SAR interferometry is an advanced version of this technology. It involves scanning an area from two different antenna positions. The principle remotely resembles the way in which humans see with two eyes. For points at various elevations, various path length differences result. Ultimately, we obtain a phase-difference pattern called an interferogram. Having further refined this technique, DLR scientists have evaluated the back-scatter from more than four million permanent scatterers in numerous images. This method permits detecting elevation changes in the centimetre range.