Making interfrogram by IW sentinel1


#1

Hi everyone. I want to find fast ice displacement and I must use InSAR technique for that.

  1. As I saw in ESA advanced trainting course on remote sensing of cryosphere (second day) in this year to show how to derive Ice Velocity by processing a pair (12 days a part) of Sentinel-1 TOPS Extra Wide Swath (EW_GRDM_1SDH) images by using offset tracking technique.
    I do not think so it can be useful for fast ice displacement because we do not use interferometry in this exercise. Am I right?
  2. I saw three tutorials about interferometry http://step.esa.int/main/doc/tutorials/sentinel-1-toolbox-tutorials/ :
    Sentinel-1 Stripmap Interferometry
    Sentinel-1 TOPSAR Interferometry
    Radarsat-2 Interferometry
    I think I must use Ā“Sentinel-1 TOPSAR InterferometryĀ“ toturial and I must work with IW-SLC products. Am I right?
  3. As I understood, level 1 has 2 sides: GRD and SLC.
    I think we can not use GRD for interferometry because Phase information is lost in GRD.
    Cheers,
    Marjan

#2

Hi Marjan,

I donā€™t think interferometry will be suitable for fast ice displacement due to the lack of coherence between the image pair (cause by the large physical displacement). This paper might be of interest: https://core.ac.uk/download/pdf/58631.pdf.

Note that now that Sentinel1-B is in operation, the time period between imagery can now be 6 days (i.e. a S1-A and S1-B pair) rather than 12 day when only S1-A was in operation.

You are correct in thinking that GRD products are not suitable for interferometry as no phase information is available in this product type.

Peter


#3

It might work for ā€œfast iceā€ that is by definition attached to the shore, if the conditions are favourable.


#4

As I know interferometry, Interferometric synthetic aperture radar (InSAR) exploits the phase difference between two complex radar SAR observations taken from slightly different sensor positions and extracts information about the earthā€™s surface and if EW and IW are interferometry and we have phase in interferometry, then why we are using EW-GRD or IW-GRD products though they do not have information about phase?
How EW-GRD or IW-GRD are useful for ice velocity? I think if we know about ice velocity, then we can know about ice displacement without using EW-SLC or IW-SLC?
Cheers,
Marjan


#5

we used EW-GRD mode for calculating ice velocity. I think if we know about ice velocity, then we can know about ice displacement with very common formula maybe:

displacement= velocity*time

then, Why we are using EW-SLC or IW-SLC for calculating displacement?

I think we can get displacement with calculating ice velocity (EW-GRD) without using EW-SLC or IW-SLC products?

Cheers,

Marjan


#6

I think you may be confusing two different methods for two different purposes. InSAR can measure small movements of the ground using the phase differences of two or more SLC products.

Offset tracking can measure fast moving large areas of ā€˜groundā€™ by matching the same features in a pair of images. Detected GRDs can be used for this purpose.
Speckle tracking can use speckle as a feature to match where things have moved. SLCs can be used for this.


#7

I found that Offset tracking is now implemented in SNAP, which will use the GRD data. Can we perform Speckle tracking in SNAP for the current version?


#8

Take a look on the following pdf to be informed about the steps and the theory behind of Glacier velocity in SNAP.

to have more information: this method in SNAP is just useful to detect large displacement and it uses just intensity not phase information. this method doesnā€™t work to detect small displacement happened by landslideā€¦ look at the following link:

SNAP works well to detect Glacier Velocity but on sea-ice it doesnā€™t work.
as I forced to code to extract the displacement on sea-ice.
the method that most of the researchers use to extract sea-ice velocity is based on feature tracking and matching cross correlationā€¦