@johngan Using the formula for calculating the displacement in LOS you provided in your first post I obtained strange results. Using unwrapped phase in the range -37 to 18 the calculated displacement is quite different compared to the displacement obtained with the SNAP function . Any idea?
I imagine you are referring to the following equation: (phase * wavelength) / (-4 * PI)
When you use SNAP tool for deriving LOS displacement, the units are in meters. Hence, if you want to get exactly the same numbers in LOS with that of SNAP, when using the equation make sure that the units in wavelength are in meters. If you enter the units in cm, the results will be in cm.
Using either the equation or the SNAP toolbox the results should be the same
The values for the equation are the following:
(unwrapped phase * 0.056) / (-4 * PI).
the results will give you LOS displacement in meters just like SNAP
Wavelength depends on the sensor, you can find it with Google. You can also look up the radar frequency from the abstracted metadata and compute wavelength = speed of light/frequency.
Sorry for rising up this post, but I checked with both formulas above. The displacement is fine, but with the vertical one calculated with formula provided (unwrapped phase * wavelength) / (-4 * PI * rad(cos(incidence angle)) )the result is not as expected (see below). The incidence angle is taken from the tie-point grid band incident_angle.
Any suggestions?
24h latter - resolved using the average of the LIA from incident_angle band .
In SNAP after clicking menu item ‘radar>interferometric>unwrapping>snaphuImport’ there will be a box with 4 tabs ‘read’, ‘read unwrapped phase’, snaphuImport’ and ‘write’. But in GraphBuilder’s window after adding the same item as an icon there are only 2 tabs, ‘read’ and ‘snaphuImport’. I can add a ‘write’ tab but can not find the item corresponding to ‘read unwrapped phase’ tab. Is it available in SNAP?
ohhaha, well forget for the easiest step tbh i used the ‘phase to displacement’ at my first try, the processing parameters window didn’t show anything, is there any alternative?