Adaptive Ground Clutter Removal for Triple-PRT Setup

Our WnD multi-PRT ground clutter removal works in the time domain and the basic filter is similar to the one used in the GMAT algorithm. The filter construction has a unique approach based on statistical analysis, and the output parameter estimation is strongly coupled with the filtering process. We have added a novel system to switch the clutter removal on and off adaptively utilizing dual-polarization data, which we will explain in detail.

Non-uniform pulsing presents an elegant solution to the so-called Doppler dilemma which restricts the measurement of high-speed targets with a pulsed Doppler radar at large distances. We employ a triple-PRT setup capable of handling velocities up to 50 meters per second within a distance of 260 kilometers. Our choice is to send repeated patterns consisting of three pulses separated by intervals of 1750, 2000, and 2500 microseconds (7:8:10 ratio).

We have analyzed and compared different interval ratios, and devised a conceivable means of choosing the best one for fixed range and speed limit boundary conditions. The technique is based on maximizing the accuracy of velocity estimation through an auto-correlation analysis using Gaussian model functions. Moreover, in the case of a cluttered signal, the accuracy of the reflectivity estimation can be improved significantly after obtaining a reliable speed measurement which carries information on the power loss caused by clutter filtering.

Weather radar measurements were made using three different pulsing schemes with the C-band dual-polarization pulsed Doppler radar located in the University of Helsinki Kumpula Campus. The schemes include standard single-PRT measurements, a dual-PRF setup, and a triple-PRT system consisting of repeated patterns of three unequal pulse intervals. The single-PRT and dual-PRF analysis are performed using the original Vaisala software, while the triple-PRT analysis was done on a second computer using our WnD software.

The real-weather measurements demonstrate the that triple-PRT setup is capable of producing accurate estimates even in the presence of ground clutter. We have compared the results directly to GMAP as well as a simple notch filter, including cases of strong winds, snowfall, rainfall, low-altitude melting layers, temperature inversion, anomalous propagation, and biological scatterers.

In addition to measurement data, the software has been tested extensively using simulated radar signals, yielding statistics for, e.g., the reflectivity, speed, and width estimation biases, standard deviations, and error rates.