Estimating Wind Speed and Direction From a Doppler Wind Image

A Doppler wind image from the Buckland Park Doppler radar in Adelaide is shown below.

Doppler velocity image from Buckland Park

Figure 1. Doppler wind image from Buckland Park radar.

Note that the data is patchy - for example, in the northeast corner of the image (around Florieton, Burra and Farrell Flat) there is no Doppler wind data - the shades of brown shown there are the normal topographic shades of the background map. Similarly in the northwest of the image (west of Port Broughton), the grey shades are just the sea surface from the background map. This image actually has a good coverage of Doppler data. On fine weather days, the Doppler data will be much sparser and limited to areas close to the radar. Click here for a larger image

One easily recognisable feature on the image is the zero isodop. It has been highlighted with a pink line in the following image. Click here for a larger image

Doppler velocity image with the zero isodop
highlighted

Figure 2. Doppler wind image with the zero isodop highlighted.

Having identified the zero isodop, we can readily apply the Zero Isodop Method to estimate the wind direction at any point along it. In the image below, we've chosen to look at the point about 25 km NNE of the radar. (Note that the "range rings" shown on the image are at range 50 and 100 km from the radar, which is located at the centre of the image.) Click here for a larger image

Doppler velocity image illustrating zero isodop
method of estimating wind direction

Figure 3. Doppler wind image illustrating the zero isodop method of estimating wind direction.

The Zero Isodop Method estimates that wind at this point is from the ESE. Looking at the table and graph that show how the height of the radar beam changes with distance from the radar shows that this information refers to a point some 430 metres above radar level.

In the following image we estimate the wind over a point about 80 km NNW of the radar. Click here for a larger image

Doppler velocity image illustrating zero isodop
method of estimating wind direction

Figure 4. Estimating the wind direction over a point using the zero isodop method.

Here the wind is blowing from the ENE. The point we are looking at is some 1650 metres above radar level.

The Max/Min Method can also be used to estimate the wind direction. In the image below we've applied it at a range of 60 km and found that the wind to be between E and ESE. Click here for a larger image

Doppler velocity image illustrating max-min method of
estimating wind direction

Figure 5. Doppler wind image illustrating the max/min method of estimating wind direction.

Comparing the shades of the maximum inbound and outbound regions (contained in the small white boxes) to the palette at the bottom of the image shows that the winds speed is approximately 70 km/h. Looking back to the table or graph in the previous section shows that at a range of 60 km, the radar beam is about 1150 metres above radar level.