPI image processing Note bird echoes underneath binary clutter map
• X-, or S-band• ~10-25kW peak power up to 180kW for tracking radars• working ranges <5km• detailed local migration patterns• lower part of migration (0-2km)
