Session Summaries and Recommendations
Algorithms, Validation and Assimilation
Summary & RECOMMENDATIONS
(by Vincent Kerbaol & Susanne
Improvement of the ENVISAT ASAR
level-2 wave mode product as part of the reprocessing campaign:
Detrending, MTF at low wave-numbers,
ambiguity removal, cut-off estimation
Improvement in the geophysical quality
Empirical approach tuned against NWP
Global statistics of conventional
Requires additional “ training data”
for tuning the algorithm.
Measurement of global map of
individual wave parameters from 3 weeks of ERS-2 wave mode data performed at
DLR and validation campaign initiated.
Cross-spectra algorithm is
particularly well suited for WSS products and first results have been
Wave algorithms exhibit limitations
for high to extreme wind conditions.
Very limited in-situ data sets on the
behaviour of the normalised RCS at high winds (suitability of CMOD models
questionable and would require further tuning to high wind speeds sea states).
Use of historic ERS wave mode archive
for climatologic analysis has been suggested and reprocessing of 2-years
archive to imagettes has been completed at DLR. Global maps of wind speed and
conventional sea state parameters generated
Improvement in the geophysical data quality
after the wave mode Level-2 algorithm improvement (reprocessing of ASAR WV mode
data since December 2002 started at Ifremer):
Decreasing of the rejection rate for
Comparisons w.r.t. models/buoys show:
Overall agreement in the SWH
Larger variations on the shape of the
Use of Wave mode products at different
wave forecast centres
ENVISAT ASAR Level-2 products ASA_WVW_2P
ERS-2 SAR spectrum at ECMWF (until 1st
ENVISAT ASAR Level 1 ASA_WVS_1P (from
1st February 2006 at ECMWF)
Qualitative indicators are crucial and
shall be provided in the products:
SNR, Normalized Variance Wind Speed
Impact of the level-2 wave products in
10% correction after reprocessing with
the upgraded algorithm (compared with independent data)
Increase sampling along the satellite
track (to be considered for future missions)
Increase size of Wave mode imagettes to
improve the wind analysis (to be considered for future missions)
Plan acquisitions at higher incidence angles in VV and HH polarizations
(during limited test periods to gather suitable test data for incidence angles
other than IS2 angles)
Summary & RECOMMENDATIONS
(by Johnny A. Johannessen & Fabrice Collard)
of SAR data by offshore industry (GM and Wide swath mode) for current front and
eddies tracking have been demonstrated based on purely visual interpretation of
sea surface roughness (combined with other source (IR/visible/altimetry), in
particular in area where cloud are frequents and ocean model not accurate
Internal wave are
monitored in various ocean region maybe and there is an opportunity to built a
global database (time of observation, IW crest geocoded poly-lines)
is the base of any future inversion algorithm: promising development have been
recently made to model effect of radar cross section and Doppler velocities
modulation by variable surface currents.
analysis techniques based on wavelet techniques have been investigated for
feature extraction and tracking. This analysis benefits from use of sequential
SAR acquisitions a few hours apart from different SAR platforms.
of surface current estimation from Doppler centroid anomaly can be routinely
estimated but requires a posteriori knowledge of satellite attitude at the
precision of a few milli-degrees. A validation campaign would be required to
estimate the errors associated to this measurement.
Develop feature extraction algorithms
based on dual polarisation (even in wide swath mode).
Have a background mission monitoring (GM
and wide swath mode) in strong currents/eddies area (from shore to continental
Increase the temporal repeat time (at
least one image every day). May be achieved by constellations like
Cosmo-Skymed. Continuity on long term (mission not finished before algorithms
are finally developed and validated).
Provide restituted attitude information to users as a regular product
(such as restituted orbit product).
OCEAN WIND APPLICATIONS
Summary & RECOMMENDATIONS
(by J. Horstmann & E. Attema
Answers to Seed Questions
What are the major methodologies and which of these can be used on a fully
Wind directions from
wind streaks via:
Local Gradient Method
Major differences besides the techniques are the utilized scales
Wind Speeds from the
normalized radar cross section via:
C-Band models, for HH the polarization ratio has to be taken into
Thompson et al., 1998 (q) tuning via a (between 0.4 and 1.2)
Elfouhaily, 1998 (q)
Mouche et al., 2004 (q, F)
Engen et al., 2004 (q, F,u10)
Are there new promising methodologies?
using incidence angle dependence of the NRCS
Combination of different approaches
What are the resolutions, accuracies and limitations of the available
Resolution of approximately 10 km with an error of typically 20 deg
decreasing with wind speed. Dependent on the presence of streaks
Resolution of ~ 500 m (depending on SAR resolution and number of looks).
Wind speed error is typically 1.6 m/s for wind speeds below 20 m/s.
Where are the most useful applications of SAR wind field retrieval and what are
Tuning of high resolution wind models
Energy assessment in offshore wind farming
Investigation of turbulence (scientific)
Hurricanes (forecast, scientific) data are required near real time
Winds play an
important role in most other SAR ocean applications, e.g. slick detection and
What are the needs for accurate SAR wind retrieval (calibration, modes,
calibration < 0.5 dB
preferable at incidence angles > 25deg
Better knowledge of
the polarization ratio
Perform a detailed
investigation of the polarization ratio
Analyze what is
the accuracy and where are the limitations of the CMOD5 model at winds above 20
fetch dependencies as well as the presence of swell on wind speed retrieval.
Investigation of the
error introduced by using the C-band models for very high resolution.
Acquisition of ASAR wave mode data at different
polarizations and incidence angles.
acquisitions of ASAR data in Hurricane and Typhoon conditions and their
availability in near real time (special BRM is already implemented in the Golf of Mexico & Caribbean Sea in ScanSAR mode)
Session Summary & RECOMMENDATIONS
(by J.C.B. da Silva & F.
1. Accidents in severe weather events using
satellite radar data
Wind and wave fields around offshore
oil platforms (Ekofisk, Draupner and Fino) were retrieved from SAR, analysed
and compared with environmental data collection, laser arrays and WAMOS
directional wave radar
SAR yields measurements over a 100km x
100km area and thus shows the spatial structure of the wave field (e.g. wave
refraction around islands)
Direction of the wind measurements and
the high frequency wave components of the laser array fit very well
2. Surface wave
spectrum in the Gulf of Tehuantepec
Detailed analysis of SAR images
provides information of spatial variability of wave spectra, also observed from
direct measurements with wave staff array revealing the variable nature of
Influence of swell on the momentum
flux between ocean and atmosphere is determined directly and an enhancement of
the drag coefficient is also observed
3. A global
quality-controlled spectral wave database
Integration of observations and models
are essential to get quality controlled consistent basic databases to build
retrieval of 2-D ocean wave spectra (PARSA)
A parametric inversion scheme for SAR retrieval of 2-D ocean
wave spectra from look cross spectra was presented
The PArtition Rescaling and Shift Algorithm (PARSA) provides
estimates of complete 2-D ocean wave spectra using prior information, making
use of the complex information provided by cross spectra
Validations based on triple collocations with buoys (WAM,
NDBC buoy and PARSA), indicates PARSA improves spectrum when compared to WAM
5. SAR Wave
Mode Imagette under extreme wind and wave
Good coverage during hurricanes and typhoons offering the
opportunity of a statistical study of storms dynamics, in the four
quadrants. The main objective of project is to make a synergistic use of
Spectral information provided by SAR contains valuable
information about the ocean wave dynamics in storms
Internal Waves from Luzon Strait
Non-linear IWs in the South China Sea propagate westward of
Luzon Strait, with typical phase velocities of Cp=3m/s (fastest reported so
far). In situ measurements support velocities retrieved from sensor synergy
Envisat Wide Swath mode is necessary to study the generation
and propagation characteristics of such large-scale internal waves
Answers to Seed Questions AND
What special SAR
signatures characterize very fast propagating internal waves in deep ocean?
What are the most useful SAR imaging modes to identify internal wave generation
sites, and internal wave generation mechanisms? Could future satellite missions
with Along Track Interferometric capabilities be used to measure surface
currents associated to internal waves and tides? Have we improved our capabilities
to distinguish atmospheric and oceanic internal waves observed by SAR?
Wide Swath mode is essential to study
generation and propagation of internal waves, although narrow swath is also
very important for finer scale observations. Along-track Interferometry should
be used in future to retrieve current fields associated with internal waves and
tides. Oceanic and atmospheric origin of internal waves is still a possible
cause of misinterpretation. Methods to distinguish those signatures need
further development. The ability to get further environment information (other
physical variables) through remote sensing, as well as including multi
polarization modes, would lead us to a better position to make the distinction
What new SAR
products can be developed for coastal engineering studies? Can we develop
current algorithms to be applied to the near-shore and the surf zone (include
wave breaking processes)? Should this be addressed in future spaceborne SAR
SAR images with better than 5m resolution
are required. Special attention to depth dependence of inversion schemes should
be given, where wave dispersion relation and SAR imaging theory with general
validity should be taken into account.
Is it possible to
use methods developed to detect extreme wave events for an early warning
system, based on SAR observations (faster delivery of real time data)?
Extreme internal wave events are still a
main concern for offshore operations. It is important to further study the
generation mechanisms in order to be able to predict time and space variability
Is there any theoretical work to support
scatterometer signal response as a function of wind speed for ocean surface in
the presence of swell?
Presence of swell and also fetch dependency
on scatterometry. Polarimetric measurements would provide further information
on sea state characteristics and roughness influencing backscatter
How can we make
use of SAR to improve our ability
to predict the transformation of offshore spectra (from wave forecasting models)
into inshore regions with sensitive engineering and navigational needs?
Main source of error is probably the
bathymetry information. Finer
resolution for SAR images are required to determine the wave spectrum
nearshore. In order to provide useful information for operational purposes
(engineering, navigation, rescue, etc) real time delivery of SAR images is
Can we identify
special test-sites for validation of wave products where characteristic
conditions exist and in situ measurements are being conducted?
For calibration and validation purposes a multinational experiment
should be conducted. Even if one of the main driving
force could be target detection, most environmental variables should be
retrieved, wind, waves, currents, etc. Since there are no new planed missions
with scatterometer, SAR images should be considered for wind field retrieval.
Participation of major space agencies is recommended
Discuss the use of
the historic ERS wave mode data set
Wave mode re-analysis to integrate the various missions is required
What is the
climate requirement for 2-d sea-state measurements from SAR? (e.g. directional wave height variance spectrum over what
Long term statistics of wave conditions has
been reported with possible association to global change. Uniform processing providing
cross spectra from imagettes would assist in building a long term data base.
Applications (insurance for instance) require wave statistics over longer
periods than ten years
OIL SPILL AND
Session Summary & RECOMMENDATIONS
(by J.A. Lorenzzetti, J.
Schultz-Stellenfleth, W. Alpers)
The session was held on January 25, 2006 from 09:00 to 16:00. A total of 16
papers were orally presented. The paper’s authors included 9 European countries,
United States, Mexico and Brazil.
In a broad sense, the presented papers can be categorized into three groups: a)
mathematical models of data analysis (5); b) operational experiences of oil
spill and ship detection (7); c) commercial use of SAR data for the monitoring
of oil seeps (1), and d) science oriented applications of SAR data (2).
At the end of the oral presentations, a discussion plenary session was held,
which was guided by a set of pre-defined list of seed questions.
The following main points can be highlighted from the oral presentations and
It is not possible to define a specific set of SAR system that would meet all
the requirements of OSSD. In particular, for ship detection, from a polarimetric
SAR, HH pol is the best option, with the HV pol channel being a good choice for
targets at steep incidence angles.
Synergistic use of different SAR images together with other satellite systems
(visible, infrared, scatterometer, altimeter) and in situ data are highly
recommended for OSSD.
For ship detection, a case has been made that a Wide Swath, even at the cost of
lower resolution would be preferred for the open ocean, which normally present
larger ships, however, still a resolution better than 30m would be desirable;
present ASAR-WS is not good enough. For the coastal zone ship detection
applications, Narrow Swath with high resolution seems to be the best option.
A set of advanced techniques of data analysis of SAR image processing for OSSD
were presented. All of them seem to present good potential, but in general,
they still lack an adequate validation. It is here suggested that ESA should support a
benchmarking project in which all different groups which are doing research in
this area would process the same set of SAR images with the support of the same
ancillary environmental data, such as done in the DECLIMS project.
Regarding the Envisat data availability for operational use, at least for
outside the KSAT antenna footprint, still the current delays are not adequate. Better than 30-60 minutes is
essential. It has been reported that delays of more than 24 h are not
uncommon. The heavy load of ESA countries data requests were reported to be a
major constraint in supporting operational users of ASAR data.
The important problem of a clear discrimination between real oil spills (or oil
seeps) from look-alike features, is still not resolved. Although several
methods of automatic detection of oil spills have been presented, there still a
need for a trained operator for final verification.
For an operational maritime surveillance system, persistence of coverage seems
to be a bottleneck that cannot be resolved with a single satellite SAR system.
A constellation of satellites seems to be the only solution to shorten the
revisit time. Some applications demand a monitoring scale as short as few
hours, or even less. The new SAR systems that were very recently launched and
those which are planed to fly in the next few years from countries like Germany,
Italy, Canada, China and India, for example, could guarantee the persistence
and continuity of data availability for the coming years. An alternative for
decreasing periods without SAR data is the synergy with airborne sensors and
coastal systems like CODAR. When SAR is used in conjunction with other vessel
systems like VMS (Vessel Monitoring System-mandatory for fishing vessels larger
than 12 m) and AIS (Automatic Identification of Ships – mandatory after 2008),
requirements on revisit periods for ship detection should be less strict.
Meantime, surveillance should benefit from more flexible and faster tasking
possibilities (e.g. quick scheduling of SAR data acquisition due to emergency
Besides the important role in marine pollution monitoring, the use of SAR data
for oil slick monitoring must be viewed as another component methodology for
climate studies considering the strong impact of such films have in decreasing
the rates of gas exchange between the oceans and the atmosphere.
Session Summary & RECOMMENDATIONS
(by H. Johnsen & W.
Spaceborne SAR Systems can be used to produce high
quality bathymetric maps in coastal waters with topography up to 30 m depth.
This capability can be used to improve the navigation safety along the coast as
well as to study the modifications of the coastal current regimes (i.e. due to
the building of harbours).
Marine surface films, often present in
coastal areas, may be related to the presence of hydrodynamic processes i.e.
plumes, internal waves, eddies. The slick visibility is greatly dependent by
the electromagnetic wavelength. Therefore the combined use of satellite images
acquired at microwave, visible and IR frequencies can improve the
discrimination capabilities between slicks and other oceanic and atmospheric
phenomena. In this context the effort is to investigate on the physical
mechanisms which are related to the slick signatures using auxiliary
information provided by a multi-sensor approach.
(by P. Clemente-Colón &
Ben Holt )
Answers to Seed Questions AND
Are there any pressing science issues that need
to be explored?
- Ice thickness is a
critical parameter not easily assessed from satellite SAR data. Based upon comparisons
with EM thickness measurements, there is an apparent increase in backscatter
with increasing thickness beyond 2m with HH at least for first year ice. However,
a related study in the Baltic had an unclear relationship. There is little
sensitivity of HV to increasing thickness. Additional investigations are required including over
- Further work on sea ice
characterization using polarimetric and multi-polarization data should be
undertaken to improve sea ice type mapping.
there any new algorithms or techniques that that should be considered?
- From operational
side a better handle on how to determine ice concentration through improvements
in SAR automated and semi-automated objective techniques using
multi-pol/polarimetric is needed
-In some Centers, the
lack of automated processing may impose a limitation on the use of SAR data.
-There is a need for better
L-band and fully polarimetric characterization of sea ice and how this can be
used together with C-band dual pol and polarimetric mode including
-Deriving new and
young ice sea ice thickness estimates from wave-ice interaction has been
there any recommendations to modify or enhance the Envisat mission over the
polar or sea ice covered regions, the ALOS mission?
- Enhancements on sea
ice characterization using multi-band data should be further investigated.
- Can the daily ASAR coverage be
improved over the polar regions?
This would improve derived ice motion fields.
- Particularly, increased access
to ASAR Wide Swath acquisitions around Antarctica should be made available to
improve the quality of NIC sea ice charts (type/stage of development) and
provide estimates of sea ice thickness for PolarView and all other users.
- The limitations of using GMM for
ice charting should be explored.
- The sea ice
community should recommend to JAXA that sea ice coverage be added to the basic
observation plan, which is presently primarily over land.
polarization with cross-pol improves discrimination of open water from ice,
smooth and rough ice, especially when used in combination with HH. Cross-pol shows little improvement with
smooth and young ice types.
- L-band data appears
to improve the identification of ridges compared to C-band. The use of Envisat together with ALOS
will improve overall understanding of sea ice mass volume.
there any recommendations that may enhance the exploitation of the Sentinel-1
mission for polar and sea ice applications?
-There is a desire for
a multi-frequency satellite mission similar to the SIR-C/X-SAR experience.
-The need for the use
of a SAR constellation to provide high revisit time over highly dynamic se ice
regions was suggested (e.g. RADARSAT-2 follow-on SAR Constellation Mission
[2011+] plus other missions)