4
c. TSATSOULIS AND R. KWOK
Based on such analyses, sea ice extent and thickness would appear to be sensitive
indicators of climate change, and this has resulted in considerable interest in developing procedures for monitoring the extent and behavior of the sea ice cover. It is the intent
of this book to provide a survey of the procedures currently being developed for remote
sensing of the sea ice cover with synthetic aperture radar.
1.2
Synthetic Aperture Radar Remote Sensing of the Sea Ice Cover
In the early 1970S, the launch of polar orbiting satellites allowed sea ice studies using data
from visible and infrared imagery. However, sea ice data analyses based on visible and
infrared wavelength imagery are limited by cloud cover and the lack of solar illumination during the polar winter. Extensive cloud cover during the summer months obscures
the ice pack a large percentage of the time. These limitations have led to increased reliance
on sensors from the microwave portion of the electromagnetic spectrum.
The first sensor to provide day/night large scale remote sensing of sea ice cover was
the Electronically Scanning Microwave Radiometer (ESMR), which flew from 1973 to
1976. This sensor was replaced by the Scanning Multichannel Microwave Radiometer
(SMMR) which provided an almost continuous record of observations from 1978 to 1987.
Current passive microwave observations are provided by the series of Special Sensor
Microwave Imager (SSM/I) instruments operated by the Defense Meteorological Satellite Program. These passive microwave sensors are of fairly coarse resolution and are
affected by atmospheric water vapor and cloud water content. Analyzed sea ice products of ice concentration and ice types are routinely produced on a 25-km grid.
In 1978, the polar orbiting SEASAT satellite carrying an L-band synthetic aperture
radar (SAR) produced the first high resolution imagery for observation of the Earth's
surface from space. SEASAT imaged a 100-km-wide swath at 25-m resolution. Although
it operated for only 90 days, SEASAT collected a sizable volume of data which contributed to furthering the understanding of SAR and its applications. With its moderate
frequency, the L-band waves penetrated relatively deeply into the older, low salinity ice,
so that volume scattering from the inhomogeneities gave a significant return. This provided a marked contrast between the backscatter of first-year and multi-year sea ice,
allowing investigators an alternate view of the ice cover to that provided by passive
microwave observations. It was also shown that high resolution ice motion could be
observed in successive SAR observations. This SEASAT dataset clearly demonstrated dIe
potential of SAR for both research and operational applications in ice-covered waters.
In 1983, the Soviet Union launched the first KOSMOS-1500 OKEAN satellite with an
X-band side looking radar (SLR, sometimes referred to as real aperture radar, RAR).
Although the resolution was relatively coarse (2.5 km along-track, 1.3 km cross-track),
its 450-km-wide swath provided the first true synoptic scale radar images of the earth.
There have been several OKEAN satellites, with a continuous series of improvements
to the radar complement. Ukraine has taken over responsibility for the OKEAN series,
and the latest satellite offers X-band SLR with two 700-km swaths and spatial resolution of about 1 km at the near range. The Soviet Union launched KOSMOS-1870 carrying a SAR that operated in S-band in 1987. It had a very narrow 30-km-swath and featured 25-m spatial resolution. This instrument evolved into ALMAZ-1, which was
launched in 1991. ALMAZ-1 used the same S-band (10 cm) wavelength, but had an
c. TSATSOULIS AND R. KWOK
Based on such analyses, sea ice extent and thickness would appear to be sensitive
indicators of climate change, and this has resulted in considerable interest in developing procedures for monitoring the extent and behavior of the sea ice cover. It is the intent
of this book to provide a survey of the procedures currently being developed for remote
sensing of the sea ice cover with synthetic aperture radar.
1.2
Synthetic Aperture Radar Remote Sensing of the Sea Ice Cover
In the early 1970S, the launch of polar orbiting satellites allowed sea ice studies using data
from visible and infrared imagery. However, sea ice data analyses based on visible and
infrared wavelength imagery are limited by cloud cover and the lack of solar illumination during the polar winter. Extensive cloud cover during the summer months obscures
the ice pack a large percentage of the time. These limitations have led to increased reliance
on sensors from the microwave portion of the electromagnetic spectrum.
The first sensor to provide day/night large scale remote sensing of sea ice cover was
the Electronically Scanning Microwave Radiometer (ESMR), which flew from 1973 to
1976. This sensor was replaced by the Scanning Multichannel Microwave Radiometer
(SMMR) which provided an almost continuous record of observations from 1978 to 1987.
Current passive microwave observations are provided by the series of Special Sensor
Microwave Imager (SSM/I) instruments operated by the Defense Meteorological Satellite Program. These passive microwave sensors are of fairly coarse resolution and are
affected by atmospheric water vapor and cloud water content. Analyzed sea ice products of ice concentration and ice types are routinely produced on a 25-km grid.
In 1978, the polar orbiting SEASAT satellite carrying an L-band synthetic aperture
radar (SAR) produced the first high resolution imagery for observation of the Earth's
surface from space. SEASAT imaged a 100-km-wide swath at 25-m resolution. Although
it operated for only 90 days, SEASAT collected a sizable volume of data which contributed to furthering the understanding of SAR and its applications. With its moderate
frequency, the L-band waves penetrated relatively deeply into the older, low salinity ice,
so that volume scattering from the inhomogeneities gave a significant return. This provided a marked contrast between the backscatter of first-year and multi-year sea ice,
allowing investigators an alternate view of the ice cover to that provided by passive
microwave observations. It was also shown that high resolution ice motion could be
observed in successive SAR observations. This SEASAT dataset clearly demonstrated dIe
potential of SAR for both research and operational applications in ice-covered waters.
In 1983, the Soviet Union launched the first KOSMOS-1500 OKEAN satellite with an
X-band side looking radar (SLR, sometimes referred to as real aperture radar, RAR).
Although the resolution was relatively coarse (2.5 km along-track, 1.3 km cross-track),
its 450-km-wide swath provided the first true synoptic scale radar images of the earth.
There have been several OKEAN satellites, with a continuous series of improvements
to the radar complement. Ukraine has taken over responsibility for the OKEAN series,
and the latest satellite offers X-band SLR with two 700-km swaths and spatial resolution of about 1 km at the near range. The Soviet Union launched KOSMOS-1870 carrying a SAR that operated in S-band in 1987. It had a very narrow 30-km-swath and featured 25-m spatial resolution. This instrument evolved into ALMAZ-1, which was
launched in 1991. ALMAZ-1 used the same S-band (10 cm) wavelength, but had an