134
M. Vespe et al.
(Fortuny-Guash, 2003) based on Cloude and Pottier developed polarimetric decomposition (Cloude and Pottier, 1997). Nunziata et al (2008) propose the use of the
Co-polarised Phase Difference (CPD) between HH and VV returns to discriminate
biogenic from mineral oil because of the relevant different damping properties.
ScanSAR modes have been predominantly selected for oil spill detection because
of the large covered swath and less stringent spatial resolution requirements.
Nevertheless, there are issues related to residual scalloping and elevation beam
boundary that often reduce the data “usability” for this application. Novel products
shall be operationally available for this purpose. In particular, the TopSAR radar
mode (Zan et al., 2006) has been recently implemented by TerraSAR-X by azimuth
beam steering within the different sub-swaths. Differently from ScanSAR, TopSAR
allows a wide swath coverage with nearly uniform signal to noise ratio, therefore
reducing scalloping and range dependent radiometric errors (Meta et al., 2007).
8.3 From Research to Operational Services
In this section, a number of aspects related to operational oil spill detection are presented. The main parameters to be taken into account, when designing operational
SAR based oil spill detection, are the following:
• Minimum detectable dark feature contrast under variable wind speed conditions
(which primarily translates to radiometric resolution but is influenced by noise
level, incidence angle, polarisation, ENL);
• Instantaneous swath (large swath is usually preferred for global routine
monitoring);
• Ability to describe geometric properties of the detected dark patch (shape
structure and area features);
• Ability to estimate the age of the spill (as derived from the shape);
• Revisit frequency (no repeat-pass interferometry over the sea, so not necessarily
with the same beam);
• Tasking lead time (i.e., how fast can an acquisition be planned);
• Delay in delivering the results (detected spills positions at the end user after
overpass);
• Ability to acquire imagery at any time of the day (and not just e.g. at dawn or
dusk passes, because some activities at sea do not occur at those hours);
• Availability (related to scheduling conflicts) and accessibility (how easy is for the
End User to task satellites);
• Reliability (primarily in the sense of reliability of detection, i.e. detection
probability and false alarm rate).
Most of the above mentioned aspects are strictly related to the specific SAR
instrument performance and cannot be varied from an application point of view.
Nevertheless, the “reliability” of the oil spill detection service can be improved
M. Vespe et al.
(Fortuny-Guash, 2003) based on Cloude and Pottier developed polarimetric decomposition (Cloude and Pottier, 1997). Nunziata et al (2008) propose the use of the
Co-polarised Phase Difference (CPD) between HH and VV returns to discriminate
biogenic from mineral oil because of the relevant different damping properties.
ScanSAR modes have been predominantly selected for oil spill detection because
of the large covered swath and less stringent spatial resolution requirements.
Nevertheless, there are issues related to residual scalloping and elevation beam
boundary that often reduce the data “usability” for this application. Novel products
shall be operationally available for this purpose. In particular, the TopSAR radar
mode (Zan et al., 2006) has been recently implemented by TerraSAR-X by azimuth
beam steering within the different sub-swaths. Differently from ScanSAR, TopSAR
allows a wide swath coverage with nearly uniform signal to noise ratio, therefore
reducing scalloping and range dependent radiometric errors (Meta et al., 2007).
8.3 From Research to Operational Services
In this section, a number of aspects related to operational oil spill detection are presented. The main parameters to be taken into account, when designing operational
SAR based oil spill detection, are the following:
• Minimum detectable dark feature contrast under variable wind speed conditions
(which primarily translates to radiometric resolution but is influenced by noise
level, incidence angle, polarisation, ENL);
• Instantaneous swath (large swath is usually preferred for global routine
monitoring);
• Ability to describe geometric properties of the detected dark patch (shape
structure and area features);
• Ability to estimate the age of the spill (as derived from the shape);
• Revisit frequency (no repeat-pass interferometry over the sea, so not necessarily
with the same beam);
• Tasking lead time (i.e., how fast can an acquisition be planned);
• Delay in delivering the results (detected spills positions at the end user after
overpass);
• Ability to acquire imagery at any time of the day (and not just e.g. at dawn or
dusk passes, because some activities at sea do not occur at those hours);
• Availability (related to scheduling conflicts) and accessibility (how easy is for the
End User to task satellites);
• Reliability (primarily in the sense of reliability of detection, i.e. detection
probability and false alarm rate).
Most of the above mentioned aspects are strictly related to the specific SAR
instrument performance and cannot be varied from an application point of view.
Nevertheless, the “reliability” of the oil spill detection service can be improved