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News  ERS-2 successfully targets China's Typhoon Matsa
Heavy rainfall and flooding from Typhoon Matsa killed at least 12 people and caused millions of euros worth of damage in China. In Matsa's aftermath, unique data from ESA's ERS-2 spacecraft reveal the interior wind fields powering it at its height. China's ninth typhoon this year, Matsa first came ashore at Yuhan County in Zhejiang Province on 6 August, with reported winds up to 250 kilometres per hour. Matsa brought heavy rains and serious damage to several coastal provinces and cities – in Zhejiang alone 13 000 houses were destroyed and farmland inundated.
Since downgraded to a tropical storm, Matsa reached Beijing on the evening of 8 August although failed to bring the torrential rainfall that was initially anticipated by the authorities - poised to evacuate thousands from vulnerable areas on the outskirts of the city.
ERS-2 instruments include a C-band scatterometer which works by sending a high-frequency radar pulse down to the ocean, then analysing the pattern of backscatter reflected back again. Scatterometers are particularly useful in measuring wind speed and direction at the sea surface, by detecting signature scatter from water ripples caused by wind.
Back in 2001 the spacecraft was struck a blow as the last of its pointing gyroscopes failed. However all instruments were still functioning perfectly, so ESA engineers worked with industry to develop a new 'gyro-less' working mode to resume data delivery.
Then in June 2003 the onboard Low Bit Rate data recorder failed, used to store non-radar image data when out of touch with ESA ground stations. However, recognising the value of this data, international ground stations responded by working voluntarily to collect and distribute ERS-2 results in near-real time.
ERS-2's scatterometer saw service interrupted between 2001 and 2003, due to degradation in the spacecraft's pointing control, but a new algorithm developed by the Belgian Royal Military Academy (RMA) returned it to operational status. This algorithm has been installed in the various cooperating ground stations.
Today, ERS-2 scatterometer data is employed by users worldwide, including the UK-based European Centre for Medium-Range Weather Forecasts (ECMWF), who routinely assimilate its results into their weather prediction models. ECMWF's remit includes the study of worldwide storms, so they have assimilated the Matua scatterometer results in their weather analysis for this time.
ERS-2 flies on the same orbit but half an hour behind ESA's ten-instrument Envisat environmental satellite, and so offers researchers a means to validate or supplement Envisat observations. Some ERS-2 instruments – its Synthetic Aperture Radar (SAR), Along Track Scanning Radiometer (ATSR) and its atmospheric Global Ozone Monitoring Experiment (GOME) – have counterparts on Envisat, although its scatterometer is unequalled for the time being.
To ensure continuity of C-band scatterometer coverage into the future, a more advanced scatterometer called ASCAT is payload of the payload for the ESA-built MetOp mission, due to launch in 2006.
Typhoon season A typhoon is the term for a tropical cyclone that occurs in the northwest Pacific or Indian Oceans west of the International Dateline. It is a large, powerful storm that rotates around a central area of extreme low pressure.
Typhoons arise in warm tropical waters that transfer their heat to the air. The warmed air rises rapidly, in the process creating an area of low pressure at the water surface. Winds begin rushing inwards and upwards around this low-pressure zone. Typhoons can form all-year-round in the waters off China, but the peak season comes between June and December.
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