yes, the pattern is in all bands:
Now I selected no input band and get different stripes regarding the number of looks:
Maybe some Azimuth-Range ratios are enhancing the patterns while others don’t.
4-1 Looks
6-2 Looks
10-3 Looks
The pattern there is totally normal for the i/q bands, with or without multilooking. I was meaning the intensity band. In my case I have the pattern in i/q bands, but in the intensity computation, the ramp vanishes
Or ar you meaning that you are using i and q bands to make RGB composition?
Yes, sure. But it is strange that after multi-looking it is introduced again.
My RGBs are made with intensities.
We need to check/update the implementation of multilooking, it’s from the early days of NEST and notice that it has has a disclaimer saying that for complex products it is done “without resampling”.
yes, I guessed that this is one of the reasons for the pattens above.
It says that about detection - we will check. Could someone post a graph + data products that replicate the problem?
thank you.
My data was
S1B_IW_SLC__1SDV_20170918T053347_20170918T053415_007442_00D231_7B85
I applied:
- TOPS Split (IW2, burst 5 only)
- TOPS Deburst
- Multi-look with 4/1, 6/2 and 10/3 looks
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I am seeing similar artefacts when multi-looking 4/1 is applied in various complex products sources at SNAP, including other platforms (TerraSAR). This seems to be an issue impacting more than one user.
For Crop classification what are the processing steps of Sentinel1 SLC data?
I am using multi temporal Sentinel1 SLC IW data for classifying crop types. And to process them in SNAP, i am using the following steps:
- Tops-Split/Deburst/Merge
- Apply Orbit file
- Callibrate (output sigma band for VV and VH)
- Speckle filter (filter Gamma map (3/3))
- Multilook
- Terrain Correction
Can anybody confirm the steps to be correct and appropriate for crop classification. Thanks in advance.
For classification purposese, Sentinel-1 GRD data is sufficient. I see no point in downloading, debursting and merging SLC data, to be honest. If wou worked on GRD data you could simply skip the first step and directly apply the orbit file and calibrate to Sigma.
Multi-looking is also not advisable for GRD data because the data are already in ground range.
Did you see this: Radiometric & Geometric Correction Workflow
And you can working with subsets if you use GRD data…
sure, you can subset it at any time.
Since the burst image is modulated in azimuth, the azimuth spectrum has a phase ramp. Generally if we want to perform operations between pixels, such as interpolation, we should apply deramping first to the signal and apply reramping later after the operation in order to preserve the phase information. Therefore, we should not apply multilook to the complex image unless the image is deramped.
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@jun_lu That’s totally true. However, for some reasons, I would like to deramp my images too. Does SNAP has any way to deramp my images?
In the back geocoding process, you can output the demod/deramped phase. But how to use it?
I tried the following :
- From the I/Q of the slave image, i recompute the amplitude and phase
- I remod the phase ramp and remove it from the slave phase image
- I recompute I/Q in order to have a deramped slave image
I still have this phase this phase ramp in azimuth. Did I do something wrong?
Currently SNAP does not have an operator to deramp the image. I think in theory you can deramp the coregistered slave image using the demod/deramp phase output from backgeocoding. But I have never tried.
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I tried (Several times actually) but never managed to deramp it. I will try again. If it works (or not), I will tag you with the procedures / results. It may interests other people too
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Hi thanks for the steps given above . But for my data of SLC IW, the above steps worked out only upto Polarimetric Unsupervised classification… for the next step of decomposition it gives the exeception as “Input should be polarimetric”… Kindly clarify me …Thanks in advance
Sentinel-1 has only two polarizations VV/VH, but for most decompositions you need quad-pol data.
Please see here: Sentinel-1 SLC Polarimetric Decomposition and here H-Alpha Plane Problems
Hi,
Usually all these dual decomposition and classification are meant for polarimetric data with HH and HV or compact polarised data with RH and RV, but sentinel 1 data are available with VV and VH polarization. There must be some diffrence between the two.
Thanks