[fatma]

Dear Daniele,

I started to process 2 ALOS data, but after coregistration step i get this error:

Error in cull_points(): fewer than minimum points, only 17 left!
WARNING!!! coregistration of image 20101212 failed!!!!

And then i try to start again (re-run the tool, using SLC data module), “get contents”, check “update”, set orbits, then go to coreg params,check initial shifts from coarse xcorr (my previous procesiing i didn’t change anything from coreg params), then coregister again. Finally i get this warning:

>>
param2orbitstruct: reading from SLC data
Task for UTC time: 08-Mar-2009 20:32:00 and LOCATION: (37.742, 28.835) finished.

Slave images coregistration

get_master_pts: using the previously generated file.

To re-generate it, remove file /home/fatma/Desktop/babadag_sarproz/babadag/EXT/master_pts_infile.txt

Using a coarse cross-correlation to calculate initial co-registration shifts

cross-correlating matrixes

Image pair: 20090308-20101212
The first 5 local maxima have the following reliabilities:
2.1163 0.1047 0.0991 0.0979 0.0953

Estimated shifts: 80, 40

Xcorr correction: -61.0 in range, -5.0 in azimuth

allocating 4300 x 10560 samples, type: 1

allocating 4300 x 10560 samples, type: 3

prep_img: job ended

setimageconf: converting from SLC data

image.conf.mat written for 1 images

set3points: converting from SLC data

orbit files written for 1 images

param2orbitstruct: reading from SLC data
Task for UTC time: 12-Dec-2010 20:32:00 and LOCATION: (37.742, 28.832) finished.

WARNING WARNING WARNING

pair 20090308_20101212: highly probably the shift is too large and the co-registered image has black areas!!!!

The Processing concluded successfully, here a specific message:

Slave images coregistration: job ended

Elapsed Time: 883 seconds
>>
File 20101212_HH.slc not found
>>
1 Slave images have not been extracted!!
>>

And also you can see screenshot from my procesiing steps. How can i solve this problem?

Thank you,

Fatma

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[periz]

The software has some default parameters for coregistration.
If the coregistration fails at the first step, one has to plot the images to check why it failed.
Then, depending on the reason, you can change the coregistration parameters.

In your case, the two images look similar and have corresponding features that can be used for coregistering them.
So, the reason of the failure is that the default parameters (12 “search pixels” in range/azimuth) are not enough to compensate for the shift between Master and Slave. It means that the timing info coming with the orbits is not accurate enough.
This can be solved by modifying the initial shifts: instead of using the orbits, we can use a coarse cross-correlation (tick the corresponding checkbox). (note: you could also increase the “search pixels” values, but this will take longer processing time)

The second message that you got tells you that the estimated shift between the two images is higher than the “buffer” taken for the slave image. It means that you could have black pixels at the border of you output slave.
To solve it, one should increase the value of “delta” in the “data processing” frame, “SLC processing” window. After changing that value, check the box “Ovw” (overwrite) and extract the slave image again. Finally, launch the coregistration.
However, it may not be necessary: probably if you plot the co-registered slave you will not even notice the black border.
If this is the case, you can proceed further with your processing.

Notice that if the coregistration (or any other steps) fails, generally you do not need to repeat processing steps that were already concluded. Make use of the “update”, “overwrite” options and ALWAYS read the messages given by the software.

[uros-djuric]

Hello everyone,

I am trying to follow Yuxiao SAR intereferometry tutorial with two ERS 2 images. I have downloaded 2 time close images (11.2010 and 09.2010). Loading images is fine, I have downloaded orbits manually and selected common area for extraction.

But when I come to co-registration, it always fails and button become yellow. I have read other similar posts in forum, and I have tried all possible combinations (cross-correlation, search window etc) but without success. It is always saying that I do not have enough cull points.

If I visually compare both extracted images, I can see that they are similar but with significant difference. Can someone tells me which parameters for co-registration I should use for such strong difference, and of course is it possible to do it with such data set. Even if I download all other available images from same mission and paths (+- one year), they still have strong difference between them.

Thank you for any advice or suggestion

Uroš

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[periz]

There is not much more to add. Take a bigger reference window, lower the SNR and the correlation thresholds, lower the minimum number of points. are you processing the full frame? if not, do it.
but the question is: what are you using these data for? for sure, no interferometry will be possible.
if you just want to plot the amplitude, you can switch the coregistration mode to “only orbits”. in this way, no shift will be estimated from amplitude cross-correlation, your data will be resampled only based on orbital data
best

[uros-djuric]

Thank you for the suggestion, I will try out them.

are you processing the full frame? if not, do it.

I have tried both options, full frame (max extent) and smaller area.

but the question is: what are you using these data for? for sure, no interferometry will be possible

Actually, I was trying to recreate steps from Yuxiao tutorial (Earthquake), since one image is before (cca two months) and another image is after ten days of the strong and shallow earthquake (M>5.4, depth 10 km, Int. VII-VIII) of epicenter area that is captured on images.

But I already supposed that if I cannot co-register them easily, then I probably could not to any other processing, so now I just wanted to co-register them using different parameters as practice. I suppose that coherence is low due to season change from late summer to mid-autumn and significant changes of vegetational cover between them, but I didn’t have any other pair to download to be so close by capture time and before/after of earthquake event.

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