Date/Time Difference in Sentinel 1


#1

Hello all,

So I am working with Google Earth Engine and I have retrieved all of the viable Sentinel 1 returns over my region of interest. By viable, I mean that I have filtered all sentinel 1 returns spatially over my area, temporally to all available data, filtered to GRD products only, filtered to IW instrument mode only, and the filtered to ascending pass only. Finally, I filtered the returns from that selection and split the returns into sentinel 1a and sentinel 1b. I then take the mean over my region of interest and plot the results. However, I am noticing that the time stamps of the returned data is odd. Here is what I am receiving…
Below is a 10 file sample of my exported file names. They are saved as YYYY-MM-dd T hh:mm:ss My question is this: why are the minute time stamp observations going back and forth between 05 and 21? Should they not all be the same? When plotted, the data is distinctly different. I originally thought it was maybe ascending/descending difference but I filtered for that and the time difference is too small. Then I thought that it was the difference between sentinel 1a and 1b but I filtered for that as well too. Now I’m assuming this is related to the incidence angle or look angle of the acquisition but how do I know what angle corresponds to which set of data? I’m calling the sets the “5” minute return set and the “21” minute return set. Please advise.

2015-04-22T03:21:56
2015-04-24T03:05:29
2015-12-18T03:21:57
2016-01-25T03:05:36
2016-07-09T03:21:50
2016-07-21T03:22:04
2016-08-02T03:21:51
2016-08-14T03:22:04
2016-08-16T03:05:45
2016-08-26T03:21:52
2016-09-07T03:22:06
2016-11-24T03:21:23
2016-11-26T03:05:04


#2

Looks like your site is covered by two ascending orbits tracks and the the corresponding incidence-angles are different.


#3

Hi, I would also suggest that your products are from two tracks - check the relative orbit given in the manifest file (parameter relativeOrbitNumber). Also you may wish to examine the planning over your site - Google Earth kml files are available at:

https://sentinel.esa.int/web/sentinel/missions/sentinel-1/observation-scenario/acquisition-segments

The red tracks are for IW.