Instead , only the magnitude of the velocity ( i.e. , the speed ) can be determined .
If the frequencies of the intersecting laser beams are the same then it is not possible to resolve the direction of the motion of the migrating particles .
Only the magnitude of the velocity ( i.e. , the speed ) can be determined .
If the frequencies of the intersecting laser beams are the same then it is not possible to resolve the direction of the motion of the migrating particles .