Inverted dirrection of the wind field when use CDOP

[korvinos]

Description

The calculations of the wind with CDOP algorithm returns inversed wind field, i.e. if we have positive values of the Doppler shift in SAR signal, we will get a negative value (opposite direction) in the find field and vice versa.

For example:

Solution

The problem is in the wind direction. Wind direction should be defined in relation to the SAR look direction

TODO

• [x] Make a test with CDOP algorithm without the openwind package
• [x] Check wind direction field in the input of the algorithm

[mortenwh]

Also remember to check the directional conventions in sar-doppler - I think the problem is probably there...

On 7 February 2018 at 13:28, Artem Moiseev notifications@github.com wrote:

Description

The calculations of the wind with CDOP algorithm returns inversed wind field, i.e. if we have positive values of the Doppler shift in SAR signal, we will get a negative value (opposite direction) in the find field and vice versa.

For example:

[image: geoph_doppler_shift] https://user-images.githubusercontent.com/16581337/35916421-a5790d88-0c0a-11e8-9557-e215336854d6.png [image: doppler_wind_cdop] https://user-images.githubusercontent.com/16581337/35916453-bc7c6994-0c0a-11e8-91be-46d2ab019f73.png

TODO

• Make a test with CDOP algorithm without the openwind package

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[korvinos]

@mortenwh, ok, got it. But now I made a test with pure CDOP from openwind:

from openwind import cdop
ncep_wind = Nansat(ncep_filename)
ncep_wind.reproject(asar, eResampleAlg=1, tps=True)

cdop_wind = cdop(ncep_wind['windspeed'], ncep_wind['winddirection'], asar['incidence_angle'], 'VV')

And got the same stuff:

[mortenwh]

ok, this could be the reason for the error actually... If it is the same input parameters that are used...

The thing is that the wind direction should be defined in relation to the SAR look direction, not relative to north as in the ncep file. It could be as simple as a forgotten or wrong implementation of look relative wind direction.

[korvinos]

@mortenwh, well, seems like it is not implemented in the sar-doppler package

[mortenwh]

but where is it implemented? only in your scripts?

[korvinos]

@mortenwh, Nowhere yet, I will create a separate issue in the sar-doppler because the problem not in the openwind and I think that the solution implemented in the sar-doppler package. So this issue could be closed

[mortenwh]

ok

On 7 February 2018 at 15:11, Artem Moiseev notifications@github.com wrote:

@mortenwh https://github.com/mortenwh, Nowhere yet, I will create a separate issue in the sar-doppler because the problem not in the openwind and I think that the solution implemented in the sar-doppler package. So this issue could be closed

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