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Aisling Irwin reports from the annual meeting of the American Association for the Advancement of Science in Atlanta. An American academic says she was asked by the Los Angeles police department this month whether a satellite might have passed at the right time over the house where O. J. Simpson's wife was murdered and thus be a source of evidence about the crime.

The case highlights the enormous potential of earth observation techniques for monitoring (and predicting) human behaviour - and the accompanying problems of assault on privacy, according to Bruce Marks, lawyer at Jurisat Inc., a firm set up to examine the issues.

Joanne Grabynowiz, a professor of law at North Dakota University, said that the LA police had also asked her about the legal problems of using such information in court.

Although satellites could not produce such data at present, Mr Marks said that this will change, leading to re-evaluation of definitions of privacy and private property. "Within a few years the LAPD might have this capability." Remote sensing techniques will lead to the ordinary person being "able to monitor your next door neighbour late at night".

The question of whether satellite imagery will be acceptable as court evidence urgently needs addressing, both from the point of view of the quality of the data and the question of whether its use is an invasion of privacy, he said.

Privacy may be a problem with techniques which are not passive, such as radar. "A satellite sensor which transmits energy into an object from which it is deriving an image. A series of cases makes it clear that a trespass claim would probably be valid where there has been the conversion of something of value combined with the penetration of someone's property."