1. A method of calibrating seismic data, the method comprising: receiving traces from a seismic survey that covers a volume; determining a pair of seismic attributes for each of a plurality of positions within the volume (“survey pairs”); deriving a pair of seismic attributes for each of said plurality of positions from a source independent of the survey (“independent pairs”); calculating a rotation angle and one or more scale factors that calibrate the survey pairs relative to the independent pairs; and calibrating the traces with the rotation angle and the one or more scale factors.