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I am conducting an exposure assessment and need to isolate downwind populations from numerous points of exposure in the US. I have a shapefile that separates the entire US into 36x36 km cells. Each cell has emissions data and U and V wind values.

The easiest analysis is to create a buffer around each cell to capture the exposed population within x meters, for example. However, that does not take into account wind direction or speed (values that can be derived from the U and V values). Another option would be to calculate a buffer that is weighted towards the prevailing wind, but I do not believe a function in GIS exists to do this.

A step by step alternative would be to first calculate and create wind vectors per cell, and then use the Linear Directional Mean to create a mean vector within designated areas. Then I could buffer around this vector, however this would still be a very crude estimate of the exposed population.

Can anyone suggest a method of creating ellipse-like buffers that preferentially capture downwind areas using ArcGIS Pro (I am not very familiar with ArcPy). If not, I would like to at least be able to create a new layer of vectors based on U and V wind values. (Also, to be clear, I do not want to visualize the wind directions - I know how to do this using symbology. I would like to create a new shapefile of vectors so that I can use the Linear Directional Mean tool.)

  • please give more details about the U and V values. – radouxju Dec 22 '16 at 17:15
  • U wind and V wind are the u and v vector components of wind, where u wind is the cosine component and v wind is the sin component. I have these values (from which speed and direction can be derived) for each 36x36 cell. I would like to create a vector based on these values, so that length would be proportional to speed. – ellejay Dec 30 '16 at 19:01
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in a sense, resistance to wind is the same as resistance to slope for a walker. Therefore you could use some cost path algorithm (e.g. path distance in ArcGIS) to create an anisotropic distance raster. You can then reclassify this raster file in order to generate your "buffers".

  • Sounds very interesting. However, I am not an advanced user. Could you provide a little more detail as to how this could be implemented in arcgis (or a reference)? – ellejay Dec 30 '16 at 19:03
  • just a quick comment, have a look at desktop.arcgis.com/en/arcmap/latest/tools/… for ArcGIS. Note that you shoud use an arcgis tag in order to guide answers in a specific software. I can go into more details later but currently out of time. – radouxju Jan 1 '17 at 12:06
  • Thank you - I have reviewed path analysis and cost path tools. As far as I understand, they can calculate the shortest path between two points using cost information (which in my case would be wind direction and speed). However, I do not have pairs of points - I have many points around which I want to create a buffer based on wind speed and direction. While the underlying theory of incorporating wind-based costs appears very useful, I am not sure to how to implement it to determine a final slope and width/length of ellipse buffer based on wind direction and speed, respectively. – ellejay Jan 2 '17 at 20:13
  • with cost distance, you create a raster. I've edited my answer. – radouxju Jan 3 '17 at 7:50

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