Določanje radialne komponente vetra iz meritev Dopplerjevega radarja

Švagelj, Vito (author), Skok, Gregor (mentor), Strajnar, Benedikt (comentor), Zgonc, Anton (comentor)

Dopplerjev vremenski radar meri radialno hitrost hidrometeorjev v ozračju z merjenjem spremembe faze med dvema zaporednima odbitima sunkoma elektromagnetnega valovanja. Interval, na katerem lahko radar enolično določi hitrost, je omejen z Nyquistovo hitrostjo. Prave radialne hitrosti, ki so izven merjenega intervala, se preslikajo na ta omejen interval, zato lahko vetrovno polje vsebuje nezveznosti. V Sloveniji sta dva meteorološka radarja, ki imata majhen interval hitrosti, zato so potrebne metode, ki skušajo enolično določiti izmerjene hitrosti. Popravljeno vetrovno polje je potencialno uporabno pri izračunu vremenske napovedi. V tem magistrskemu delu so predstavljene tri takšne metode in verifikacija le-teh s pomočjo radiosondažne meritve in napovedi modela ALADIN. Analizo meritev sem izvajal na obeh meteoroloških radarjih v Sloveniji. Za analizo sem z vizualno oceno na vsakem radarju izbral približno 750 pet ali deset minutnih meritev, skupaj 1500 meritev. Izbiral sem primere, pri katerih sem ocenil, da so prisotne padavine na večjem območju Slovenije in so relativno nizke intenzitete. Analiza subjektivno določene uspešnosti metod je pokazala, da je najboljša metoda s torusno preslikavo, ki je uspešno popravila približno 50 % meritev. S približno 25 % uspešnostjo je druga najboljša Meierjeva metoda. Še približno polovico manj uspešna je metoda CINDA. Primerjava z radiosondažo je pokazala majhne razlike med vsemi tremi metodami. Enako je pokazala tudi primerjava z modelom. V vseh primerjavah so metode izboljšale napake v primerjavi z nepopravljenimi radarskimi meritvami hitrosti.

• Language: Slovenian
• Keywords: vremenski radar, Dopplerjev radar, Nyquistova hitrost, dealiasing, vertikalna radiosondaža
• Work type: Master's thesis/paper
• Typology: 2.09 - Master's Thesis
• Organization: FMF - Faculty of Mathematics and Physics
• Year: 2020
• PID: 20.500.12556/RUL-121908
• COBISS.SI-ID: 36981251
• Publication date in RUL: 07.11.2020

Secondary language

• Language: English
• Title: Dealiasing radial wind from Doppler weather radar measurements

Abstract

Doppler weather radar determines radial velocity from observed phase difference between successive pulses of electromagnetic radiation. There is an interval in which velocities can be determined unambiguously. Size of the interval is defned with Nyquist velocity. Velocities greater than Nyquist velocity are aliased inside the interval. Therefore there can be some discontinuities in the fields of radial velocity. In Slovenia there are two weather radars that have a low Nyquist velocity therefore methods for dealiasing are needed. Dealiased wind fields can be potentially used in weather prediction models. In this Master's thesis three methods for dealiasing and their verification are presented. Limited area numerical weather prediction model ALADIN and radiosonde are used for verification. The analysis was carried out on two weather Doppler radars that are located in Slovenia. Using a subjective visual analysis I chose approximately 750 five or ten minute measurements on each radar, together 1500 measurements. I chose cases where precipitation covers the majority of the area over Slovenia and intensity is relatively low. Subjective analysis of dealiasing showed the best method is Torus Mapping. It was successful in about 50 % of cases. Next was Meier method with about 25 % success rate. The least successful was CINDA method with about 13 % successful cases. Comparison with radiosonde and ALADIN was inconclusive because the differences between the methods were too small. In all cases all methods improved the results of original unmodified measurements.

• Keywords: weather radar, Doppler radar, Nyquist velocity, dealiasing, vertical radiosonde