Characterizing an anticyclone in Western Mediterranean Sea using altimetric data and an eddy tracker

<p>In April 2019, a large anticyclonic Eddy has formed in Western Mediterranean Sea between Sardinia and Balearic Islands. This anticyclone was observable with Sentinel-3 SST satellite data for 7 months and its diameter was estimated to 150 km. Although mesoscale anticyclones are quite common in this part of the Mediterranean Sea, such large and long-live eddies remain exceptional and repercussions for ocean-atmospheric exchanges and for biodiversity might be consequent. However, due to the increase of temperatures during summer, the satellite SST track of the eddy has been lost during a few weeks in August and September. Indeed, the SST signature of the eddy was not distinguishable from surrounding waters anymore. In order to track the eddy during its entire life and have a better understanding of its characteristics, sea level anomaly derived from altimetric data will be analysed in this study with the Py Eddy Tracker toolbox to investigate the variation of its position, its altimetry and its size. The distribution of other remarkable eddies in this zone and period will also be considered. Moreover, a high-resolution SST field will be reconstructed with DINEOF method so the comparison between eddy’s SST and altimetric characteristics will be assured.</p>

Mapping altimetry in the forthcoming SWOT era by back-and-forth nudging a one-layer quasi-geostrophic model

During the past 25 years, altimetric observations of the ocean surface from space have been mapped to provide two dimensional sea surface height (SSH) fields which are crucial for scientific research and operational applications. The SSH fields can be reconstructed from conventional altimetric data using temporal and spatial interpolation. For instance, the standardDUACS products are created with an optimal interpolation method which is effective for both low temporal and low spatial resolution. However, the upcoming next-generation SWOT mission will provide very high spatial resolution but with low temporal resolution.The present paper makes the case that this temporal-spatial discrepancy induces the need for new advanced mapping techniques involving information on the ocean dynamics. An algorithm is introduced, dubbed the BFN-QG, that uses a simple data assimilation method, the back-and-forth nudging, to interpolate altimetric data while respecting quasigeostrophic dynamics. The BFN-QG is tested in an observing system simulation experiments and compared to the DUACS products. The experiments consider as reference the high-resolution numerical model simulation NATL60 from which are produced realistic data: four conventional altimetric nadirs and SWOT data. In a combined nadirs and SWOT scenario, the BFN-QG substantially improves the mapping by reducing the root-mean-square errors and increasing the spectral effective resolution by 40km. Also, the BFN-QG method can be adapted to combine large-scale corrections from nadirs data and small-scale corrections from SWOT data so as to reduce the impact of SWOT correlated noises and still provide accurate SSH maps.

Fluvial environmental disasters: risk perception and evaluation of government responses by riverine populations in Cacau Pirêra, Iranduba/AM

This article unveils the perceptions of vulnerable populations of the Amazon regarding the risks of river disasters and highlights their assessment of the effectiveness of government responses. The record of perceptions, assessments and identification of social vulnerabilities were obtained in interviews with focus groups formed by residents of Cacau Pirêra, in the Amazon. To characterize the environmental threats and vulnerabilities, fluviometric and altimetric data of the occupied areas were used. In that District, floods do not have to exceed normal limits to constitute environmental disasters and, in the perception of residents, pose more risks than ebb. Participants point to the low effectiveness of public policies as the main cause of the ineffectiveness of the government's response to water disasters. Natural disaster studies should consider the interactions between the environmental and social aspects of territories to reach an understanding of the complexity of the context in which they occur.

Methodology for classification of land use and vegetation cover using MODIS-EVI data

ABSTRACT This study aimed to verify the applicability of using MODIS-EVI sensor time series for land use and vegetation cover mapping in the Pampa biome, Rio Grande do Sul state, Brazil. The study period comprised the months from June 2013 to June 2014. The procedures included the use of MODIS Sensor images, altimetric data and nighttime images, associated with a hierarchical decision tree classifier, constructed using the C4.5 algorithm. The proposed approach stems from the consideration that the study area has varying characteristics and, therefore, should be treated simultaneously by different and intuitive classifiers, which justifies the choice of decision tree. To evaluate the results, reference data acquired from Landsat 8-OLI satellite images and IBGE data were used. The classification using the MODIS time series showed a global accuracy of 90.09% and Kappa index of 0.8885. When compared to the IBGE reference data, the Soybean class obtained a correlation coefficient of 0.94, the rice class obtained 0.97 and the silviculture class obtained the lowest value, 0.78. The highest spectral similarities were found in the vegetation cover classes, such as grassland, forest and silviculture. Therefore, with the use of multitemporal data from the MODIS sensor, combined with the use of altimetric data and nighttime images, it is possible to generate a land use and vegetation cover map for the Pampa biome with an acceptable accuracy, considering the MODIS sensor resolution limitations.

Estudo da obtenção do nível médio do mar com altimetria por satélites

The shape attributed to the Earth, by convention, is the geoid. This is considered as the equipotential surface which coincides with the undisturbed Mean Level of the Seas (MSL). It is of fundamental importance to geodesists determining the MSL (altimetric Data), since this play an important role in the realization of global reference systems and enable the integration of data referred to classic vertical networks, where each datum is defined by the MSL. Currently altimetry satellite (ALTSAT) is an effective technique for monitoring the MSL, as it provides a methodical and continuous data collection and that in turn allows the global observation of the sea level (SL). Resulting in a data structure with several oceanographic parameters and time series of consistent data for long periods. This greatly facilitates the use of these data for studies of NMM and, hence, the determining of the Mean Dynamic Topography (MDT) and geoid itself. This paper focuses on the study of obtaining MSL obtained by altimetry missions, focusing on TOPEX/Poseidon, Jason-1, Jason-2 and Jason-3 satellites aiming the importance of MSL for MDT determination.