Noise é ltering in a variational wind é eld retrieval from Doppler radar

Two different concepts for noise e ltering in a D OPPLER radar wind e eld retrieval are compared. The e rst technique is a smoothing on the raw radar data. The second method uses a smoothness constraint within a variational technique in which a model wind e eld is adjusted to radar data by minimizing a cost function. The wind e eld retrieval algorithm is described by P ROTAT and ZAWADZKI (1999) and is further extended here by adding a topography constraint for its application in mountainous terrain. The experiments are carried out with analytic wind e elds artie cially affected by noise. In a e rst step only the horizontal wind is retrieved. In a second step the continuity equation serves to calculate the three-dimensional wind e eld. Power spectra and an error analysis of the retrieved wind e elds as well as the performance of the algorithm lead to the following results. An efe cient noise e ltering by a mere data smoothing is accompanied by a lack of accuracy in the retrieved wind components. The smoothness constraint eliminates the noise more efe ciently than smoothing of raw data while producing an accurate wind e eld. For the retrieval of the vertical velocity wind e eld, the smoothness constraint is indispensable.