Space radar seeks out lost cities beneath the sand: Nasa's dollars 366m laboratory is gathering data on ancient civilisations and declining forests. Steve Connor reports

AN ambitious attempt to map the changing face of the Earth with a radar in space that is powerful enough to reveal signs of lost civilisations buried under desert sands reached its half-way stage yesterday.

Astronauts on board the space shuttle Endeavour have had little to do but look out of the spacecraft's windows as their on-board radar automatically gathers a databank equivalent in size to about 20,000 encyclopaedias. It will take scientists up to a year to analyse the information.

The National Aeronautics and Space Administration (Nasa) said that after five days of scanning the surface of the Earth, the radar equipment in the shuttle's cargo bay was meeting the 'highest expectations' of scientists researching topics ranging from tropical forest destruction to ancient history.

One of the most exciting projects will be to study the radar images around the supposed site of the city of Ubar in the Arabian desert, which was once the centre of the ancient frankincense trade. The radar can reveal solid structures buried in several metres of dry sand and could prove invaluable in future archaeological excavations.

As the shuttle flew over the Gulf yesterday, the radar scanned southern Oman in the hope of imaging the lost city. It could be some time, however, before scientists are able to decipher any ancient structures.

A team of British scientists is taking part in the huge effort to calibrate and analyse the wealth of data the radar equipment on the shuttle is gathering. Gordon Keyte, a scientist with the government-owned Defence Research Agency, said: 'The bulk of the mission is trying to manage the resources of the Earth much better. It's all aimed at understanding our life on the planet.'

Endeavour is carrying in its cargo bay the dollars 366m ( pounds 249m) Space Radar Laboratory - built by the US, Germany and Italy - which Nasa says is the most sophisticated radar used by non-military scientists.

Since the launch of the shuttle on Sunday morning its six astronauts have watched as the radar mapped rice paddies in Japan, geological features in the Andes and crops growing on the prairies of Oklahoma and Wyoming. They even found time yesterday to radio Russian cosmonauts on board the Mir space station as the two spacecraft flew within 1,300 miles of each other.

Radar can take perfect images regardless of weather or sunlight conditions. Radar waves penetrate clouds and under certain conditions can see through vegetation, ice and sand. 'In many cases, radar is the only way scientists can explore inaccessible regions of the Earth's surface,' Nasa said.

The American space agency has in recent years responded to criticism that it has spent too much money on expensive projects that bring little relief to the problems of the world by initiating its 'mission to planet Earth', a programme aimed at understanding human-induced changes in the environment. The Endeavour's mission to produce a detailed radar map of the globe is an important part of this.

Subjects that the shuttle radar will shed light on include:

The ecology of life on Earth, especially the tropical rainforests of the Amazon and the temperate forests of North America and central Europe. The radar can assess the number of tree trunks in a given area and so monitor forest destruction.

How water circulates on land and the factors that give rise to droughts and desertif ication. The shuttle's radar will assess the 'hidden' water stored as soil moisture, which is often the crucial factor in determining whether a region will succumb to drought. Computer models based on the data will help to predict a region's susceptibility to water shortages.

The behaviour of volcanoes will be studied as they erupt. Nasa scientists are confident that the radar will manage to fly over one in the process of erupting. Such information will be invaluable in assessing the impact of volcanic activity on the Earth's climate.

Dr Keyte and the rest of the British team are taking part in an experiment to calibrate the shuttle's radar using a field of aluminium reflectors set in a field at Feltwell in Norfolk.

As the shuttle flies overhead, scientists are measuring soil moisture levels in the fields to produce accurate assessments of the relationship between water levels in the soil and the strength of radar images.

Dr Keyte said farmers and agricultural economists should in future be able to assess future crop yields by estimating soil moisture and plant growth with the help of radars in space. 'Clearly there is a tremendous economic potential although at the moment it is difficult to predict just how this information will be used.'

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