Marine Surveillance with RADARSAT-2: Ship and Oil Slick Detection Gordon Staples, Jeff Hurley, Gillian Robert, Karen Bannerman MDA GSI Richmond, BC

© MDA Outline n Project Objectives n Ship Detection n Oil Slick Detection n Conclusions

© MDA Introduction n Canadian Space Agency EOADP-funded project that started in June 2007 and finished in March The overall objective was to investigate the use of dual-polarized and quad-polarized SAR data for maritime surveillance, initially in preparation for RADARSAT-2 using ENVISAT and SIR-C data and then follow- on with RADARSAT-2 data. n The project had two focus areas: ship detection and oil slick detection n The objectives of the ship detection were to: – Assess the use dual-polarized (and quad pol) as a function of incidence angle – Assess detection and ship orientation with-respect-to radar look direction n The objectives of the oil slick detection study were to: – Investigate the use of the polarimetric entropy for oil slick characterization – Understand the application of incoherent target decomposition algorithms using RADARSAT-2 quad-polarized wide-swath modes

© MDA Ship Detection Study Site n Study site was the Strait of Georgia, BC n Access to ship-tracking information from Canada Coast Guard shore-based radars n Ships have predictable routes (e.g. BC Ferries), so it was possible to image the same ship, in the same orientation, but using a different incidence angle n Variable wind speeds, but nothing too extreme – Wind speeds were typically less than 10 m/s Strait of Georgia study site showing ship Routes for ferry traffic between the BC Mainland and Vancouver Island

© MDA n Vessel tracked from the Maritime Communications and Traffic Services Centre operated by the Canadian Coast Guard (CCG) n The CCG data provided: – continuous tracking – ship name, Lloyd’s registry, type, length, speed, direction, etc. n The time difference between the CCG ship data and the RADARSAT-2 acquisition was typically less than a few minutes, so positive identification was possible Ship Validation Data

© MDA Dual-Polarized Data n The data were acquired in ascending mode since previous work with ENVISAT data indicated that in general there was more ship traffic at ~ 6 PM versus ~ 6 AM.

© MDA HH HV n Wide 1 image (HH+HV) acquired August 4 (left) and wide speed derived from the HH image (top). Note the high wind speeds that appear as bright returns in the HH image, but less pronounced in the HV image.

© MDA Wide 1 + Wide 2 Results (HH + HV) 19.1   HV TCR: ~ constant with incidence angle HH TCR: increases with increasing incidence angle n TCR near range: HV > HH n TCR far range: HH > HV n At ~ 30  incidence angle, HV and HH TCR are similar n Results based on the BC Ferries with lengths between 80 m and 160 m, with the same ships in Wide 1 and Wide 2

© MDA Wide 1 + Wide 3 Results (VV+VH) 19.1   and 38.7   n Seven ships between 26 m and 133 m were detected in Wide 1 and Wide 3 n TCR near range: HV > HH n TCR far range: HH > HV

© MDA >125 m <50m Ship Orientation and TCR n CCG data provides accurate heading/course information on each vessel n All of the vessels +/- 45° from parallel were put in the parallel category, while the remaining were classed as orthogonal n Ships greater > 50 m in length were selected and the TCR estimated for ships that were “parallel” and “perpendicular” to the radar look-direction As the ship length decreases, it was difficult to discern orientation (depends on radar resolution – 30 m for this example)

© MDA As ship length increased, there was a trend for the TCR (VV or VH) to be larger when the ship was oriented perpendicular to the radar look direction vs. parallel

© MDA Study Site Cantarell Oil Seep n Cantarell oil seep (left) and a subscene of a RADARSAT-2 ScanSAR Narrow image (right) acquired March 5, 2011 showing the Cantarell oil seep. The inset shows an overlay of the FQW15 acquired March 1, RADARSAT-2 quad-polarized Fine and Standard Wide swath data (50 km az x 25 km rg) were acquired.

© MDA Cantarell slicks The entropy increased with oil viscosity (IFO > Cantarell), but was this increase related to oil properties or incidence angle? Differences in the Cloude-Pottier entropy were observed between oil types: Intermediate Fuel Oil (IFO) and oil from the Cantarell seep SIR-C RADARSAT-2

© MDA n Entropy divergence correlates with co-polarized divergence n Entropy increased with incidence angle, but entropy is derived from the coherency matrix which is derived from the scattering matrix, so the relationship makes sense  oil-type dependency is suspect n RADARSAT-2 data were acquired at larger incidence angles n Sigma-0 divergence for oil-ocean with increasing incidence angle for co-polarized, but invariant for cross- polarized data

© MDA Entropy n Entropy for FQW2 (top) and FQW15 (bottom) n The incidence angle range for FQW2 is 19.1   and 34.4  – 36.0  for FQW15 n The scale on the right is from 0 to 1, with low entropy (blue) and high entropy (red)

© MDA Noise Floor and Target Decomposition n Cross-polarized return for oil and ocean and the FQW15 and SQW15 noise floor n The cross-pol (HV) for oil and ocean is at or below the noise floor n For low return targets, the use the cross-polarized data may be noise-limited and impact results for target decomposition FQW15 HH+HV+VV

© MDA Eigenvalues n Eigenvalues 1 and 2 (top) and 3 (bottom) for oil and ocean calculated from the 3x3 coherency matrix n Ocean scattering: – 1 invariant with incidence angle n Oil scattering: – 1 dominates to about 25  incidence angle, and then 2 increases ( 1 > 2 ) n For both oil and ocean, 3 << ( 1 and 2 ) n 3  0 (HV polarization)

© MDA Target Decomposition 3x3 vs. 2x2 Coherency Matrix n Incoherent target decomposition (e.g. Cloude-Pottier, Touzi) use co-polarized and cross-polarized data derived from (usually) the 3x3 coherency matrix n The dominance of the first and second eigenvalue (at smaller incidence angles) suggests that the cross-polarized terms in the 3x3 coherency matrix can be neglected n To assess the impact of neglecting the cross-polarized terms, the 2x2 symmetric coherency matrix was formed by setting the cross-polarized terms, S HV = 0

© MDA Dominant eigenvalue (left) and Touzi scattering type phase (right) derived from 3x3 coherency matrix (top), 2x2 coherency matrix (middle), and the difference (bottom). The differences are mainly in the offshore platforms. FQW2 data

© MDA Application of the Touzi Decomposition n Dominant eigenvalue ( 1 ) – Limited oil-ocean discrimination at small incidence angles (FQW2), but better at larger incidence angle (FQW15) n Scattering type phase (   S ) – good discrimination between oil and ocean for both images, thus suggesting incidence- angle invariance. 1 SS ss FQW2FQW  19.1  34.4  36.0 

© MDA Summary Ship Detection n TCR is larger for: – small incidence angles for HV – large incidence angles for HH or VV n TCR (orthogonal) > TCR (parallel) as ship length increases from ~ 50 m to ~175 m n The use of co/cros-pol data provides good ship detection across a large range of incidence angles Oil Slick Detection n The entropy increased with incidence angle, so oil-type discrimination requires validation with different oil types n Scattering dominated by 1 and 2 suggesting that 3 can be neglected n Work is in progress to further understand the use of incoherent target decomposition for oil slick discrimination (interslick variability and oil-type differences)