Combined use of SAR and scatterometer for the study of the atmospheric boundary layer

The paper illustrates a possible way of combining SAR images over the sea with scatterometer derived wind fields, to study the spatial characteristics of the marine atmospheric boundary layer (MABL). Both instruments are active microwave radars, relying upon the same physical mechanisms of electromagnetic wave-sea surface interaction. Sensing the sea surface with different spatial resolutions, they make possible to investigate the horizontal and vertical structure of the MABL from the mesoscale (< 100 km) down to the intermediate (< 10 km) and small (< 2 km) scales. An example of the multi-scale description of the MABL is provided analysing overlapping SAR image and scatterometer wind field in the Mediterranean Sea. Environmental conditions of this case study were characterised by moderate wind (8 to 10 m s −1) and unstable air-sea conditions. The radar backscatter modulations exhibited by the SAR image reveal the presence of largescale atmospheric variations, orographic wind distortions and wind rolls. The majority of the large-scale modulations of radar backscatter are obviously related to the wind speed;some other large-scale feature, which does not seem directly related to the wind, could be explained by the weak Ekman vertical velocity, derived from the scatterometer wind field. The analyses of the wind rolls have been performed through the bi-dimensional spectrum of the SAR image, which shows a two-scale orthogonal wave system with wavelengths of 7 km and 1.5 km. The paper points out the importance of other parameters, such as the sea and air temperatures, in the interpretation of the SAR images and in the full exploitation of the scatterometer winds

Wavelet analysis applied to SAR images to detect atmospheric structures

The aim of this work is to evaluate the possibilities offered by the wavelet analysis in the study of the spatial structure of the radar backscatter, which is linked to the spatial structure of the marine atmospheric boundary layer. Continuous wavelet analysis has been applied to a SAR image of the sea surface, previously analysed by the more classical Conditional Sampling technique. The main problem coped with has been to select, among the large number of wavelet maps produced by the analysis (256), those containing the more energetic backscatter structures. Since the phenomenon imaged by SAR was the convective turbulence, a multiscale and quasi-periodic or intermittent process, a selection of wavelet maps according to their mean energy was unsuccessful. On the contrary, a method based on the calculation of the standard deviation of the less probable highest wavelet amplitudes led to a right selection of the wavelet maps and to a convincing reconstruction of the map of backscatter structures, which resulted similar to that provided through the Conditional Sampling

Towards the wind direction determination in RADARSAT-2 polarimetrie images

AbstractThe interpretation of SAR images of the sea surface is difficult, due to the complexity of the geophysics and of the interaction mechanisms between electromagnetic and sea waves. The determination of the wind direction is crucial for the evaluation of the wind speed, but its retrieval is still an open issue. One of the few methods able to extract the sea surface wind from SAR data only has been developed and extensively applied to Envisat ASAR images in the past years, using the two-dimensional wavelet transform to detect the backscatter signature related to locally coherent wind cells. A preliminary analysis on the applicability of this method to RADARSAT-2 fully polarimetric images has been conducted to verify if polarimetry may improve the detection of backscatter imprints related to the wind direction

Supervised training improves endothelial function measured during induced ischemia in peripheral arterial disease.

Introduction: favorable effect of training on cardiovascular pathology is well documented in literature. Mechanisms evoked are the following: increased NO availability for reduction of oxidative stress, inflammation decrease, improvement of glucidic and lipidic metabolism, resetting of neuro-endocrine balance (1). These mechanism are also involved in the improvement of patients with peripheral arterial disease (PAD) treated with training. PAD is a model of inducible ischemia, in fact claudication is a condition in which ischemia/reperfusion phenomenon is present when walking is conducted till maximum pain (2). This phenomenon may produce a great amount of radical oxygen species with possible consequence on endothelium function. Xanthine oxidase is one of the most relevant enzyme involved in this process. Different types of training are proposed for PAD patients and there is not a consensus whether the ischemic pain should be reached during exercise. So we aimed to verify if maximal treadmill test (till pain) causes endothelial dysfunction, if oxidative stress is acutely aroused and if xanthine oxidase is involved. Therefore we aimed to verify if a training performed under the onset of ischemic pain can improve endothelial function ether at rest and after maximum tolerated exercise. Patients and methods: we enrolled 20 patients with PAD (16 males, 4 females, aged 65-77). Endothelium dependent dilation (EDD) was measured at humeral artery by ultrasound method, before and after maximal treadmill test (speed 3,2 km/h; slope 10%). We administered allopurinol 600 mg the day before and 600 mg 6 hours before a new treadmill test. Serum uric acid and lactate were determined throughout the study. Afterwards patients performed supervised training under pain onset for 20 days with physiotherapist overview. Every 7 days a new treadmill test was performed for updating training distance. At the end of the training period EDD was measured before and after a maximal treadmill test. Furthermore microcirculatory endothelium dependent dilation was measured at the skin of the forefoot by means of laser-Doppler (LD) after iontophoretic acetylcholine administration. Results: maximal treadmill test acutely reduced EDD (6,1\uf0b10,7 vs 9,2\uf0b10,9 %; p<0,05;). Allopurinol improved EDD (10,1\uf0b10,3 vs 9,4\uf0b10,6 %; p<0,05) with a reduced fall after maximal test (delta decrease -21,3\uf0b12,2 vs \u201333,2\uf0b11,2%; p<0,05). Training increased pain free walking distance (131\uf0b112 vs 66,6\uf0b121 m; p<0,05) and absolute walking distance (275\uf0b115 vs 125,8\uf0b140 m; p<0,05). EDD improved after training period (11,3\uf0b10,7 vs 9,2\uf0b10,9; p<0,05). The fall in EDD, observed during maximal treadmill test at the end of training period, was smaller than the one measured before training (delta decrease -15,5\uf0b12,4 vs \u201333,2\uf0b11,2%; p<0,005). Microcirculatory endothelium dependent dilation measured with LD increased after training (table). Table: microcirculatory flux with LD after iontophoretic acetylcholine. Acetylcholine 0,10 mA 10 s 20 s 40 s T 0 (% incr) 35\uf0b19 70\uf0b115 120\uf0b115 T 20 (%incr) 147\uf0b138* 182\uf0b122* 470\uf0b154* (*p<0.005 T20 vs T0) Conclusions: we demonstrate that walking through maximal pain causes impairment of EDD, this is caused by oxidative stress and can be reduced by inhibition of xanthine oxidase. Aerobic training improves EDD and microcirculatory endothelial function, furthermore training reduces the drop of EDD during maximal exercise and increased oxidative stress. As a consequence these results suggest the training should be performed under the maximal pain. References 1. Brendle DC, Joseph LJ, Corretti MC, Gardner AW, Katzel LI. Effects of exercise rehabilitation on endothelial reactivity in older patients with peripheral arterial disease. Am J Cardiol 2001;87:324-9. 2. Andreozzi GM, Leone A, Laudani R, Deinite G, Martini R. Acute impairment of the endothelial function by maximal treadmill exercise in patients with intermittent claudication, and its improvement after supervised physical training. Int Angiol. 2007; 26:12-7

Ascorbic acid prevents vascular dysfunction induced by oral glucose load in healthy subjects

AbstractObjectivesTo examine the effects of oral glucose load on forearm circulatory regulation before and after ascorbic acid administration in healthy subjects.DesignMicrocirculation study with laser Doppler was performed at the hand in basal conditions, after ischemia and after acetylcholine and nitroprusside; strain gauge plethysmography was performed at basal and after ischemia. The tests were repeated in the same sequence 2 hour after oral administration of glucose (75 g). The subjects were randomised for administration of ascorbic acid (1 g bid) or placebo (sodium bicarbonate 1 g bid) for 10 days. After that, the tests were repeated before and after a new oral glucose load. Blood pressure and heart rate were monitored.ResultsMacrocirculatory flux, pressure values and heart rate were unvaried throughout the study. The glucose load caused a reduction in the hyperemic peak flow with laser Doppler and plethysmography; it reduced flux recovery time and hyperemic curve area after ischemia; acetylcholine elicited a minor increase in flux with laser Doppler. The response to nitroprusside was unvaried after glucose load as compared to basal conditions.Treatment with ascorbic acid prevented the decrease in hyperemia after glucose, detected with laser Doppler and plethysmography. Ascorbic acid prevented the decreased response to acetylcholine after glucose, the response to nitroprusside was unaffected by ascorbic acid. Results after placebo were unvaried.ConclusionsOral glucose load impairs endothelium dependent dilation and hyperaemia at microcirculation, probably via oxidative stress; ascorbic acid can prevent it

Wavelet Analysis for Wind Fields Estimation

Wind field analysis from synthetic aperture radar images allows the estimation of wind direction and speed based on image descriptors. In this paper, we propose a framework to automate wind direction retrieval based on wavelet decomposition associated with spectral processing. We extend existing undecimated wavelet transform approaches, by including à trous with B3 spline scaling function, in addition to other wavelet bases as Gabor and Mexican-hat. The purpose is to extract more reliable directional information, when wind speed values range from 5 to 10 ms−1. Using C-band empirical models, associated with the estimated directional information, we calculate local wind speed values and compare our results with QuikSCAT scatterometer data. The proposed approach has potential application in the evaluation of oil spills and wind farms

Training fisico ed attivazione piastrinica in pazienti con claudicatio intermittens: effetti in condizioni di riposo e dopo induzione di ischemia.

Training is a documented effective treatment in patients affected from paripheral arterial disease. Platelet activation plays a pivoltal role in atherosclerosis progression and cardiovascular events. In ischemic heart disease, platelet activation is reduced by aerobic traning, while strenuous execise is associated with enhanced activation. Few data can be found for patients with peripheral arterial disease on training. We aimed to evaluate the effects of aerobic training on platelet activation and oxidative stress at rest and after maximal walking exercise. 18 patients with claudication were enrolled and underwent a 15 days aerobic training period (cycling and treadmill exercise under maximal walking capacity). Platelet function (PAF 100, P selectin) and oxidative stress (malondialdehyde) were analyzed at rest and after maximal treadmill test, at the beginning and at the end of the period. At the end of training absolute walking distance increased, malondialdehyde significantly decreased, P-selectin decreased and epinephrine platelet activation improved. Maximal treadmill test increased ADP platelet activation, while it decrease at the end of training. Aerobic supervised training in patients with peripheral arterial disease improves platelets aggregation, oxidative stress and platelets aggregation during ischemia. These data support and help explaining the benefit of training in atherosclerosis

Storm surge in the Adriatic Sea: observational and numerical diagnosis of an extreme event

International audienceStorm surge events occur in the Adriatic Sea, in particular during autumn and winter, often producing flooding in Venice. Sea levels are forecasted by numerical models, which require wind and pressure fields as input. Their performances depend crucially on the quality of those fields. The storm surge event on 16 November 2002 is analysed and simulated through a finite element hydrodynamic model of the Mediterranean Sea. Several runs were carried out, imposing different atmospheric forcings: wind fields from ECMWF analysis, high resolution winds from the limited area model LAMI and satellite observed winds from QuikSCAT (NASA). The performance of the hydrodynamic model in each case has been quantified. ECMWF fields are effective in reproducing the sea level in the northern Adriatic Sea, if the wind speed is enhanced by a suitable multiplying factor. High resolution winds from LAMI give promising results, permitting an accurate simulation of the sea level maxima. QuikSCAT satellite wind fields produce also encouraging results which claim, however, for further research