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Technology: Data delays leave satellite research up in the air

作者:山结棹    发布时间:2019-03-02 02:09:07    

By DANIEL CLERY The European Space Agency is not releasing enough of the data from ERS-1, its first Earth observation satellite, according to researchers who gathered last week to discuss the success of the project. ‘Data is beginning to flow, but it is still a bit of a trickle,’ says Alan Haskell of the Defence Research Agency’s Aerospace Division at Farnborough, where the meeting of the Remote Sensing Society took place. ‘It will become a flood . . . hopefully a well-managed flood.’ The ESA says that scientists underestimate the complexity of processing the data into a usable state. ERS-1 was launched by the ESA in July last year with a battery of instruments which produce images of the Earth’s surface day or night and through cloud. It can also calculate the speed and direction of both wind and waves, and detect the surface temperature of the oceans. The accuracy of these instruments has largely exceeded their designers’ expectations. The problem, according to Chris Rapley, head of the remote sensing group at University College London’s Mullard Space Science Laboratory, lies in the amount of time spent calibrating the instruments and delays in the data processing facilities back on Earth, known as the ground segment. ‘The ground segment was just not ready,’ Rapley says. Guy Duchossois, ERS-1’s mission manager, says that the ground segment is far more complex than for any previous satellite of this type. ERS-1’s main receiving station is in Norway, while the central processing and archiving centre is in Italy. There are other processing centres in Italy, Germany, Britain and France. Tuning the ground segment has been a learning process, Duchossois says, ‘but the scientists should be helping us to improve the system’. Duchossois has called a special meeting of all ERS-1’s affiliated scientists later this month to brief them and get their feedback on the project. Calibration of the instruments has been a mammoth task involving numerous ships and aircraft and hundreds of people. The largest calibration campaign was carried out by the ESA over three months last autumn off the coast of Norway near Trondheim. Three aircraft, three research ships and a network of 10 specially built buoys were on hand to measure the exact weather conditions and state of the oceans whenever the satellite passed overhead. In this way, data recorded on the surface can be compared with simultaneous readings from the satellite. Other calibration experiments have been carried out in the North Atlantic, the Mediterranean, the Gulf of Mexico and off the west coast of Canada. Researchers use the calibration data to find the best computer algorithms for converting readings from the satellite’s instruments into measurements of wind speed, wave height or temperature. This is particularly difficult with one of ERS-1’s instruments, the wind scatterometer, which looks at the roughness of the sea’s surface by bouncing microwaves off it to determine the speed and direction of the wind moving over it. Analysis of the instrument’s data gives two possible wind directions at any parti-cular point,

 

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