# Selecting the Stamps PSI reference Points

I have analyzed a coastal area with stamps. There is major evidence in there and also all the area has a yearly settlement. I have to choose to select a reference point in this area. I highly need your help with the location of the reference point and radius. Is it possible to select close to the major evidence or in the far areas with the yearly settlement? And what about the radios of the reference point in Stamps PSI.
Regards,

You can select the radius while plotting the velocity plot (ps_plot(‘v-do’,‘ts’) ). the radius taken from the reference lat long point.

1 Like

Dear @ABraun @thho @Gijs @gnwiii
After completion of stamps, we are generating the mean velocity plot and this result is exported to StaMPS-Visualizer, for better identification of PS points.

1. Before going to generate the CSV file we are providing a reference lat long, why it is required (because we gave a reference, master image right)?
2. Whatever StaMPS-Visualizer plot (displacement vs time) generating with respect to the master image right (In this case why reference lat long is required)?

Thank you.

It is not mandatory but could help to remove false trends from the data. If you enter the location of a stable area here its height difference will be assumed 0 and all other displacements will be shifted accordinly.

If you select no reference in StaMPS, the average displacement of the data is taken as 0-reference.

1 Like

We are keeping the reference image (master image or point) LOS velocity is zero, from zero we are calculating the slave image LOS velocity right?
In this case whatever LOS velocity we are calculating is absolute velocity right?

1. What you keep zero of the reference image, usually is the master, is displacement rather then LOS velocity (you don’t have time period in 1 image).

2. Then you can calculate the displacement of slave relate to the master, now you get how many displacement in time, you can start calculate velocity.

3. Everything you get in PSInSAR result would be a relatively result, which means here is a reference to compare with, in temporal domain, it could be master image or others, in spatial domain, the reference should be a point or an area, which should always be 0 deformation. As default setting, the reference area is setting to the AOI you have processed, which means the average displacement of every interferogram will be 0.

4. As the result, you will always get uplift and subsidence combine in your result. For example, you do know a circular area which is subsiding at the center of your AOI, other area is stable, you will still get a result with subsidence at center and uplift at edge.

5. To select a reference area, you need to use setparm(‘ref_lon’, [lon1 lon2]) and setparm(‘ref_lat’, [lat1 lat2]) to define a boundary of ref area, then use ps_plot(‘v-do’) to update the result, the new result will be relative to the average deformation of all PS inside the area.

The default value of ref_lon / ref_lat is [-inf inf], which means select average of whole PSs as reference.

1 Like

Thank you @constantinevi,
For suppose we have a Permanent GPS station presented in processed AOI, GPS velocities are 2 mm/yr, 5mm/yr, and 6 mm/yr North, East, and Up components respectively. While plotting the ps_plot(‘v-do’, ‘ts’) we are providing the reference lat long point to permanent GPS station coordinates.
Now our reference station up component displacement is 6 mm for 1 year. how can we validate the displacement results of the area?

My question is the vertical displacement of the reference point 6 mm for 1 year, how can we make it to zero?

It would be quite simple while you have a GNSS station, all you have to do is set PS at one GNSS station as 0 mm/year.

Usually we set a little of PSs around GNSS station to prevent some sitution with less and low quility of selected PSs. After that the result become to other area velocity relative to PSs around the GNSS station, than you can simply give the velocity a offset like 6mm/year to make it feat the GNSS velocity. Add a offset to relative value would not change any relationship between PSs, which sholud not cause problems.

The simple way to validate the result is to compare the velocity between others GNSS station and PS around it.

2 Likes

Is there any published paper in this particular topic, please share it?

Thank you.

Maybe you could search with keyword “PSInSAR” and “GPS”, there are lots of result that you can find.

1 Like

In this case, your 3rd point is wrong, right?
The velocity values that we see are relative to the mean velocity of the whole image. We would of course like to have a known velocity point so we could convert them to the absolute velocity values in the LOS direction. We can also set a reference area – with known velocity as our reference. In general, you will want to find an area where no change is expected (if you don’t have GPS measurements).

From RUS tutorial

Well, what I’m talking about in point 3rd is the condition with default reference point setting, also the following 4th point. Although, in this case, the reference have been resetting to a significant point with no deformation, what you get is still a “relative” result, all LOS velocity / displacement is relative to mean value of that point. However, it is still a good way to calibrate the relative result to a frame of velocity / deformation you have already get.

2 Likes

Hello all. (@thho @ABraun @mdelgado )
Currently I am doing a PSI Processing trying to export some displacement results of whole Cyprus island. Through the CyCLOPS program we have installed a network of Corner Reflectors (@6 asc and 6 desc) co-located with a GNSS reference station each. We know the excact coordinates and velocities of each GNSS Station and CR of course. I want to apply this knowledge in my PSI Processing by setting all information in the STAMPS processing. How can I do this? In other words to set more than one reference points or areas in STAMPS and exporting the results?

Kyriaki.

Hi

I am a bit confused about how to set my reference point when it is a GNSS station.

I already did the process in StaMPS and I want to calculate the velocities. I know the velocity of one GNSS station in north, east, up which is located in my AOI.

In the StaMPS parameters there is the ref_velocity option, which by default is 0.

The question is whether I should modify the ref_velocity parameter and indicate the velocity of my GNSS station in LOS or should I leave the default value (in this case, 0)

Thanks for the help

hello mr @fvalverdeuna do you already found the answer to this problem? cause im having the same problem. is it possible to modify the ref_velocity into the known GPS velocity?

I’m still trying to understand how it works or what the ref_velocity parameter does. I did several calculations configuring this parameter and indicating the speed that I know from the reference station and in general it does not modify the results