Median maps for radar pairs

The radar pair pictures give the median value of the difference in reflectivities seen by the radars. The difference is shown on a colour palette, where white shows points with reflectivities within 1 dB. Each colours has a width of 3 dBZ. Occasionally the difference may exceed 15 dBZ (in absolute value). These are shown by the last colour in the palette.

The pictures gives us a way to decide whether the radars have a difference in calibration. We can also find out what is the difference in the lowest elevation angles. I proper determination of these is only possible by numerical means, but a look by naked eye is able to reveal qualitative information on the calibration and angle differences.

The Anjalankoski-Ikaalinen pair (left) from October is a simple case. As ANJ is the first radar in the pair, the positive values of the difference denote that Anjalankoski radar sees a stonger signal at that point. These are towards the south-east, i.e. towards the Anjalankoski radar. The zero difference line goes parallel to the bisector of the plot indicating that the lowest elevation of the radars are the same. However, the bisector lies where the white and green colours meet, indicating that the difference is slightly positive, 1 ... 2 dBZ. Hence we may conclude that the ANJ radar measured slightly higher reflectivities.

You will find pictures with highly variable features in the radar pair directories. Once the analysis software is running, we can attach an estimate of the angle difference and of the calibration difference to each of the pictures.

A report by Robin King explains how one can analyze the pictures visually as well as numerically.