It is not published yet but you can do these steps in any gis. His TanDEM-X data had precise orbits but there was still a ramp indicating that there is a wrong angle estimated between both acquisitions.
Yes, there is an incident_angle band in Tie-point grids. When you perform Range-Doppler you can create Projected and Local incidence angle bands from it. I used local incidence angle for my map because this band seems less general and more informative for me than other possible incident bands. In my opinion, using incident angle before Range Doppler if everything will go smoothly, may and should produce the same (or comparable) result, because here we are dealing with just mathband calculations, not with the tricky SAR operations. I’ll check it in my spare time.
I’ve checked it. When I calculated Step1 before Range-Doppler using Incidence angle from tie-point, I received blank band. So, it would be better to work according to the workflow above.
Interesting… I carried out the band-math UnwPhase to displacement calculation with the tie-point-grid incidence angle band before terrain correcting and after and it produced the same result. Also results were very close to each other when using the projected, local, or ellipsoid-derived incidence angle. Oddly enough the results are strikingly different from the ones obtained using SNAP’s Phase To Displacement operator. Does anyone have an idea what kind of expression the operator uses? I was unable to find the answer in the SNAP documentation.
Sorry, I’m going to as a silly question. After all the exhausting work I’d done, I lost understanding - why do we have some value (not equals to zero) in a point where we assume elevation hasn’t changed? Where points 3 and 4 come from, what is the reason for their existing?
the unwrapped interferogram simply shows you the difference in distance to the sensor between image 1 and image 2. It has no reference yet. But at some point, the change should be zero (given that not the whole surface covered by your scene is sinking). You need to tell SNAP where this surface of change touches the ground.
Oh, cool!!! Thanks for your answer!!!
I found that differences between altitudes of a satellite at the moments of sensing the images were from 1.5 to 12 meters. But my points which didn’t change the elevation, have values about -200 millimeters. I am interested, how could it be.
if you are not familiar with the AOI, what is the best way to identify a reference point?
where can I apply " the reference height"?
you can subtract it from your raster in the band maths
I want to mask out zero displacement area from this image.
Please guide how to do it?
Very nice map!
I would export it to GIS and mask out the values equal to zero. You could also make it in a more complicated way: export all the values from your region of interest to Excel, create a point shape-file for points with zero displacement, import the shape-file back. It should cover all the points of zero displacement.
i wish no change values to remain transparent and only displacement values to be visible.
In displacement map no displacement values are being displayed in white. When i play with transparency, other colors also loose their sharpness.
go to the color manipulation tab and switch to the table coloring. There you can define value ranges and assign colors (also transparent ones) to the different ranges.
Positive means subsidence and negative signifies uplifting?
I have done the following steps to build maps of Uplifting and subsidence (map of displacement)
After completing the steps above, we performed the following steps:
1- Exporting data for SNAPHU processing
2-Importing results from SNAPHU processing
3- Phase to Displacement By Operator
4- Create Stack (Coherence + Displacement)
5- Geocoding(Range Doppler Terrain Correction Operator)+Elevation
6- By Band Maths: Made DisUP35Coh & DisUP50Coh (Map of displacement that Coherence upper 0.35 and 0.50):
if (coh_IW3_VV_22Sep2016_31Aug2018 > 0.35) then (displacement_slv1_22Sep2016_VV) else (NaN)
Track is Descending and other properties are:
Now ,The question is: what is the positive and the negative in these maps?
Positive = Subsidence ?
Negative = uplift?
DisUP60Coh-Garmsar.kmz (2.4 MB)
Thank in advance
that depends on the date of your master and slave image. The difference indicates the change between both dates. But note that the map only displays the change along the line of sight, not absolute vertical displacement.
- Difference between vertical and LOS displacement
- Vertical displacement senitnel 1 interpretation
- Vertical and horizontal displacement
- The phase shift originates from horizontal or vertical displacements
Does the pattern make sense to you?
Very thanks ABraun
I have read the above, but this question remains for me!
I got the old image as masters and newer image as slave .
the phase and Coh are
IF phase converted to displacements and track be descending , the positive signal is uplifting or subsidence?
I am processing Landslide data but through DInSAR but couldnot found any reliable results.(Landslide events dated 13 Aug 2017 and 29 june 2018) at different sites with AOI in the same swath IW2 of Sentinel 1A images.
Wish to process a fresh from start. Would you please guide me if i share my location with you?
Like data acquisition, base line guidance, processing parameters and other related help.
sorry, I can’t grant to keep track of every step. What about the comments on your questions in other topics?
There are answers to almost any question in this forum:
- general workflow: Interferogram Formation - Subtract topographic phase check box
- full tutorial on subsidence monitoring: https://eo-college.org/resources/insar_deformation/
- notes on image selection and constraints: How can we calculate the volume of displaced material with displacement band(displacement_VV)?
- atmospheric disturbance: Subsidence Map
- InSAR - A practical approach: Have a look the comment on landslides in chapter 4.1.4
Because of the constraints (topography, surface change, atmosphere, long temporal baseline), many studies favor PS InSAR for landslide analysis:
If they leave any questions, feel free to ask.