SAR can obtain high-resolution images of targets in all types of weather

all day

and at long distance.It has significant value to civil and military fields.Harbor detection is also an important aspect for remote sensing ocean application research.Monitoring ocean targets using SAR images is also an important research direction.A long coastline has several small harbors

which consist of many docks and jetties.Large harbors are monitored all the time.By contrast

small harbors with less importance are neglected.However

these small harbors

where ships temporarily park

may have certain important targets at critical times.Thus

small harbors should also be automatically detected from large-scene SAR images.This study aims to detect small harbors in large-scene SAR images efficiently.Detection methods are complex because the coastline is always flexible.The shape of small harbors is irregular

and detectors can be easily deceived by the changing coastline.Moreover

a large scene may consist of many false small harbors.Thus

detection may result in high false alarm rate and low accuracy

thereby making it unusable. The small harbors have geometrical and radiation characteristics.The geometrical characteristics refer to the natural and artificial shape of small harbors；thus

the shape of small harbors varies.The radiation characteristics refer to the complexity of the SAR image of the harbors compared with optical images due to the interference of the speckle and other strong scatter.An extraction method for small harbor areas in large-scene SAR images is proposed in this study based on small harbor characteristics.The method is divided into three stages.First

a multiscale corner detector is adopted to extract potential areas.In different scales of a coastline

a corner represents varied information.An original scale image can extract several corners

some of which are small ships and docks

whereas some are speckled noise.These corners will disappear when the image is downsampled

and only the entire harbor corner can be observed.Therefore

the coastline characteristics of the harbor area in different scales indicate that the multiscale corner detection method can extract potential harbor areas.Second

an improved jetty detection method is adopted to extract a finer harbor area.Given the inevitable presence of harbor jetties

the detection result can significantly reduce the search range of the SAR image.Moreover

the detection result can further confirm the position of the harbor area.The harbor area based on jetty detection in the potential region is thus extracted.The candidate region of the jetty can be removed using the proposed method

and the exact harbor area can be obtained.Third

the closed-shoreline measurement method is used to eliminate false harbor identification.The presence of several small harbors can easily be a false target.The natural environment of the coastline is complo evaluate the proposed method

two typical harbor SAR images are processed

namely

the Radarsat-2 image of the Yantai Harbor and the TerraSAR-X image of the Visakhapatnam Harbor in India；both images have a resolution of 1 m.In comparison with the method proposed in the literature

the false alarm rate decreased from 10% to 6.6%

and the accuracy rate increased from 91.9% to 93.3%.However

the calculation process is complex

which results in the increase in processing time from 11.58 s to 13.26 s.Thus far

the best detection method has been previously proposed.The study establishes a harbor feature model and proposes a harbor detection method of remote sensing images based on this feature.First

harbor jetty extraction and discrimination is performed based on the instruction of geometric and topological features belonging to the harbor.Subsequently

the jetty key points are selected

and the coastline closure between key points is calculated according to the contextual and geometric features of the harbor.Finally

harbor detection is completed based on the closure principle.The method can easily produce false alarm without coarse-to-fine processing. A new detection scheme is proposed in this study.A complete flow of small harbor detection method is