19 Satellite Surveys of Lagoon and Coastal Waters . . .
381
(Bosc et al. 2004; Volpe et al. 2007; Barale et al. 2008). Analogous applications,
using high-sensitivity sensors that collect data at low spatial resolution (at km scale)
but medium spectral resolution (∼10’s of nm), geared to measure indicators like
concentration of chlorophyll-like pigments (CHL) or total suspended matter (TSM)
in marine waters, have been developed also for lake studies (Zilioli 2001).
Low-sensitivity sensors working in the visible and near-infrared parts of the
spectrum, with higher spatial resolution (at dm scale) but lower spectral resolution
(∼100’s of nm), are primarily designed for detecting land features. However, current
instruments and processing algorithms provide better performance for aquatic studies than ever previously available (Kloiber et al. 2002; Sawaya et al. 2003). Thus,
monitoring programs of inland waters have been conducted using land observation
sensors as well, with the obvious advantage of data on multiple small lakes being
collected quickly and relatively inexpensively, reducing the effort and cost of field
sampling. Such programs have shown good correlations between RS data and in situ
measurements of Secchi Disk Transparency (SDT), Colored Dissolve Organic Matter (CDOM), or CHL and TSM (Lathrop 1992; Dewider and Khedr 2001; Brezonik
et al 2005). However, it is in the assessment of structural properties, e.g. varying
water surface area or aquatic vegetation cover, that sensors borrowed from landobservation programs can best exploit their combined spatial and spectral potential
(Hess et al. 2003; Ozemi and Bauer 2004; Cozar et al. 2005; Ahmed et al. 2009).
As for the region of interest here, Barale and Folving (1996) gave early examples
of studying coastal runoff by satellite RS, looking at the fluvial and marine interactions that occur within the area off the Nile river delta. More recently, Dewidar and
Khedr (2005) combined satellite and surface measurements to map surface water
parameters, and multiple linear regression models to prepare digital cartographic
products depicting water quality over large areas. Over the past decade, Ahmed et al.
(2000, 2001, 2003, 2007, 2009) used RS techniques for repeated bio-geo-chemical
assessments of the Egyptian lagoons, and Geographic Information System (GIS)
techniques to produce spatial distribution maps of their properties. In particular,
Ahmed (2003) applied change analysis methods to sequences of satellite images, in
order to identify modifications that have occurred both inside and outside the coastal
lagoons, documenting variations of water areas, as well as erosion and accretion
processes along the lagoon openings.
In the following, the use of RS to identify key environmental features of enclosed
and near-coastal water bodies of northern Egypt, in the southeastern Mediterranean
region, will be reviewed. Examples will be given of sensors, techniques, parameters
and applications available to monitor the status and evolution of lagoon and coastal
waters, and to describe some of their basic ecological problems. An evaluation of
changes that have occurred in the lagoons, as well as the recent trends along the
adjacent coastlines, will be proposed. Finally, GIS descriptions of lagoon size, vegetation patterns and land cover/use, will be presented, to show how elements for
environmental management purposes can be derived from RS data.
381
(Bosc et al. 2004; Volpe et al. 2007; Barale et al. 2008). Analogous applications,
using high-sensitivity sensors that collect data at low spatial resolution (at km scale)
but medium spectral resolution (∼10’s of nm), geared to measure indicators like
concentration of chlorophyll-like pigments (CHL) or total suspended matter (TSM)
in marine waters, have been developed also for lake studies (Zilioli 2001).
Low-sensitivity sensors working in the visible and near-infrared parts of the
spectrum, with higher spatial resolution (at dm scale) but lower spectral resolution
(∼100’s of nm), are primarily designed for detecting land features. However, current
instruments and processing algorithms provide better performance for aquatic studies than ever previously available (Kloiber et al. 2002; Sawaya et al. 2003). Thus,
monitoring programs of inland waters have been conducted using land observation
sensors as well, with the obvious advantage of data on multiple small lakes being
collected quickly and relatively inexpensively, reducing the effort and cost of field
sampling. Such programs have shown good correlations between RS data and in situ
measurements of Secchi Disk Transparency (SDT), Colored Dissolve Organic Matter (CDOM), or CHL and TSM (Lathrop 1992; Dewider and Khedr 2001; Brezonik
et al 2005). However, it is in the assessment of structural properties, e.g. varying
water surface area or aquatic vegetation cover, that sensors borrowed from landobservation programs can best exploit their combined spatial and spectral potential
(Hess et al. 2003; Ozemi and Bauer 2004; Cozar et al. 2005; Ahmed et al. 2009).
As for the region of interest here, Barale and Folving (1996) gave early examples
of studying coastal runoff by satellite RS, looking at the fluvial and marine interactions that occur within the area off the Nile river delta. More recently, Dewidar and
Khedr (2005) combined satellite and surface measurements to map surface water
parameters, and multiple linear regression models to prepare digital cartographic
products depicting water quality over large areas. Over the past decade, Ahmed et al.
(2000, 2001, 2003, 2007, 2009) used RS techniques for repeated bio-geo-chemical
assessments of the Egyptian lagoons, and Geographic Information System (GIS)
techniques to produce spatial distribution maps of their properties. In particular,
Ahmed (2003) applied change analysis methods to sequences of satellite images, in
order to identify modifications that have occurred both inside and outside the coastal
lagoons, documenting variations of water areas, as well as erosion and accretion
processes along the lagoon openings.
In the following, the use of RS to identify key environmental features of enclosed
and near-coastal water bodies of northern Egypt, in the southeastern Mediterranean
region, will be reviewed. Examples will be given of sensors, techniques, parameters
and applications available to monitor the status and evolution of lagoon and coastal
waters, and to describe some of their basic ecological problems. An evaluation of
changes that have occurred in the lagoons, as well as the recent trends along the
adjacent coastlines, will be proposed. Finally, GIS descriptions of lagoon size, vegetation patterns and land cover/use, will be presented, to show how elements for
environmental management purposes can be derived from RS data.