Ship detection signatures in AP mode data

Paper number

IAC-05-B1.P.06

Author

Ms. Tonje Nanette Arnesen, Norwegian Defence Research Establishment, Norway

Year

2005

Abstract

Canada and Norway are two countries that have used spaceborne Synthetic Aperture Radar (SAR) operationally due to large economic and fisheries zones. RADARSAT-1 and ENVISAT have been used in addition to coast guard helicopters, aircrafts, and boats to monitor vast areas. Satellites have the advantage of giving good coverage. An important factor for being able to detect ships is the imaging geometry. Former radar satellites were constructed in a way where the radar reflectivity from the sea surface and the ship are approximately equally strong, which result in poorer contrast between ship and sea. ENVISAT’s Advanced Synthetic Aperture Radar (ASAR) is on the other hand based on newer technology, and is more advanced. The Alternating Polarization (AP) mode gives simultaneously measurements of reflections from ship and sea with different polarizations of the radar signal.

The paper presents a study, which is a part of an ENVISAT-AO project and the Norwegian SATHAV program. SATHAV is an ongoing national maritime program to utilize Earth observation data from satellite, and is established after an initiative from the Norwegian Space Centre. The study is performed in cooperation with Kongsberg Satellite Services AS and the Norwegian Defence Research Establishment. It is a preparation for the Canadian dual-polarized ScanSAR RADARSAT-2 satellite, which will also have the possibility of full-polarization imaging of one scene.  

The capacity of ENVISATs ASAR instrument is evaluated. The polarization ratios (VV/VH, HH/HV, and VV/HH) and the influence of geometry on the radar backscatter signal of a moored production ship (Norne FPSO - Floating Processing Storage Offloading) in the Norne field outside the west coast of Norway are examined. The Norne field is of special interest because it is possible to systematically collect data over the same ship with different ASAR subswaths and polarizations to be able to estimate which combinations of these parameters and sea conditions give the best TCR. 

The reflection from the ocean surface is very low using VH- or HV-polarization. The possibility to detect ships depends on if the ship is above the noise floor. The ship detection capability improves using cross-polarization for small incidence angles. The results for large incidence angles using cross-polarization are surprising. The improvement is quantified for cross-polarization vs. co-polarization, and recommendations for different subswaths, incidence angles, and polarizations for maximum coverage and detection rates are given. 

The paper also presents an investigation of the minimum detectable vessel length in ENVISAT AP mode images. Nine images have been ordered over the Oslofjord in Norway, and analysed to investigate the minimum detectable vessel length in cross-polarized data. 

Abstract document

IAC-05-B1.P.06.pdf

Manuscript document

IAC-05-B1.P.06.pdf (🔒 authorized access only).

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