Using the formula is the traditional way but you can as well use the “phase to displacement” module.
You have to note three things:
- the displacement derived from the formula is a relative measure. It simply adds up the phase increase/decrease and converts it into metric units (if you enter the wavelength in mm you get the displacement in mm). You have to find a ‘zero displacement point’ in your area and calculate the remaining change from that. Explained here: Subsidence map in 3d view
- The displacement is not in vertical direction alone but along the line of sight (LOS) between each pixel and the sensor. So you have to consider the slant looking geometry of the SAR sensor.
- unwrapping works best if you have large connected areas of high coherence. The phase fringes are then added together to convert the circular measure to an absolute. But if, as in your case, high coherence is only available in small enclosed areas, the unrwapping/displacement values cannot be compared throughout the full image (e.g. from left to right) because the phase only gets randomly added up without being represented by the real phase information.