Hello.

I have a point shapefile representing the location of weather stations; for each point, the wind speed and wind direction (in degrees) is recorded. I need to create a cotninous surface (i.e., a raster) representing the wind direction in a given area.

In order to do that, I would like to follow the procedure described by:

Safadi, C., 2016. Wind and wave modelling for the evaluation of the maritime accessibility and protection afforded by ancient harbours, Journal of Archaeological Science: Reports 5, 348–60.

which in turn relies on:

Williams, R., 1999. Non-linear surface interpolations: which way is the wind blowing? Paper presented at the ESRI Conference Proceedings, 1999 (which can be found at the link provided below).

The procedure, which I do not totally grasp (as I will elaborate on in what follows), is graphically synthesized by Safadi in the attached image.

I understand that:

(1) the wind direction is first split into two components, using the sine and cosine of the wind direction, so obtaining two values indicated with X' and Y' in the attached image;

(2) the two components are interpolated, so obtaining two (separated) rasters;

(3) the two resulting rasters are used to calculate the alpha angle that, following the indications in the attached image, should be equal to TAN-1Y'/X'.

Now, what I do not follow is:

-in step (1) above, shall I take the sine and cosine of the wind direction only, or these must be multiplied by H (see the upper-left part of the attached image)?

-the last step of the procedure, the one that is indicated at point c of the attached image, is rather obscure to me.

Would anyone mind to clarify the above points, with possible reference to actual GIS (preferably, ArcGIS) procedures? Thank you for any guidance you will kindly provide.

http://mmc2.geofisica.unam.mx/cursos/geoest/Articulos/Geostatistics/Non-Linear%20Surface%20Interpolations.htm

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