I do not know for sure if I can ask this stuff here, since I am not using SNAP for my Analysis.
I am trying to do a TimeSeries in Google Earth Engine for Pixels in a lake in Sweden. But I get very different Values for different Images that were taken right after another, I am pretty sure that this might be because of differences in the incidence angle.
According to the website of GEE, they do the following preprocessing themselfes:
- Apply orbit file
- Updates orbit metadata with a restituted orbit file.
- GRD border noise removal
- Removes low intensity noise and invalid data on scene edges. (As of January 12, 2018)
- Thermal noise removal
- Removes additive noise in sub-swaths to help reduce discontinuities between sub-swaths for scenes in multi-swath acquisition modes. (This operation cannot be applied to images produced before July 2015)
- Radiometric calibration
- Computes backscatter intensity using sensor calibration parameters in the GRD metadata.
- Terrain correction (orthorectification)
Here u can see my result:
Here is a chart of the angle-values: (Ignore the y-axis name, I just did not change the code)
As you can see, for the 27th of Novembre, there are two very different Values for VV/VH, even though there might be some differences, they should not be that big.
Is there a mathematical way to correct for the incidence angle by now? I found this topic Incidence angle correction of Sentinel 1 but it did not really help me.
Edit: I just realised, I did the same Preprocessing (+Speckle Filtering) in SNAP to get a first time series, but did not check the angles. So the problem should also be apperaing in SNAP if I downloaded all available data?
With best regards,