3-D Wind measurements with the S-band atmospheric profiler TARA

Starting April 2000, a Transportable Atmospheric RAdar system (TARA) came into operation. This S-band system combines high sensitivity and multi parameter capabilities into one research device. This fully coherent system can measure Doppler spectra and polarization characteristics of a radar target. In fact it can measure the polarimetric characteristics within a Doppler resolution cell. Next to Doppler and polarization capabilities the system has multiple antenna beams that can be used to measure three-dimensional wind fields.

To calculate the three-dimensional wind fields, it has to be assumed that the horizontal correlation length for the wind velocity is sufficiently large. This is in fact the same assumption that has to be made for calculating the wind field from wind profiler data and means that the wind field at the position of the measurement volume of each of the three beams is identical.

In this article, the TARA system as a whole is presented and a short explanation of the method to calculate the three-dimensional wind fields is described. Results as derived from the TARA data are presented. From the results it will be shown that the assumption of long correlation lengths is not always fulfilled. The wind field calculated from the TARA data is compared with results from a boundary layer wind profiler (1290 MHz) and with radio-sounding measurements showing good agreement between the different sensors. It will be shown that TARA data will lead to an improvement of the end product of boundary layer wind profilers, being a wind profile over an extended range of altitudes.