9 The Upwelling Area Off Namibia, the Northern Part of the Benguela Current System
171
board the Terra (EOS AM) and Aqua (EOS PM) satellites. Both instruments and their
level-2 products have a spatial resolution of 1 km and cover the entire Earth every 1–3
days. MERIS was operated until April 2012 by the European Space Agency (ESA)
on board the Environmental Satellite (Envisat) covering the earth in 3 days. The Full
Resolution (FR) and the Reduced Resolution (RR) products had spatial resolutions
of 300 m and 1200 m, respectively. True colour images derived from MODIS and
MERIS high resolution data (250 m and 300 m spatial resolution) are implemented
for detailed studies of filaments.
Broad band data of higher spatial resolution of both the Landsat 7 Enhanced
Thematic Mapper (ETM+) and SPOT were implemented to investigate the structure of coastal sulphur plumes. The visible channels of ETM+ and SPOT have
a spatial resolution of 30 m and 20 m, respectively, and the repetition rates of 16
and 23 days allowed only case studies. Wind and sea level data were derived from
Topex/Poseidon, the TRMM Microwave Imager (TMI), where TRMM stands for the
Tropical Rainfall Measuring Mission satellite, the AMSR-E (Advanced Microwave
Scanning Radiometer—Earth Observing System on MODIS Aqua, or the SeaWinds
Scatterometer on QuikBird (later dubbed QuikSCAT).
9.4 Bio-Optical Characterisation of the Area
The described features resulting from oceanographic processes cause high variability
in bio-optical properties. Chlorophyll-a concentrations between 0.5 and 18 mg m
−3
were presented for the area south of Walvis Bay for austral winter and spring (Barlow
et al. 2001; Barlow et al. 2006). In situ measurements of optically active water
constituents were performed during two cruises in 2003 and 2004 (Ohde et al. 2007;
Siegel et al. 2007). Chlorophyll-a, Suspended Particulate Matter (SPM) and Coloured
Dissolved Organic Matter (CDOM) were characterised by strong gradients from the
open sea to the coast. Chlorophyll-a varied between 0.3 and 42 mg m
−3 partly also
with a high portion of phaeopigment, an indicator for degradation of chlorophyll-a.
Similar patterns were measured for SPM ranging from 1.1 to 24 g m
−3 and for the
absorption by CDOM measured at 440 nm from 0.06 to 0.5 m
−1 . These variations
in the concentration of optically active water constituents strongly influence the
transparency and water colour. Secchi disc depth as measure of water transparency
varied between 2.8 m and 32.5 m. The measured spectral reflectances quantify the
differences in water colour (Fig. 9.3).
The reflectance of clear open ocean water is characterised by a reflectance maximum in the blue spectral range. In blue green waters the maximum shifted to
480–500 nm. Coastal stations were characterized by very turbid brownish water
with reflectance maxima between 550 and 580 nm. This was old productive water
with high amount of chlorophyll-a, but also with high concentration of degradation
products such as detritus and CDOM. The absorption of phytoplankton decreases
the reflectance in the blue and red spectral range because of their absorption maxima
around 440 nm and 674 nm. The absorption in the short wavelength range is also
171
board the Terra (EOS AM) and Aqua (EOS PM) satellites. Both instruments and their
level-2 products have a spatial resolution of 1 km and cover the entire Earth every 1–3
days. MERIS was operated until April 2012 by the European Space Agency (ESA)
on board the Environmental Satellite (Envisat) covering the earth in 3 days. The Full
Resolution (FR) and the Reduced Resolution (RR) products had spatial resolutions
of 300 m and 1200 m, respectively. True colour images derived from MODIS and
MERIS high resolution data (250 m and 300 m spatial resolution) are implemented
for detailed studies of filaments.
Broad band data of higher spatial resolution of both the Landsat 7 Enhanced
Thematic Mapper (ETM+) and SPOT were implemented to investigate the structure of coastal sulphur plumes. The visible channels of ETM+ and SPOT have
a spatial resolution of 30 m and 20 m, respectively, and the repetition rates of 16
and 23 days allowed only case studies. Wind and sea level data were derived from
Topex/Poseidon, the TRMM Microwave Imager (TMI), where TRMM stands for the
Tropical Rainfall Measuring Mission satellite, the AMSR-E (Advanced Microwave
Scanning Radiometer—Earth Observing System on MODIS Aqua, or the SeaWinds
Scatterometer on QuikBird (later dubbed QuikSCAT).
9.4 Bio-Optical Characterisation of the Area
The described features resulting from oceanographic processes cause high variability
in bio-optical properties. Chlorophyll-a concentrations between 0.5 and 18 mg m
−3
were presented for the area south of Walvis Bay for austral winter and spring (Barlow
et al. 2001; Barlow et al. 2006). In situ measurements of optically active water
constituents were performed during two cruises in 2003 and 2004 (Ohde et al. 2007;
Siegel et al. 2007). Chlorophyll-a, Suspended Particulate Matter (SPM) and Coloured
Dissolved Organic Matter (CDOM) were characterised by strong gradients from the
open sea to the coast. Chlorophyll-a varied between 0.3 and 42 mg m
−3 partly also
with a high portion of phaeopigment, an indicator for degradation of chlorophyll-a.
Similar patterns were measured for SPM ranging from 1.1 to 24 g m
−3 and for the
absorption by CDOM measured at 440 nm from 0.06 to 0.5 m
−1 . These variations
in the concentration of optically active water constituents strongly influence the
transparency and water colour. Secchi disc depth as measure of water transparency
varied between 2.8 m and 32.5 m. The measured spectral reflectances quantify the
differences in water colour (Fig. 9.3).
The reflectance of clear open ocean water is characterised by a reflectance maximum in the blue spectral range. In blue green waters the maximum shifted to
480–500 nm. Coastal stations were characterized by very turbid brownish water
with reflectance maxima between 550 and 580 nm. This was old productive water
with high amount of chlorophyll-a, but also with high concentration of degradation
products such as detritus and CDOM. The absorption of phytoplankton decreases
the reflectance in the blue and red spectral range because of their absorption maxima
around 440 nm and 674 nm. The absorption in the short wavelength range is also