Tuesday, 29 August 2023
Boundary Waters (Hyatt Regency Minneapolis)
Faced with the Doppler dilemma, Météo France opted for a rather original choice.
Wishing to keep PRFs low enough for accurate measurement of precipitation while having the capability to retrieve high radial velocities (beyond 30m/s), Météo France has implemented a triple-PRT scheme (Tabary at al., 2006).
This particular scheme makes it possible to keep a range of 255km and at the same time to be able to retrieve velocities of up to 60m/s.
However, the triple-PRT scheme is particularly sensitive to the measurement noise that affects the quality of the three velocities V1, V2 and V3 inferred from the three PRT and that ultimately induces several dealiasing errors.
The purpose of this presentation is to show how the quality of Doppler velocities can be improved in these conditions.
The first area of improvement concerns the optimization of the PRF used. Indeed, previous simulations conducted at Météo France have shown that the ratio of the three Nyquist velocities has a large impact on the dealiasing performances. From this studies, different optimized triplet have been identified and tested during two experiments on an operational C band radar. The results are in good agreement with the simulation and show an increase in the dealiasing success rate with the optimized triplets.
The second way to improve the scheme is to develop further the dealiasing method. In order to reduce the impact of noise, a 2-dimensional median filter is applied on each of the three velocities V1, V2 and V3 before dealiasing. By proceeding in this way, the quality of the retrieved velocities is already significantly improved.
Then a method to correct the residual dealiasing errors has been developed. Pixel by pixel, the errors are identified by comparing the result of dealiasing method with the median of the neighboring pixels and if the difference is greater than VNyquist a different unfolding number is used.
These three methods combined have significantly improved the quality of Doppler velocities produced by the triple-PRT scheme.
Tabary, P., Guibert, F., Perier, L., & Parent-du-Chatelet, J. (2006). An operational triple-PRT Doppler scheme for the French radar network. Journal of Atmospheric and Oceanic Technology, 23(12), 1645-1656.
Wishing to keep PRFs low enough for accurate measurement of precipitation while having the capability to retrieve high radial velocities (beyond 30m/s), Météo France has implemented a triple-PRT scheme (Tabary at al., 2006).
This particular scheme makes it possible to keep a range of 255km and at the same time to be able to retrieve velocities of up to 60m/s.
However, the triple-PRT scheme is particularly sensitive to the measurement noise that affects the quality of the three velocities V1, V2 and V3 inferred from the three PRT and that ultimately induces several dealiasing errors.
The purpose of this presentation is to show how the quality of Doppler velocities can be improved in these conditions.
The first area of improvement concerns the optimization of the PRF used. Indeed, previous simulations conducted at Météo France have shown that the ratio of the three Nyquist velocities has a large impact on the dealiasing performances. From this studies, different optimized triplet have been identified and tested during two experiments on an operational C band radar. The results are in good agreement with the simulation and show an increase in the dealiasing success rate with the optimized triplets.
The second way to improve the scheme is to develop further the dealiasing method. In order to reduce the impact of noise, a 2-dimensional median filter is applied on each of the three velocities V1, V2 and V3 before dealiasing. By proceeding in this way, the quality of the retrieved velocities is already significantly improved.
Then a method to correct the residual dealiasing errors has been developed. Pixel by pixel, the errors are identified by comparing the result of dealiasing method with the median of the neighboring pixels and if the difference is greater than VNyquist a different unfolding number is used.
These three methods combined have significantly improved the quality of Doppler velocities produced by the triple-PRT scheme.
Tabary, P., Guibert, F., Perier, L., & Parent-du-Chatelet, J. (2006). An operational triple-PRT Doppler scheme for the French radar network. Journal of Atmospheric and Oceanic Technology, 23(12), 1645-1656.
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