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T. J. Ballatore et al.
20.1 Introduction
The idea of remote sensing—the art and science of obtaining information about an
object without being in physical contact with the object (Jensen 2007)—is in many
ways the holy grail of lake management. The potential to look wide and often at
conditions in a given lake has spurred much interest, resulting in a burgeoning body
of research and applications including recent work by Gower et al. (2005), RuizVerdú et al. (2008), Chipman et al. (2009), Gitelson et al. (2011), Bradt (2012) and
Matthews et al. (2012).
The potential offered by remote sensing is particularly attractive in Africa where
administrative capacity to carry out field-based monitoring is limited. Lake managers
in Africa are confronted with a task of monitoring lakes that would challenge even
the most well-funded monitoring programs.
Here, we review the applications of remote sensing to African lakes as described
in the scientific literature. The applications are surprisingly broad: spatially, they
include 29 lakes that cover all corners of the continent (see Fig. 20.1); thematically,
they range from passive to active sensors looking at both water quantity and quality.
Overall, we find it convenient to divide the applications into two broad categories:
those that look at the amount of water in a given lake and those that look at the
properties of that water. The former category include studies that measure lake area
through (1) visible and near-infrared (NIR) sensing of lake extent/shoreline, (2)
thermal sensing of inundated areas, and (3) microwave sensing of water under cloud
cover. They also include studies that examine lake level through (4) altimetric and
(5) gravimetric observations. The latter category includes work on strictly physical
aspects such as (6) thermal sensing for lake surface temperature as well as biological
aspects such as (7) visible and NIR sensing of macrophytes and (8) microwave
sensing of macrophytes and perhaps the most widely known application—(9) optical
sensing of trophic conditions through measurement of chlorophyll-a, euphotic depth
and a range of related indicators.
Few of the studies reviewed here fall solely into one of the above nine categories;
most papers make use of a combination of techniques. For example, a paper using
altimetric observations to estimate changes in lake level might also rely on visible
and NIR imagery to confirm lake area (and hence, level) changes.
More importantly, it must be noted that remote sensing does not completely obviate the need for field observations and traditional sampling programs. In fact, most
of the methods described here still require, or greatly benefit from, calibration with
actual measurements taken in the field concurrent with the remotely-sensed images.
Nevertheless, as the literature demonstrates, and as we explore in the discussion,
remote sensing can indeed provide a wealth of information to greatly aid the work of
those concerned with lake management in local communities, national governments
and international organizations throughout Africa.
T. J. Ballatore et al.
20.1 Introduction
The idea of remote sensing—the art and science of obtaining information about an
object without being in physical contact with the object (Jensen 2007)—is in many
ways the holy grail of lake management. The potential to look wide and often at
conditions in a given lake has spurred much interest, resulting in a burgeoning body
of research and applications including recent work by Gower et al. (2005), RuizVerdú et al. (2008), Chipman et al. (2009), Gitelson et al. (2011), Bradt (2012) and
Matthews et al. (2012).
The potential offered by remote sensing is particularly attractive in Africa where
administrative capacity to carry out field-based monitoring is limited. Lake managers
in Africa are confronted with a task of monitoring lakes that would challenge even
the most well-funded monitoring programs.
Here, we review the applications of remote sensing to African lakes as described
in the scientific literature. The applications are surprisingly broad: spatially, they
include 29 lakes that cover all corners of the continent (see Fig. 20.1); thematically,
they range from passive to active sensors looking at both water quantity and quality.
Overall, we find it convenient to divide the applications into two broad categories:
those that look at the amount of water in a given lake and those that look at the
properties of that water. The former category include studies that measure lake area
through (1) visible and near-infrared (NIR) sensing of lake extent/shoreline, (2)
thermal sensing of inundated areas, and (3) microwave sensing of water under cloud
cover. They also include studies that examine lake level through (4) altimetric and
(5) gravimetric observations. The latter category includes work on strictly physical
aspects such as (6) thermal sensing for lake surface temperature as well as biological
aspects such as (7) visible and NIR sensing of macrophytes and (8) microwave
sensing of macrophytes and perhaps the most widely known application—(9) optical
sensing of trophic conditions through measurement of chlorophyll-a, euphotic depth
and a range of related indicators.
Few of the studies reviewed here fall solely into one of the above nine categories;
most papers make use of a combination of techniques. For example, a paper using
altimetric observations to estimate changes in lake level might also rely on visible
and NIR imagery to confirm lake area (and hence, level) changes.
More importantly, it must be noted that remote sensing does not completely obviate the need for field observations and traditional sampling programs. In fact, most
of the methods described here still require, or greatly benefit from, calibration with
actual measurements taken in the field concurrent with the remotely-sensed images.
Nevertheless, as the literature demonstrates, and as we explore in the discussion,
remote sensing can indeed provide a wealth of information to greatly aid the work of
those concerned with lake management in local communities, national governments
and international organizations throughout Africa.