sensing from satellites, aircraft and shore platforms is a rapidly developing field
that has the capacity to carry out monitoring observations on scales from reef
lagoons to regional and global oceans.
13.1 Introduction
A wide range of frequencies are available in the electromagnetic spectrum for use
in remote sensing of coral reefs (Fig. 11.2), which, in addition to the other remote
sensing disciplines discussed in this book, include the capability at radar wavelengths for measuring a rich set of sea surface characteristics. The discovery of
resonant peaks within radar scatter from the ocean was made by Crombie (1955)
by investigating sea clutter echoes using an ionospheric sounder. However, only
theoretical development of the concept of High Frequency (HF; 3–30 MHz) ocean
radar occurred over the next 15 years, and practical progress was deferred until the
mid-1970s when mini-computers could be taken into the field. For over a decade,
work predominantly involved only discovery research and development, until the
mid 1990s when commercial systems emerged and the focus shifted to applications using radar as an operational tool for measuring coastal currents. HF ocean
radars are now being used to provide current and wave fields around coral reefs
with specific applications related to: connectivity between reefs and other ecosystems; pollution management; and assessing physical stresses leading to coral
bleaching.
Satellite/space-based radar technology followed a similar trajectory in the same
era, where initial development was reliant upon the advent of reliable digital
processing. NASA’s Seasat satellite, launched in 1978, carried the first Synthetic
Aperture Radar (SAR) and scatterometer instruments into space following a
lengthy development period using aircraft. Initially, SAR data were processed
optically; however, some digitally processed Seasat SAR data became available
within a year after launch. Unfortunately, the Seasat satellite experienced a fatal
power system failure, limiting its operating life to just over 100 days. This premature mission termination proved to be a major setback in satellite SAR availability for many years. NASA’s SAR efforts for the next two decades shifted to the
Shuttle Imaging Radar program, concentrating on a number of short-duration
Shuttle missions, culminating with the Shuttle Radar Topography Mission
(SRTM) in 2000. After Seasat, another free-flying satellite SAR was not available
until the European Space Agency (ESA) launched the ERS-1 satellite in 1991. By
that time, digital SAR processing systems were sufficiently developed to enable
near real-time SAR image formation, whereupon ocean, land, cryospheric, and
atmospheric SAR applications began developing rapidly.
This chapter begins with a description of HF radar technology, illustrating some
applications in coral reef management, followed by the natural extension into the
Very High Frequency (VHF; 30–300 MHz) high-resolution system for mapping
342
M. L. Heron et al.
that has the capacity to carry out monitoring observations on scales from reef
lagoons to regional and global oceans.
13.1 Introduction
A wide range of frequencies are available in the electromagnetic spectrum for use
in remote sensing of coral reefs (Fig. 11.2), which, in addition to the other remote
sensing disciplines discussed in this book, include the capability at radar wavelengths for measuring a rich set of sea surface characteristics. The discovery of
resonant peaks within radar scatter from the ocean was made by Crombie (1955)
by investigating sea clutter echoes using an ionospheric sounder. However, only
theoretical development of the concept of High Frequency (HF; 3–30 MHz) ocean
radar occurred over the next 15 years, and practical progress was deferred until the
mid-1970s when mini-computers could be taken into the field. For over a decade,
work predominantly involved only discovery research and development, until the
mid 1990s when commercial systems emerged and the focus shifted to applications using radar as an operational tool for measuring coastal currents. HF ocean
radars are now being used to provide current and wave fields around coral reefs
with specific applications related to: connectivity between reefs and other ecosystems; pollution management; and assessing physical stresses leading to coral
bleaching.
Satellite/space-based radar technology followed a similar trajectory in the same
era, where initial development was reliant upon the advent of reliable digital
processing. NASA’s Seasat satellite, launched in 1978, carried the first Synthetic
Aperture Radar (SAR) and scatterometer instruments into space following a
lengthy development period using aircraft. Initially, SAR data were processed
optically; however, some digitally processed Seasat SAR data became available
within a year after launch. Unfortunately, the Seasat satellite experienced a fatal
power system failure, limiting its operating life to just over 100 days. This premature mission termination proved to be a major setback in satellite SAR availability for many years. NASA’s SAR efforts for the next two decades shifted to the
Shuttle Imaging Radar program, concentrating on a number of short-duration
Shuttle missions, culminating with the Shuttle Radar Topography Mission
(SRTM) in 2000. After Seasat, another free-flying satellite SAR was not available
until the European Space Agency (ESA) launched the ERS-1 satellite in 1991. By
that time, digital SAR processing systems were sufficiently developed to enable
near real-time SAR image formation, whereupon ocean, land, cryospheric, and
atmospheric SAR applications began developing rapidly.
This chapter begins with a description of HF radar technology, illustrating some
applications in coral reef management, followed by the natural extension into the
Very High Frequency (VHF; 30–300 MHz) high-resolution system for mapping
342
M. L. Heron et al.