Is Multilooking a tool only to reduce the speckle in SLC SAR images?
December 11, 2021, 4:13pm
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I am fairly new to the SAR processing and I am trying to learn the basics through the ESA Sentinel Toolbox tutorials, which are a valuable resource.
In the very first tutorial “SAR Basic Tutorial”, I don’t understand the role of the Multilooking process specially when compared with Geocoding.
According to the tutorial, the “Multilooking can be an optional step, since it is not necessary when terrain correcting an image”. But in the Terrain correction step of the tutorial, the input ima…
yes, GRD is already multi-looked. It is not a mandatory step, because before you can use SAR data in a GIS you have to geocode them which is done in SNAP during the Range Doppler Terrain Correction which also applies a resampling, resulting in square pixels anyway.
Multi-looking is good to make SLC data easier to handle but it makes little sense for GRD data unless you want to systematically alter the spatial resolution at consistent intervals.
it means that its already ground-range corrected. Unlike SLC data the pixels’ areas are already of same size.
Astrium has made nice graphics for this case. They refer to TerraSAR-X but the principle is the same for most SAR satellites:
Slant Range Complex (SLC/SSC/L.1.1)
Data is neither multi-looked nor projected
Ground Range Detected (GRD/MGD/L1.5)
Data is multi-looked but not projected
Geocoded Ellipsoid Corrected (GEC/L2.0)
Data is projected but topographic d…
So, Multilooking tool makes that pixels of the image become from rectangular to squares, but that helps to reduce the speckle in the interferograms?, because someone told me that the speckle only affects GRD images and no SLC images when I apply Interferometry. So, I am confused.
December 11, 2021, 6:29pm
It can also be applied to interferograms.
But the filtering effect has its limits when the image or interferogram quality is bad.
What data do you use?
I am using SLC (Single Look Complex) data.
December 12, 2021, 7:04pm
Sorry, I meant which sensor.
Can you please provide a screenshot of the interferogram?
CSAR sensor from Sentinel-1