Marine Surveillance with RADARSAT2 Ship and Oil Slick

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

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 2011. The overall objective was to investigate the use of dualpolarized and quad-polarized SAR data for maritime surveillance, initially in preparation for RADARSAT-2 using ENVISAT and SIR-C data and then followon 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: – – n The objectives of the oil slick detection study were to: – – © MDA 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 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

Ship Detection Study Site n n Study site was the Strait of Georgia, BC Access to ship-tracking information from Canada Coast Guard shore-based radars 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 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 Vancouver Island © MDA

Ship Validation Data n n Vessel tracked from the Maritime Communications and Traffic Services Centre operated by the Canadian Coast Guard (CCG) The CCG data provided: – – n © MDA continuous tracking ship name, Lloyd’s registry, type, length, speed, direction, etc. 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

Dual-Polarized Data n © MDA 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.

HH n HV © MDA 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.

Wide 1 + Wide 2 Results (HH + HV) 19. 1 - 39. 4 HV TCR: ~ constant with incidence angle HH TCR: increases with increasing incidence angle n n © MDA TCR near range: HV > HH TCR far range: HH > HV At ~ 30 incidence angle, HV and HH TCR are similar Results based on the BC Ferries with lengths between 80 m and 160 m, with the same ships in Wide 1 and Wide 2

Wide 1 + Wide 3 Results (VV+VH) 19. 1 - 31. 1 and 38. 7 - 45. 3 n n n © MDA Seven ships between 26 m and 133 m were detected in Wide 1 and Wide 3 TCR near range: HV > HH TCR far range: HH > HV

Ship Orientation and TCR >125 m n n n CCG data provides accurate heading/course information on each vessel All of the vessels +/- 45° from parallel were put in the parallel category, while the remaining were classed as orthogonal Ships greater > 50 m in length were selected and the TCR estimated for ships that were “parallel” and “perpendicular” to the radar look-direction <50 m 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 © MDA Cantarell oil seep (left) and a subscene of a RADARSAT-2 Scan. SAR Narrow image (right) acquired March 5, 2011 showing the Cantarell oil seep. The inset shows an overlay of the FQW 15 acquired March 1, 2011. RADARSAT-2 quad-polarized Fine and Standard Wide swath data (50 km az x 25 km rg) were acquired.

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

n n © MDA Entropy divergence correlates with co-polarized divergence 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 RADARSAT-2 data were acquired at larger incidence angles Sigma-0 divergence for oil-ocean with increasing incidence angle for co-polarized, but invariant for crosspolarized data

Entropy n n n © MDA Entropy for FQW 2 (top) and FQW 15 (bottom) The incidence angle range for FQW 2 is 19. 1 - 22. 7 and 34. 4 – 36. 0 for FQW 15 The scale on the right is from 0 to 1, with low entropy (blue) and high entropy (red)

Noise Floor and Target Decomposition FQW 15 HH+HV+VV n n n © MDA Cross-polarized return for oil and ocean and the FQW 15 and SQW 15 noise floor The cross-pol (HV) for oil and ocean is at or below the noise floor For low return targets, the use the cross-polarized data may be noise-limited and impact results for target decomposition

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

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

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

Application of the Touzi Decomposition 22. 7 19. 1 36. 0 34. 4 n Dominant eigenvalue ( 1) – 1 n Scattering type phase ( S) – S FQW 2 © MDA FQW 15 s Limited oil-ocean discrimination at small incidence angles (FQW 2), but better at larger incidence angle (FQW 15) good discrimination between oil and ocean for both images, thus suggesting incidenceangle invariance.

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