Synergy within MARSAIS
MARSAIS combines data from SAR sensors with those acquired by either optical or thermal infrared sensors. The aim of this is a better understanding of physical and bio-physical processes in the coastal zone than could be achieved with the help of SAR analysis alone.
Example: Upwelling
Coastal upwelling occurs where waters in the surface layers of the ocean are transported offshore and deep water rises to the surface. Such a process can be initiated by atmospheric forcing or it can be part of a general circulation pattern.
SAR images can show signatures of coastal upwelling due to the wave-current interaction in the convergence zone between upwelled waters and the ambient water mass. With respect to the process creating these signatures (convergence), they are identical to those of convergent current fronts. As a result, upwelling as the cause of the convergence can be difficult to identify.
Synergy of SAR data with images acquired by optical and thermal sensors not only shows the SAR signatures that result from the processes at the front but also the the different properties of the upwelled and ambient water masses on either side of it. Due to the dinstinctly different physical properties of upwelled waters such as a low temperature and high concentrations of nutrients, synergy studies increase the chance of identifying upwelling as the cause of the frontal signatures observed in a coincident SAR image.
While the temperature distribution that can be expected in upwelling regions is very well defined (low temperatures in the upwelling region, higher temperatures of ambient waters), the ocean colour signal can be more variable. The high concentrations of nutrients of upwelled waters are likely to increase primary productivity and thus chlorophyll-a concentration which is commonly used as an indicator of primary production. However, upwelled waters are initially very low in primary production since they originate from depths below the euphotic zone (the surface layer of the ocean that receives sun light). This means that freshly upwelled waters are likely to have a lower rate of primary production compared to the ambient water masses. With some temporal delay, the nutrient rich upwelled waters will then exhibit an increase in primary production and thus a higher level of chlorophyll-a than that of the ambient waters.
Examples:
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The UoS Synergy Toolkit enables joint display and analysis of SAR and other satellite data.