Modélisation de l'évolution spatiale et temporelle de l'épaisseur optique des aérosols à l'échelle régionale

Monitoring of aerosol optical depth (AOD) is of particular importance due to the significant role of aerosols in the atmospheric radiative budget. AOD is a key parameter in studies related to global climatology, atmospheric pollutants, forest fires, and for performing atmospheric corrections on remotely sensed imagery of surface scenes. We attempt to fill gaps in spatio-temporal AOD measurements using a new methodology that links AOD measurements and particulate matter Transport Model (TM) using a data assimilation approach. This new modelling package (AODSEM for A[barbelow]erosol O[barbelow]ptical D[barbelow]epth S[barbelow]patiotemporal E[barbelow]volution M[barbelow]odel) uses a size and aerosol type segregated semi-Lagrangian-Eulerian trajectory algorithm driven by analysed meteorological data. Its novelty resides in the fact that the model evolution is tied to available AOD measurements and all physical processes have been optimized to track this important but crude parameter. We present in this paper a sensitiviity study to AODSEM's important parameters or processes (spatial and temporal resolution, hygroscopic effects, spin-up time, precipitations, size distribution). We also present the first validation results for this new model applied to North America during June 1997 and august 1998. The results show the potential of this approach especially when used with remotely sensed AOD. Residuals between AODSEM analysis and measurements are smaller than typical errors associated to remotely sensed AOD. AODSEM also give better results than classical interpolation schemes. This result is especially evident when the available number of AOD measurements is small. Our results shows that AODSEM can be efficient to correct for error induced by simplifications in the physical parametrization and by error in emission inventories. Our results also shows that in the context of low polluted zone and period, AODSEM can be used to provide AOD spatio-temporal forecasts. In that case, correlation between AODSEM and independent AERONET data can reach r = 0,86 with a mean residual of [left angle bracket][delta]T[subscript a] [right angle bracket] = 0,02 and [sigma] = 0,04. For a specific pollution event, AOD forecast can also be achieved when an episodic emission inventory is available"--Résumé abrégé par UMI

Remote sensing of aerosols at night with the CoSQM sky brightness data

Aerosol optical depth is an important indicator of aerosol particle properties and their associated radiative impacts. AOD determination is very important to achieve relevant climate modelling. Most remote sensing techniques to retrieve aerosol optical depth are applicable to daytime given the high level of light available. The night represents half of the time but in such conditions only a few remote sensing methods are available. Among these approaches, the most reliable are moon photometers and star photometers. In this paper, we attempt to fill gaps in the aerosol detection performed with the aforementioned techniques using night sky brightness measurements during moonless nights with the novel CoSQM, a portable, low-cost and open-source multispectral photometer. In this paper, we present an innovative method for estimating the aerosol optical depth using an empirical relationship between the zenith night sky brightness measured at night with the CoSQM and the aerosol optical depth retrieved during daytime from the AErosol Robotic NETwork

Magnitude to luminance conversions and visual brightness of the night sky

The visual brightness of the night sky is not a single-valued function of its brightness in other photometric bands, because the transformations between photometric systems depend on the spectral power distribution of the skyglow. We analyze the transformation between the night sky brightness in the Johnson-Cousins V band (mV, measured in magnitudes per square arcsecond, mpsas) and its visual luminance (L, in SI units cd m^(-2) ) for observers with photopic and scotopic adaptation, in terms of the spectral power distribution of the incident light. We calculate the zero-point luminances for a set of skyglow spectra recorded at different places in the world, including strongly light-polluted locations and sites with nearly pristine natural dark skies. The photopic skyglow luminance corresponding to m_(v)=0.00 mpsas is found to vary between 1.11-1.34 x 10^(5) cd m^(-2) if m_(v) is reported in the absolute (AB) magnitude scale, and between 1.18-1.43 x 10^(5) cd m^(-2) if a Vega scale for m_(v) is used instead. The photopic luminance for m_(v)=22.0 mpsas is correspondingly comprised between 176 and 213 µcd m^(-2) (AB), or 187 and 227 µcd m^(-2) (Vega). These constants tend to decrease for increasing correlated color temperatures (CCT). The photopic zero-point luminances are generally higher than the ones expected for blackbody radiation of comparable CCT. The scotopic-to-photopic luminance ratio (S/P) for our spectral dataset varies from 0.8 to 2.5. Under scotopic adaptation the dependence of the zero-point luminances with the CCT, and their values relative to blackbody radiation, are reversed with respect to photopic ones

Assessing light pollution in vast areas: zenith sky brightness maps of Catalonia

Zenith sky brightness maps in the V and B bands of the region of Catalonia are presented in this paper. For creating them we have used the light pollution numerical model Illumina v2. The maps have a sampling of 5x5 km for the whole region with an improved resolution of 1x1 km for one of the provinces within Catalonia, Tarragona. Before creating the final maps, the methodology was tested successfully by comparing the computed values to measurements in nineteen different locations spread out throughout the territory. The resulting maps have been compared to the zenith sky brightness world atlas and also to Sky Quality Meter (SQM) dynamic measurements. When comparing to measurements we found small differences mainly due to mismatching in the location of the points studied, and also due to differences in the natural sky brightness and atmospheric content. In the comparison to the world atlas some differences were expected as we are taking into account the blocking effect of topography and obstacles, and also due to a more precise light sources characterization. The results of this work confirm the conclusion found in other studies that the minimum sampling for studying sky brightness fine details is of 1x1 km. However, a sampling of 5x5 km is interesting when studying general trends, mainly for vast areas, due to the reduction of the time required to create the maps.Comment: 32 pag, 17 figure

Evaluating human photoreceptoral inputs from night-time lights using RGB imaging photometry

Night-time lights interact with human physiology through different pathways starting at the retinal layers of the eye; from the signals provided by the rods; the S-, L- and M-cones; and the intrinsically photosensitive retinal ganglion cells (ipRGC). These individual photic channels combine in complex ways to modulate important physiological processes, among them the daily entrainment of the neural master oscillator that regulates circadian rhythms. Evaluating the relative excitation of each type of photoreceptor generally requires full knowledge of the spectral power distribution of the incoming light, information that is not easily available in many practical applications. One such instance is wide area sensing of public outdoor lighting; present-day radiometers onboard Earth-orbiting platforms with sufficient nighttime sensitivity are generally panchromatic and lack the required spectral discrimination capacity. In this paper, we show that RGB imagery acquired with off-the-shelf digital single-lens reflex cameras (DSLR) can be a useful tool to evaluate, with reasonable accuracy and high angular resolution, the photoreceptoral inputs associated with a wide range of lamp technologies. The method is based on linear regressions of these inputs against optimum combinations of the associated R, G, and B signals, built for a large set of artificial light sources by means of synthetic photometry. Given the widespread use of RGB imaging devices, this approach is expected to facilitate the monitoring of the physiological effects of light pollution, from ground and space alike, using standard imaging technology

Post-treatment MRI aspects of photodynamic therapy for prostate cancer

OBJECTIVES: Photodynamic therapy is a new focal therapy for prostate cancer. METHODS: In this technique, a photosensitising agent is introduced intravenously, then activated by local laser illumination to induce tumour necrosis. Treatment efficacy is assessed by magnetic resonance imaging (MRI). RESULTS AND CONCLUSIONS: We illustrate specific post-treatment MRI aspects at early and late follow-up with pathological correlations. TEACHING POINTS: Dynamic phototherapy is a new and promising focal therapy for prostate cancer. One-week MRI shows increased volume of the treated lobe and large, homogeneous necrosis area. Six-month MRI shows significant changes of the prostate shape and signal. Six-month MRI becomes "base line" appearance for further follow-up or monitoring

Prostatic artery embolization for intractable hematuria in patients with unregulated coagulation parameters: three case reports

Introduction: Benign prostatic hyperplasia is a prevalent disease that could be responsible of severe intractable hematuria requiring invasive surgical management. Case presentation: We report three high-risk cases presented with intractable hematuria of prostatic origin with high medical co-morbidities treated safely and effectively by prostatic artery embolization with favorable outcomes. Conclusions: In non-surgical, anticoagulated patients, prostatic artery embolization represents a safe and effective intervention for the treatment of intractable hematuria related to benign prostatic hyperplasia