Hi
Do forum members know anyone in the Met Bureau who is knowledgeable about the tech aspects of the rain radar?
I'd really love to hear the a detailed tech explanation as to why the Laverton radar is prone to showing circular artefacts in its colour coding of the expected precipitation.
Up until late 2017, the Laverton radar was showing some consistent white radial artefacts, and I posted a query about them in 2017.
Then in late 2017 the radar was upgraded. I gather the beam polarisation was changed, and the new radar can also detect horizontal rain velocity.
The radial artefacts disappeared: but instead, we often see annular or concentric artefacts in which the colour coding of the expected precipitation varies abruptly at certain distances from the radar. This is much worse on some days than others. As an example, the left image below is from a couple of days ago. This is taken from the normal loop radar website at http://www.bom.gov.au/products/IDR024.loop.shtml#skip, although it looks different because I have turned off the Locations, Range and Topography features. If you do this, you can download just rain intensity overlay, as a PNG file with transparency.
You can see that there is a sudden change in the coding of rain intensity at a fixed radius. On many rainy days you can see multiple bands, all concentric on Laverton, as shown on the next recent image (from last week).
This is a gross artefact. You can see that the colour coding is highly unreliable at a given ground location, and may be anywhere between light blue (~2 mm/hr) and perhaps red (120mm/hr), although the context shows this is impossible, and it is clearly not just due to cloud movement. The old radial artefact affected very little of the image, but this one, at its worst, makes most of the image unreliable. Often it looks like a periodic radial saw-tooth function has been applied to the raw data values. It seems to be worse recently, but I have noticed its presence many times since the "upgrade" in 2017, and I would really like to know why it happens, and why it hasn't been fixed after 2 years.