1,721,161 research outputs found
Initial Examination of AltiKa's Individual Echoes
No full textThe AltiKa altimeter records the reflection of Ka-band radar pulses from the Earth's surface, with the commonly used waveform product involving the summation of 96 returns to provide average echoes at 40 Hz. Occasionally there are one-second recordings of the complex individual echoes (IEs), which facilitate the evaluation of on-board processing and offer the potential for new processing strategies. Our investigation of these IEs over the ocean confirms the on-board operations, whilst noting that data quantization limits the accuracy in the thermal noise region. By constructing average waveforms from 32 IEs at a time, and applying an innovative subwaveform retracker, we demonstrate that accurate height and wave height information can be retrieved from very short sections of data. Early exploration of the complex echoes reveals structure in the phase information similar to that noted for Envisat's IEs
Steric sea level variations in the central-eastern Mediterranean Sea from Argo observations
No full textTemporal variations of the sea level have been assessed by means of satellite altimetry for many years. While the total sea level change is determined by altimetry very precisely, at the level of a few millimeters, knowledge of the effects of mass-related and volume-related contributions is comparatively poor. Here, we report on the effect of volume changes of sea water in the central-eastern Mediterranean Sea. The study is performed on the basis of in-situ data collected by the floats of the Mediterranean and Black Sea Argo Centre (MedArgo) established in 2003. On a grid of 1°×1° the total steric sea level variations as well as the individual contributions of thermal and haline expansion are computed. The study reveals a strong volume-related, sea level change at a rate of about 18 mm/year between 2004 and the end of 2008 in the Ionian Sea that is clearly dominated by thermal expansion. In contrast, thermal and haline contributions show opposite trends in the eastern Mediterranean Sea where both effects tend to counteract each other on inter-annual time scales. Steric sea level changes from Argo and the total sea level change from the altimetry satellite mission Jason-1 agree very well in the Ionian Sea, suggesting that most of the observed sea level rise is caused by thermal expansion in this region. However, the comparison of Jason-1 with the steric sea level change computed from Argo data between 2004 and the end of 2007 indicates an unexplained mass loss at a rate of -20 mm/year in the region around Crete
LPV model identification of a flapping wing MAV
Full text linkThe problem of model identification for the local dynamics of a flapping wing MAY is considered. Following a discussion of the underlying modelling challenges, an approach to model identification is proposed and two subspace model identification methods for LTP and LPV systems are applied and compared, with the aim of obtaining a high fidelity model of the MAY dynamics
Influence of river meandering on the Tagliamento floods
No full textIn this paper is presented a bi-dimensional approach to the study of flood of the Tagliamento River in the
presence of meanders. It deals with a 2D depth-averaged numerical model based on conservative form of De
Saint Venant equations. A finite volume method is used to solve non linear equations by a Godunov approach
supported by a robust and efficient approximate solver proposed by Harten, Lax and van Leer (HLL). First,
we show the ability of the model to understand the variations in the level of cross-curve due to centrifugal acceleration.
To this end, it is shown a comparison between the experimental results of Shukry (1950) and similar
numerical simulations. Following is discussed behaviour levels in the meanders of low Tagliamento during the
flood event of 4 November 1966
Modellazione ai volumi finiti dell’onda generata dalla frana del Vajont il 9 ottobre 1963
No full textLa frana del Vajont del 9 ottobre 1963 causò un’onda, che spazzò l’intero bacino artificiale e tracimò colpendo pesantemente anche la valle del Piave. La frana è stata oggetto di numerosissimi studi a carattere prevalentemente geologico e geotecnico, mentre sono state condotte poche analisi idrauliche del fenomeno. Nella presente memoria a seguito degli sviluppi che la modellistica numerica ha avuto negli ultimi decenni si propone un modello numerico 2DH ai volumi finiti per lo studio idrodinamico dell’onda generata dalla frana
- …
