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R. Romeiser et al.
inhomogeneous and variable, as can be expected in the river mouth of this strong
river, which possibly passes a range of different water depths that would trigger
bands of acceleration and deceleration.
5.5 Summary and Conclusions
We have given an overview of the state of the art in the field of high-resolution surface current measurements from space by conventional and interferometric SAR,
including a description of the two existing techniques, a review of experimental
results from ENVISAT ASAR and TerraSAR-X, and a discussion of possible and
desirable further developments and promising applications. While the basic concepts of Doppler anomaly analysis of conventional SAR data and of along-track
interferometry were developed earlier, it was in the last decade that first successful
current measurements from space by both methods could be demonstrated, using
conventional SAR data from ERS and ENVISAT and interferometric SAR data from
SRTM. With the development of robust data processing and correction methods,
the addition of Doppler information to standard ASAR data products from ESA,
and the implementation of experimental ATI capabilities on TerraSAR-X, conventional SAR- and ATI-based current measurements can now be made available for
a variety of applications, and further development in this field will depend on user
demand and financial support rather than on the solution of major technological
problems.
The Doppler centroid anomaly analysis of conventional SAR data works with all
SAR images (including archived ones) and provides maps of line-of-sight currents
with spatial resolutions in the kilometer range within swaths of up to 400–500 km.
The effective spatial resolution of ATI-derived line-of-sight current fields is on the
order of 1 km within a swath of up to 100 km, but it could be improved by about one
order of magnitude with improved system parameters (longer along-track baseline,
reduced instrument noise) on future satellites. Furthermore, a spaceborne dual-beam
along-track InSAR could measure two current components during a single overpass
to obtain fully two-dimensional vector current maps.
So far we have demonstrated the retrieval of coarse-resolution global current
maps from ENVISAT ASAR Wave Mode data and the observation of regional current features, such as the Agulhas Current, with Image Mode and Wide Swath data,
as well as the imaging of current fields in coastal waters and rivers with ATI data
from SRTM and TerraSAR-X. We see a variety of promising applications in the
open ocean, coastal waters, and river estuaries, such as scientific studies on turbulence structures, shallow-water bathymetry monitoring, studies related to coastal
and offshore engineering projects, and river runoff monitoring. Altogether, current
measurements by spaceborne SAR and ATI seem to have the potential to become a
widely used remote sensing technique, with a level of maturity comparable to radar
altimetry, wind scatterometry, and SAR-based oil spill detection or wave spectra
retrievals, within the coming 10 years.
R. Romeiser et al.
inhomogeneous and variable, as can be expected in the river mouth of this strong
river, which possibly passes a range of different water depths that would trigger
bands of acceleration and deceleration.
5.5 Summary and Conclusions
We have given an overview of the state of the art in the field of high-resolution surface current measurements from space by conventional and interferometric SAR,
including a description of the two existing techniques, a review of experimental
results from ENVISAT ASAR and TerraSAR-X, and a discussion of possible and
desirable further developments and promising applications. While the basic concepts of Doppler anomaly analysis of conventional SAR data and of along-track
interferometry were developed earlier, it was in the last decade that first successful
current measurements from space by both methods could be demonstrated, using
conventional SAR data from ERS and ENVISAT and interferometric SAR data from
SRTM. With the development of robust data processing and correction methods,
the addition of Doppler information to standard ASAR data products from ESA,
and the implementation of experimental ATI capabilities on TerraSAR-X, conventional SAR- and ATI-based current measurements can now be made available for
a variety of applications, and further development in this field will depend on user
demand and financial support rather than on the solution of major technological
problems.
The Doppler centroid anomaly analysis of conventional SAR data works with all
SAR images (including archived ones) and provides maps of line-of-sight currents
with spatial resolutions in the kilometer range within swaths of up to 400–500 km.
The effective spatial resolution of ATI-derived line-of-sight current fields is on the
order of 1 km within a swath of up to 100 km, but it could be improved by about one
order of magnitude with improved system parameters (longer along-track baseline,
reduced instrument noise) on future satellites. Furthermore, a spaceborne dual-beam
along-track InSAR could measure two current components during a single overpass
to obtain fully two-dimensional vector current maps.
So far we have demonstrated the retrieval of coarse-resolution global current
maps from ENVISAT ASAR Wave Mode data and the observation of regional current features, such as the Agulhas Current, with Image Mode and Wide Swath data,
as well as the imaging of current fields in coastal waters and rivers with ATI data
from SRTM and TerraSAR-X. We see a variety of promising applications in the
open ocean, coastal waters, and river estuaries, such as scientific studies on turbulence structures, shallow-water bathymetry monitoring, studies related to coastal
and offshore engineering projects, and river runoff monitoring. Altogether, current
measurements by spaceborne SAR and ATI seem to have the potential to become a
widely used remote sensing technique, with a level of maturity comparable to radar
altimetry, wind scatterometry, and SAR-based oil spill detection or wave spectra
retrievals, within the coming 10 years.