Change detection and ratio

[ABraun]

@gabbro: It could certainly improve the result, good point.

[gabrielaquintana77]

Hi people

I did the coregistration, but I used NEST this time… I don’t understand why SNAP cannot makes an good coresgitration for ALOS PALSAR images

Best regards

[gabrielaquintana77]

Now, the change detection with the stack in NEST

[gabrielaquintana77]

Change Detection in Colour by SNAP, ALOS PALSAR images (08/07/2007 and 23/08/2007)

[ABraun]

this is interesting.
How could the differences in registration accuracy arise?

[FTP]

Hi
I have some question about change detection
first of all what is the best data format for change detection? slc or grd / IW or EW or WV or SM/ and what polarization?

second is there any tutorial or step by step processing guide for doing change detection?

[gabrielaquintana77]

Hi people

Someone know how open ALOS PALSAR data in level 1.0 in SNAP?

Thanks for advance

[ABraun]

Level 1.0 data cannot be opened in SNAP. It is basically Level 0 but with orbit information and some bit adjustments.
You need at least Level 1.1 (corresponds to a SLC image) or level 1.5 (MGD).

[gabrielaquintana77]

Thanks ABraun !!!

[gabrielaquintana77]

Hi all

I have an question

Exist one way for to georeference ALOS PALSAR images (1.5) with SNAP? I cannot make terrain correction with SNAP, which other way I should to implement?

[ABraun]

this answer from lveci explains why it doesn’t work:

Alos 2 Geo-reference

The 1.5G is already map projected so you can’t use terrain correction which assumes the data is in SAR geometry. You should be able to use map reprojection but this won’t correct SAR geometric effects. Can you get 1.5 detected products which are not map projected? ie 1.5 and not 1.5G Otherwise, use the 1.1 data.

Gus Ortiz suggested a solution for areas with lesser topography

ALOS-1 L1.5 Terrain Correction

I did a “trick” that solved it: used the SAR-Mosaic with only 01 image. The output is corrected.

For ALOS 1.5 data I had some good experiences with ASF MapReady:
https://www.asf.alaska.edu/data-tools/mapready/2

It allows calibrating, terrain correcting (both geometrically and radiometrically) and geocoding your image.

[gabrielaquintana77]

Thanks ABraun!!!

[gabrielaquintana77]

Hi again

Now, I have other question

How can to export the bands of: composition multitemporal in RGB, log ratio and segmentation like individual bands in format .tiff in SNAP???

[gabrielaquintana77]

Hi all

Screenshot of my processing for make terrain correction of ALOS PALSAR images with SAR Mosaic in SNAP, I don’t believe that geometric distortion was corrected!!! I have doubt

Left: image with SAR mosaic, Right: Image without SAR mosaic

[mengdahl]

Terrain correct first, then mosaic.

[gabrielaquintana77]

Hi Mengdahl

@gabrielaquintana77

Hi all

I have an question

Exist one way for to georeference ALOS PALSAR images (1.5) with SNAP? I cannot make terrain correction with SNAP, which other way I should to implement?

and ABraun replay for me with this:

@ABraun

this answer from lveci explains why it doesn’t work:

Alos 2 Geo-reference

The 1.5G is already map projected so you can’t use terrain correction which assumes the data is in SAR geometry. You should be able to use map reprojection but this won’t correct SAR geometric effects. Can you get 1.5 detected products which are not map projected? ie 1.5 and not 1.5G Otherwise, use the 1.1 data.

@ABraun

Gus Ortiz suggested a solution for areas with lesser topography

ALOS-1 L1.5 Terrain Correction

I did a “trick” that solved it: - used the SAR-Mosaic with only 01 image. The output is corrected.

[ABraun]

this was a misunderstanding. The work-around with the mosaic doesn’t address terrain-induced distortions. It just helps you projecting Level 1.5 data which is currently not supported by the RD Terrain Correction module or the reproject module.

[gabrielaquintana77]

Thanks ABraun.

I readed that geometric distortion are corrected with terrain correction, but this I cannot makes for ALOS PALSAR in SNAP, so, how could make this ??? Please help

[mengdahl]

As Luis noted above, you need to have your ALOS acquisitions in suitable format:

The 1.5G is already map projected so you can’t use terrain correction which assumes the data is in SAR geometry. You should be able to use map reprojection but this won’t correct SAR geometric effects. Can you get 1.5 detected products which are not map projected? ie 1.5 and not 1.5G Otherwise, use the 1.1 data.

Is reordering the data a possibility?

[ABraun]

ASF MapReady performs really good on Level 1.5 data and is quite easy to use.