56
N. Hoepffner et al.
of the four major upwelling areas of the world ocean, the Benguela system in the
south and the Morocco-Mauritanian system in the north (Hill et al. 1998). These
are sites of economical importance due to high water productivity sustaining large
biodiversity and valuable fish resources. Also, a number of mesoscale structures and
oceanic fronts are recurrent e.g. along the eastern coast of Africa molding to a large
extent the pelagic ecosystem and species distribution.
Due to this dynamic, coastal and marine environments play a vital role in the
economy and society of many African countries (Odada 2010), contributing significantly to reducing the national balance of payments deficit, creating employment and
meeting the protein needs of the local population. Fish products provide more than
60 % of the dietary proteins in many countries, such as Ghana and Gambia, stressing
the need to develop fisheries management strategies to ensure efficient exploitation
while keeping the stocks sustainable on the long-term. Given that marine physics
can determine to a large extent the rate and distribution of the biological resources
across a range of scales (Gargett 1997), monitoring the dynamics of water masses
at appropriate resolution in the time-space domain will considerably facilitate the
formulation and implementation of these strategies, as well as the mitigation of an
increasing human impact on marine and coastal resources around Africa.
Earth Observations (EO) from satellite enable the provision of environmental
information at low cost (to the users) and unprecedented time scales over large and
distant areas of the oceans, complementing expensive, hence scarce, field campaigns
using research vessels. Thermal Infrared (TIR) sensors on-board satellites, depicting
changes in Sea Surface Temperature (SST) over large marine areas, are instrumental
to monitor variations in the water masses at the ocean surface resulting from long or
short-term atmospheric processes, as well as water column dynamics.
In the following, the applications of TIR to monitor and assess different marine
issues around Africa are reviewed. A first section summarizes the fundamental basis to measure TIR signal over the ocean from space, listing the main sensors and
databases available, and outlining the current status with the use of TIR data for accurate retrieval of SST. Other sections are referring to different applications of TIR
over African coastal and marine waters, using SST as a single indicator of changes in
water masses or in combination with other platforms to assess important processes
such as fisheries. Finally, some concluding remarks are presented, providing a forward perspective in the use of TIR imagery to meet the societal needs of the African
population in the context of international aid initiatives.
3.2 Sensors and Data Repositories
Quantitative information about the oceans is transferred from the sea surface to the
satellite sensor through the atmosphere via electromagnetic radiation. This information transfer has some constraints, which are set by the relationship between the
radiation emitted from the sea surface, and the atmosphere it travels through before
reaching the satellite sensor. Thermal Infrared (TIR) sensors usually passively collect
radiations at wavelengths between ca. 10 to 15 μm, although some instruments have
N. Hoepffner et al.
of the four major upwelling areas of the world ocean, the Benguela system in the
south and the Morocco-Mauritanian system in the north (Hill et al. 1998). These
are sites of economical importance due to high water productivity sustaining large
biodiversity and valuable fish resources. Also, a number of mesoscale structures and
oceanic fronts are recurrent e.g. along the eastern coast of Africa molding to a large
extent the pelagic ecosystem and species distribution.
Due to this dynamic, coastal and marine environments play a vital role in the
economy and society of many African countries (Odada 2010), contributing significantly to reducing the national balance of payments deficit, creating employment and
meeting the protein needs of the local population. Fish products provide more than
60 % of the dietary proteins in many countries, such as Ghana and Gambia, stressing
the need to develop fisheries management strategies to ensure efficient exploitation
while keeping the stocks sustainable on the long-term. Given that marine physics
can determine to a large extent the rate and distribution of the biological resources
across a range of scales (Gargett 1997), monitoring the dynamics of water masses
at appropriate resolution in the time-space domain will considerably facilitate the
formulation and implementation of these strategies, as well as the mitigation of an
increasing human impact on marine and coastal resources around Africa.
Earth Observations (EO) from satellite enable the provision of environmental
information at low cost (to the users) and unprecedented time scales over large and
distant areas of the oceans, complementing expensive, hence scarce, field campaigns
using research vessels. Thermal Infrared (TIR) sensors on-board satellites, depicting
changes in Sea Surface Temperature (SST) over large marine areas, are instrumental
to monitor variations in the water masses at the ocean surface resulting from long or
short-term atmospheric processes, as well as water column dynamics.
In the following, the applications of TIR to monitor and assess different marine
issues around Africa are reviewed. A first section summarizes the fundamental basis to measure TIR signal over the ocean from space, listing the main sensors and
databases available, and outlining the current status with the use of TIR data for accurate retrieval of SST. Other sections are referring to different applications of TIR
over African coastal and marine waters, using SST as a single indicator of changes in
water masses or in combination with other platforms to assess important processes
such as fisheries. Finally, some concluding remarks are presented, providing a forward perspective in the use of TIR imagery to meet the societal needs of the African
population in the context of international aid initiatives.
3.2 Sensors and Data Repositories
Quantitative information about the oceans is transferred from the sea surface to the
satellite sensor through the atmosphere via electromagnetic radiation. This information transfer has some constraints, which are set by the relationship between the
radiation emitted from the sea surface, and the atmosphere it travels through before
reaching the satellite sensor. Thermal Infrared (TIR) sensors usually passively collect
radiations at wavelengths between ca. 10 to 15 μm, although some instruments have