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Faq

Frequently Asked Questions

1. What's the sign convention of the line-of-sight data?

Summary:

  • In the timeseries/ folder, positive means motion toward the sensor, and negative means motion away from the sensor.
  • In the interferograms/ folder, the sign is flipped and positive phase means motion away from the sensor.

dolphin follows similar sign conventions to other InSAR software such as isce2 and MintPy. Inteferograms in dolphin are formed as reference_slc * conj(secondary_slc). The phase of the complex values in the interferograms/ folder indicates an increase in the line-of-sight (LOS) direction from the sensor, while a negative value indicates a decrease (motion towards the sensor).

After unwrapping, the sign convention is flipped and converted to meters (if the wavelength parameter is set) for the outputs in the timeseries folder. Assuming the wavelength parameter is set, the unwrapped phase is multiplied by \(-4\pi / \lambda\), so positive values in the timeseries rasters indicate motion toward the sensor, and negative values indicate motion away from the sensor. Thus, when combining two LOS rasters from ascending and descending geometries, postive values in both indicate that uplift is occurring.

Note that dolphin is able to process coregistered SLCs from arbitrary processing software, and does not always attempt to guess what sensor the SLCs are derived from. If the wavelength (within the input_options group) is not set in during configuration, the outputs in the timeseries folder will remain in radians, but keep the same sign convention (positive = motion toward the sensor).