Wind Field Estimation process bug?

As a part of my project proceeding, I have encounter with an issue which I tried to solve but I couldn’t. Hereby I would like to inform you that in Wind Field Estimation using SNAP software tool, the wind direction is indicating in two headed arrow mark. I could not understand how can I find the exact wind direction with one headed arrow mark. It is my pleasure if I get the procedure to rectify this problem. Kindly help me to get rid of this. Thank you

Here is the product which I am using for my case study- Refugio Oil Spill, north of Refugio State Beach in Santa Barbara County, California.
Product: S1A_IW_GRDH_1SSV_20150531T015813_20150531T015838_006159_008023_EF9E

You need external data, for example a weather-report, to remove the 180-degree ambiguity. Is this not explained in the help, I think the info should be there?

Dear Mengdahl,

Thank you for your kind reply. Yes, I went through the SNAP help menu but didn’t find any method or process to remove the 180-degree ambiguity. Can you please clarify, what kind of external data require to remove the 180-degree ambiguity?

Thanks and regards,

Mohammed Irshad P

External data like a weather forecast with information on general wind direction.

Dear Mengdahl.

Thanks once again for your kind help. If you help me for the final time I would be thankful. Please just help me from where can I get the weather forecast information (on general wind direction) for below sentinel 1 data for the same date and place.

Product: S1A_IW_GRDH_1SSV_20150531T015813_20150531T015838_006159_008023_EF9E

Place: North of Refugio State Beach in Santa Barbara County, California.

Date: 31-05-2015 (1:58:13)

Thanks and regards,

Mohammed Irshad P

This site has historic buoy data for off the coast of the US, quite a few situated off Refrugio.

I was also looking at the oil slick there using S1a - did you get a good result with the oil slick detection? I was not happy with mine. I would love to hear what steps/parameters you used if it is something you don;t mind sharing.

Even I was not happy with mine too. I tried with different parameters to get good results but the results were not satisfied. Better try to use these parameters may be you get better result as I tried for different case study, somewhat got good result.

Following criteria has been fulfilled for the detection of the Oil Spill:
 Source Product: Oil Spill detection
 Source Bands: Sigma0_vv (With checked out Mask out the land* box).
 Background window size : 20
 Threshold Shift: 2.0(dB)
 Minimum Cluster Size:

I asked on the forum a few weeks back - a larger window size (512+) seems to help. I tried again with an ENVISAT image of the deepwater spill and it worked ok. i still wasnt happy with results froma smaller spill like refrugio so i was wondering what i am missing…

my old post

Have anyone got single headed arrow in wind field estimation process. Please kindly help me, I am not getting any solution for to make double headed arrow as single headed arrow. As I downloaded external weather report data but i can’t use that in SNAP to make it as single headed arrow.

Please help me I am stuck in that process.

thanks and regards

Mohammed Irshad P

There might be a neater way to do it but what i was going to try was:

  • if I could find the wind results xml file that they refer to in the manual (i cannot find the file on windows- have searched everywhere)
  • use a link similar to the one I gave above for Refrugio to find the correct wind direction (remove the 180 ambiguity).
  • then either delete the incorrect dx:X or dy:Y wind value or if it requires one, make it the same value.
  • replot the results

From the manual:

Wind Field Retrieval Result Report

The wind field estimation results are saved into an xml file .s1tbx/log/wind_field_report.xml with the following information given for each window in which wind estimation is made:

lat: Latitude of the central point in the window.
lon: Longitude of the central point in the window.
speed: Estimated wind speed in m/s.
dx: X component of the estimated wind vector.
dy: Y component of the estimated wind vector.

Thank you for your kind reply con20or,

Can you please explain me how to remove 180 ambiguity by using external wind data?

As you said I downloaded a wind data file which is in .txt file but i can not execute this format. Please help me to solve this issue.

The detail of the wind data for my case study is given below, Please help me how can I remove 180 ambiguity by using these following data

#yr mo dy hr mn degT m/s m/s m sec sec degT hPa degC degC degC mi ft
2015 05 31 01 42 999 99.0 99.0 0.61 11.11 5.81 260 9999.0 999.0 15.4 999.0 99.0 99.00

Thanks and Regards
Mohammed Irshad P

We don’t intend to update the wind field operator further to include online weather models.

Please have a look at the Sentienl-1 Level-2 OCN products on SciHub which include wind.

Dear irshadnagur,
When studying wind field estimation in here, I accidentally saw your problem. You mentioned that you also studied oil spill detection. Could you please share me more information about the oil spill accident information of this product(Product: S1A_IW_GRDH_1SSV_20150531T015813_20150531T015838_006159_008023_EF9E)?

Thanks and regards,
naomi li