George Wiafe

Satellite Observations of Upwelling in the Gulf of Guinea

The classical case of favorable winds driving coastal upwelling does not adequately account for the upwelling observed along the northwestern Gulf of Guinea (GoG) coast, which is the area of focus in this letter. Herein, we used mainly satellite-derived data to examine the dynamics of upwelling in the study area. Upwelling indexes are derived from sea surface temperature (SST) and wind influences. Low SST, which is a characteristic of upwelling, is observed mainly along the entire coastal region from July to September. The relative contributions of local wind forcing are quantified; the wind-stress-driven Ekman transport was more important than the wind-stress-curl-driven Ekman pumping in affecting changes in SST. They both however do not entirely explain the upwelling that is observed along the entire coast. It is shown that winds in the western equatorial Atlantic force eastward propagating upwelling Kelvin waves that lead to lowering of sea level and SST along the northwestern GoG coast.

Mapping vulnerability and risk of Ghana's coastline to sea level rise

ABSTRACT Coastal erosion and flooding are major threats to coastal dwellers, and the situation is predicted to worsen as a result of the impacts of climate change and associated sea level rise. In order to identify the level of vulnerability of various sections of Ghanas coastline for planning and future hazard management, a coastal vulnerability index approach was adopted for the creation of the relative vulnerability map. The coastal vulnerability variables used include geomorphology, coastal elevation, geology, local subsidence, sea level rise, shoreline change rates, mean tidal range, mean wave height and population density of the coastal areas. Risk factors were assigned to the various variables, and all the factors were combined to calculate the coastal vulnerability for the coastal front of each administrative district along the coast. The outcome was used to produce a vulnerability index map of coastal districts in Ghana. The results revealed that parts of the central coast and the eastern coasts of Ghana were the most vulnerable. It was identified that about 50% of the 540km shoreline of Ghana is vulnerable. This assessment will facilitate the long-term adaptation planning and hazard mitigation to inform the management of Ghanas coast.

Video Oberservation of Waves and Shoreline Change on the Microtidal James Town Beach in Ghana

ABSTRACT Angnuureng, D. B., Almar, R., Appeaning Addo, K., Senechal, N., Castelle, B., Laryea, S. W., Wiafe, G., 2016. Video observation of waves and shoreline change on the microtidal James town Beach in Ghana.. In: Vila-Concejo, A.; Bruce, E.; Kennedy, D.M., and McCarroll, R.J. (eds.), Proceedings of the 14th International Coastal Symposium (Sydney, Australia). Journal of Coastal Research, Special Issue, No. 75, pp. 1022 - 1026, Coconut Creek (Florida), ISSN 0749-0208. The morphology of sandy beaches is highly dynamic. They are influenced by the geology of the coastal area and external hydrodynamic forcing. On long timescales (years to decades), it is more efficient and convenient to monitor beach evolution through remote sensing technics rather than through direct field measurements. Erosion is a major problem along the coastline of Ghana with over 25 erosion hotspots, including James town. Here, tides, ECMWF EraInterim re-analysis wave data and images covering the beach area have been obtained for the 2013–2014 period. This paper presents preliminary results of the first efforts in processing video-derived observations of waves and shoreline change in Ghana. The pilot application shows a strong potential of the video system in providing fair quality wave data for beach management purposes where video wave characteristics are in good agreement with EraInterim global reanalysis (daily RMSE = 0.8 m and 0.7 m for Hb and Tp, respectively). Shorelines extracted from video suggest large monthly variability driven by wave seasonality while shoreline change shows a subsequent erosion/accretion cycle.

Application of RADAR Corner Reflectors for the Detection of Small Vessels in Synthetic Aperture Radar

Detection of vessels from space-based synthetic aperture radar (SAR) data is an important area of research with many applications, including fisheries monitoring, counter-piracy, and maritime border security. The detection of vessels on the ocean surface in SAR imagery requires that the vessel has sufficiently high radar cross section (RCS). In general, the RCS of an object is a function of the objects material, size, and shape, as well as RADAR parameters such as center frequency. Even, two objects of the same size may have different RCSs based on construction materials (i.e., wood versus metal). In Ghana, as in much of the Gulf of Guinea, wooden canoes 6-25 m in length represent a significant percentage of maritime traffic. These canoes are not easy to detect and track in coastal RADAR, nor are they easily detected in SAR imagery. These vessels may represent a significant risk to maritime safety and security. Here, we describe one possible solution for the problem described-above based on inexpensive, versatile corner reflectors with high RCS. Specifically, we describe the design and construction of high RCS corner reflectors and results from a series of experiments in which corner reflectors were installed on wooden canoes. During the experiments, canoes were deployed to specific locations off the coast of Ghana at specific times, corresponding to the acquisition of space-based SAR imagery. We present results from these experiments, which indicate that wooden canoes with these corner reflectors can be detected in space-based SAR imagery.

Development of an algorithm for automatic detection of oil slicks from synthetic aperture radar (SAR) imagery in the Gulf OF Guinea

Pollution in the marine environment caused by oil spills is of great concern to coastal states due to its ecological, environmental and socio-economic impacts. The main objective of this research was to develop an adaptive oil spill detection algorithm for the Gulf of Guinea, and to estimate the location and spatial extent of oil slick in an acquired SAR imagery. The relevance of the use of space borne data for oil slick monitoring is evident in increased vessel traffic and oil drilling activities off the coast of West Africa. Image processing of acquired SAR image of the region involved the application of a median filter, local thresholding, classification, area calculation, and location extraction. Two dark spots were classified as slicks on Radarsat-2 imagery acquired on 18 May, 2008. The information derived from this research is essential for automatic processing and future implementation of oil slick detection and monitoring programme in the Gulf of Guinea.

A novel approach in regional tuna fisheries management using low resolution satellite data: A case study for the Gulf of Guinea

The tuna fisheries in the Gulf of Guinea provides huge economic benefits through fish trade and food security. The region, an important spawning site and migratory path for three dominant tuna species i.e. Skipjack (Katsuwonus pelamis), Yellowfin (Thunnus albacares) and Bigeye (Thunnus obesus), has high incidence of illegal fishing practices, in addition to poor surveillance and monitoring of fisheries resources. Adopting conservation methods for effective management of the tuna fisheries requires an understanding of their thermal preference, foraging behaviour and migratory patterns. Using tuna catch data from 2004 to 2006 in the eastern equatorial Atlantic we have described the spatial distribution of tuna catch and thermal range associated with these distribution from low resolution remotely sensed sea surface temperature data. Tuna in the equatorial Atlantic are concentrated at the major upwelling centers off the coast of Ghana and equatorial Atlantic at surface temperatures of 23 to 28°C.