Validación con datos in-situ de alturas de ola obtenidas mediante radar altimétrico

Los rádares altimétricos a bordo de satélites artificiales, han sido diseñados para dar información precisa de la altura del nivel del mar, la altura de ola significante y la velocidad del viento sobre la superficie del mar. En los estudios, tanto anteriores como actuales, se observan problemas en las regiones costeras, donde las medidas del altímetro tienen menor precisión y una mayor dificultad a la hora de interpretar estos datos. Estos inconvenientes son debidos a dos factores principales. En primer lugar, la contaminación de la señal radar debido a la cercanía de la costa. En segundo lugar, inexactitudes en las correcciones de marea y troposférica húmeda. A estos problemas se añade la complejidad de la zona de estudio, al ser una región con una amplia gama de procesos hidrodinámicos con diversas escalas espacio-temporales. Tener acceso a información exacta en la costa, con las condiciones que conlleva, tiene una gran importancia debido al enorme interés económico-estratégico de la zona litoral. Este interés hace que surjan nuevas estrategias para generar productos altimétricos optimizados para tales condiciones. Las medidas de la altura de ola significante y su variabilidad en las áreas costeras son usadas para muchos propósitos (por ejemplo, análisis del transporte de sedimento, setup de la ola y tormentas de marea), y para la validación/calibración de modelos (pronóstico de oleaje, circulación oceánica). Estas aplicaciones sirven para un amplio rango de propósitos sociales relevantes, tales como el diseño de estructuras de ingeniería en alta mar, la protección de las zonas costeras, rutas para los buques y la planificación de las operaciones en el océano. Muchos estudios se han dedicado a la validación de los datos de la altura de ola significante dados por el radar altimétrico a bordo de satélites artificiales, utilizando observaciones in-situ. El objetivo de esta ponencia es exponer una metodología para validar los datos de altura de oleaje proporcionados por el radar altimétrico RA-2 a bordo del satélite ENVISAT, a partir de datos in-situ medidos por una boya, y su aplicación a un caso particular

Coastal altimetry products in the Strait of Gibraltar

This paper analyzes the availability and accuracy of coastal altimetry sea level products in the Strait of Gibraltar. All possible repeats of two sections of the Envisat and AltiKa ground-tracks were used in the eastern and western portions of the strait. For Envisat, along-track sea level anomalies (SLAs) at 18-Hz posting rate were computed using ranges from two sources, namely, the official Sensor Geophysical Data Records (SGDRs) and the outputs of a coastal waveform retracker, the Adaptive Leading Edge Subwaveform (ALES) retracker; in addition, SLAs at 1 Hz were obtained from the Centre for Topographic studies of the Ocean and Hydrosphere (CTOH). For AltiKa, along-track SLA at 40 Hz was also computed both from SGDR and ALES ranges. The sea state bias correction was recomputed for the ALES-retracked Envisat SLA. The quality of these altimeter products was validated using two tide gauges located on the southern coast of Spain. For Envisat, the availability of data close to the coast depends crucially on the strategy followed for data screening. Most of the rejected data were due to the radar instrument operating in a low-precision nonocean mode. We observed an improvement of about 20% in the accuracy of the Envisat SLAs from ALES compared to the standard (SGDR) and the reprocessed CTOH data sets. AltiKa shows higher accuracy, with no significant differences between SGDR and ALES. The use of products from both missions allows longer times series, leading to a better understanding of the hydrodynamic processes in the study area

Linking surface and sub-surface variability in Drake Passage

The Antarctic Circumpolar Current (ACC) is the largest current in the world, with a mean transport of 134 Sv, and it provides a significant barrier to the oceanic transfer of heat from mid-latitudes to polar regions. Infrequent full-depth hydrographic sections have shown large variability in the transport of the ACC and the position of its constituent fronts. The many sources of satellite remote-sensing data, with much more frequent sampling, offer another vista on such variability. The question we address here is how the spatial patterns and modes of variability recorded from satellite data relate to the observations from ships. In this paper, we confine our studies to height and temperature data from sensors that are unaffected by clouds, and thus provide near-complete records along the same. The seasonal variations in temperature are deeper south of 60°S, whereas the interannual variations, associated with meandering fronts, occur further north and are deeper. The variability signal from altimetry lies further north again

Improving the analysis of biogeochemical patterns associated with internal waves in the Strait of Gibraltar using remote sensing images

High Amplitude Internal Waves (HAIWs) are physical processes observed in the Strait of Gibraltar (the narrow channel between the Atlantic Ocean and the Mediterranean Sea). These internal waves are generated over the Camarinal Sill (western side of the strait) during the tidal outflow (toward the Atlantic Ocean) when critical hydraulic conditions are established. HAIWs remain over the sill for up to 4 hours until the outflow slackens, being then released (mostly) towards the Mediterranean Sea. These have been previously observed using Synthetic Aperture Radar (SAR), which captures variations in surface water roughness. However, in this work we use high resolution optical remote sensing, with the aim of examining the influence of HAIWs on biogeochemical processes. We used hyperspectral images from the Hyperspectral Imager for the Coastal Ocean (HICO) and high spatial resolution (10 m) images from MultiSpectral Instrument (MSI) on board the Sentinel-2A satellite. This work represents the first attempt to examine the relation between internal wave generation and the water constituents of the Camarinal Sill using hyperspectral and high spatial resolution remote sensing images. This enhanced spatial and spectral resolution revealed the detailed biogeochemical patterns associated with the internal waves and suggests local enhancements of productivity associated with internal waves trains.JRC.D.2-Water and Marine Resource