GAMMA Questions

Dear everyone，
Hello， I also meet same questions of direction fields using POT. How can I transform velocity field of range-azimuth into north-south and east-west velocity in GAMMA.
Best
Alain Ween

Hello,

First you should terrain geocode the scene and generate a look up table.
Then terrain geocode your offset deformation map into map coordinates.

The program lk_vec_lt can be used to calculate the look vector for each point in
the geocoded image. The look vector is in terms of East north up. (ENU basis).

Then use the program to dispmap_ENU to take multiple observations and solve for
the 3D deformation field.
You have to have 3 observations or other observations to fully constrain the
deformation field.
SVD is used to solve the 3D deformation field. If the system of equations is
under determined, then the deformation in the unknown direction is forced to
0.0. You only have deformation (velocity) information along the look vector for
interferometric measurements, There is no sensitivity to deformation in the
plane orthogonal to the look vector. if the radar is looking orthogonal to the
velocity vector, there will be no sensitivity to motion in the plane containing
the orbit.  The Look vector is usually mostly in the East-West direction at
lower latitudes.

Best regards,
Charles Werner

yeah， thanks for your reply.
Here, I didn't need get 3D velocity and get 2D (E-N) without U based on offset tracking results from range-azimuth direction. We get an heading angle in slc.par file.

ew=range*cos(head)+azi*sin(head);
ns=-range*sin(head)+azi*cos(head);

just an rotation of coordinates.

It's OKay?

best
Alain Ween

Hello,

That should be ok if you assume no vertical motion, and constrain deformation to
be only to the X-Y plane. I would however scale the range deformation to be
horizontal to the ground, since the slant range is tilted by the incidence
angle, delta_ground_range = delta_range/sin(inc).

Best regards,
Charles

Hi,
be careful, when using the heading angle from the SLC-par file for converting range/azimuth displacement fields to EW/NS coordinates. It can cause significant offsets in the displacement direction.

Thorsten

Hi，
which factor could cause the significant offsets in the direction? Is there have other method just for 2D field.

Best
Alain

At least for Sentinel-1 data, the azimuth direction of the tracking results do not fit to the heading angle in the slc.par file for higher lat.
I tried to generate the offset of the azimuth direction from the "SLC_corners" information. The results were better but there was still an offset.

Hi,

My study area just in Antarctic using S1 data. Can you describle your details of process except using command "SLC_corners".
How to transform field.

Hi,

take the coordinates returned from

SLC_corners and parse it to a text file.

and compute the heading based on the coordinates.

I use R to do the processing

t<-read.table("slc-corners.txt",skip=2,nrows=4 ) # read corner coords
t3<-t[3,]
t[3,]<-t[4,]
t[4,]<-t3
t<-cbind(t[,6],t[,3])
heading<-(bearing(t[2,],t[3,])+bearing(t[1,],t[4,]))/2 # calc. heading based on MLI corners
cat ("heading:", heading, "\n")

I use the average value from the "western" and "eastern" corners, since both differ slightly.

The flowlines are still not perfect and need some corrections but still better than using the heading from the slc.par

Thorsten

Really, thanks.