section, we explore the differences between aerial photography and satellite imagery
and while focusing on the advancements in remote sensing technologies over the past
10 years. Challenges presented by the sensors are described at the end of this section.
3.1 AERIAL PHOTOGRAPHY VERSUS DIGITAL IMAGERY
Aerial photography lags behind digital imagery in several areas, especially in
multi-variable image extraction capabilities, but its comparatively lower cost and
simple technology are particularly attractive when mapping reef environments in
developing countries (Table 3). Aerial photography has been successful in mapping
structural loss (Lewis, 2002), reef extent (Thamrongnawasawat and Hopley, 1994), and
benthic communities (Cuevas-Jimenez and Ardisson, 2002). It has also been used as a
tool for proactive management (Riegl and Piller, 2000). Generally, an aerial
photograph is considered successful at mapping when (1) the spatial resolution of the
map or image conforms to the complexity of the environment so that details of most
interest are revealed; (2) the film is sensitive to wavelengths that penetrate the
overlying water and illuminate the architecturally complex bottom structure; and (3) the
final product is reliable (Chauvaud et al., 1998). With the overwhelming volume of
archived, available aerial photography, there is a trend towards integrating digitized
aerial photographs with digital imagery to improve the delineation of features and, thus,
image accuracy (Green et al., 2000).
Table 3. Comparison between aerial photography and digital imagery of shallow-water coral
reef areas. (Compiled from Chauvaud et al., 1998, Mumby et al., 1997, and Sheppard et al.,
1995)
Issues
Aerial Photography
Digital Imagery
Discrimination
obstructed by
overlaying water
Difficulty with discrimination
due to wave action particularly
from low level photographs
Difficulty with discrimination,
but can apply radiative transfer
correction
Tendency for
confusion
between bottom
types
Improved bottom type
discrimination with input from
an informed operator
Improved bottom type
discrimination with algorithms
and in situ data
Geomorphological
Separability
Provides more accuracy for fine
descriptive resolution
Provides detailed and broad zonal
information
Wavelength data
These data are lost following
digitizing
Wavelength data are retained and
can be used to extrapolate
biological or physical information
3-D perspective
A 3-D portrait is formed
following the overlay of stereo
pairs
Can be achieved by overlaying
imagery on a bathymetric image.
Familiarity with
the aquatic system
Need for remote sensing
operator to be familiar with the
spatial patterns within the
aquatic system
Need for the remote sensing
operator to be familiar not only
with spatial patterns but also with
biological processes that may be
revealed within wavelength data
Availability and
costs
High availability and costs
when coverage is required for
large areas
Requires scheduled satellite
Passover with minimum purchase
order leading to high costs
256
Newman, LeDrew and Lim
and while focusing on the advancements in remote sensing technologies over the past
10 years. Challenges presented by the sensors are described at the end of this section.
3.1 AERIAL PHOTOGRAPHY VERSUS DIGITAL IMAGERY
Aerial photography lags behind digital imagery in several areas, especially in
multi-variable image extraction capabilities, but its comparatively lower cost and
simple technology are particularly attractive when mapping reef environments in
developing countries (Table 3). Aerial photography has been successful in mapping
structural loss (Lewis, 2002), reef extent (Thamrongnawasawat and Hopley, 1994), and
benthic communities (Cuevas-Jimenez and Ardisson, 2002). It has also been used as a
tool for proactive management (Riegl and Piller, 2000). Generally, an aerial
photograph is considered successful at mapping when (1) the spatial resolution of the
map or image conforms to the complexity of the environment so that details of most
interest are revealed; (2) the film is sensitive to wavelengths that penetrate the
overlying water and illuminate the architecturally complex bottom structure; and (3) the
final product is reliable (Chauvaud et al., 1998). With the overwhelming volume of
archived, available aerial photography, there is a trend towards integrating digitized
aerial photographs with digital imagery to improve the delineation of features and, thus,
image accuracy (Green et al., 2000).
Table 3. Comparison between aerial photography and digital imagery of shallow-water coral
reef areas. (Compiled from Chauvaud et al., 1998, Mumby et al., 1997, and Sheppard et al.,
1995)
Issues
Aerial Photography
Digital Imagery
Discrimination
obstructed by
overlaying water
Difficulty with discrimination
due to wave action particularly
from low level photographs
Difficulty with discrimination,
but can apply radiative transfer
correction
Tendency for
confusion
between bottom
types
Improved bottom type
discrimination with input from
an informed operator
Improved bottom type
discrimination with algorithms
and in situ data
Geomorphological
Separability
Provides more accuracy for fine
descriptive resolution
Provides detailed and broad zonal
information
Wavelength data
These data are lost following
digitizing
Wavelength data are retained and
can be used to extrapolate
biological or physical information
3-D perspective
A 3-D portrait is formed
following the overlay of stereo
pairs
Can be achieved by overlaying
imagery on a bathymetric image.
Familiarity with
the aquatic system
Need for remote sensing
operator to be familiar with the
spatial patterns within the
aquatic system
Need for the remote sensing
operator to be familiar not only
with spatial patterns but also with
biological processes that may be
revealed within wavelength data
Availability and
costs
High availability and costs
when coverage is required for
large areas
Requires scheduled satellite
Passover with minimum purchase
order leading to high costs
256
Newman, LeDrew and Lim