Centre for Remote Imaging, Sensing and Prcessing (CRISP)

CRISP's Research

Contact: crisp@nus.edu.sg Copyright © CRISP, 2001

Ship Detection by Synthetic Aperture Radar

Synthetic Aperture Radar (SAR) is a valuable tool for monitoring ships because of its all-weather, day/night capabilities, and its wide coverage area. Much information about detected ships can be derived from the SAR image, including the ship's location, heading, length, velocity, and possibly shiptype.

Ships in SAR Images

Ships appear as bright objects in Synthetic Aperture Radar (SAR) images because they are strong reflectors of the radar pulses emitted by the satellite. In images with finer resolution, such as the RADARSAT image shown above, it is even possible to discern the structure of ships, making it potentially possible to identify ship types.

Ship Wakes in SAR Images

Many types of wakes can be seen in SAR images, depending on the ambient and imaging conditions. These include turbulent wakes, Kelvin envelops, transverse waves, internal wave wakes, and narrow-V wakes[LINK TO PAGE ABOUT SHIP WAKE OBSERVATION].
Kelvin wake Bright turbulent wake Stern waves

In SAR images, moving ships are displaced from their wakes due to an effect known as the Doppler Effect. The wakes and their displacement further provide estimates of the ships’ velocity.

This ERS SAR image shows two ships moving in opposite directions in the Malacca Strait. Both ships are displaced vertically from their dark turbulent wakes. Calculations yield values of 6 and 12.5 m/s for the speed of the left and right ships respectively.

CRISP’s Ship and Ship Wake Detection System

CRISP’s ship and ship wake detection system can process both ERS and RADARSAT images, and produce visual and textual information about the detected ships, such as the location, speed, heading, length and wake type of each ship.

Sample Graphic Output

The detected ships are highlighted in purple in this sample graphic output of the ship detection system. Large clusters of ships can be seen in the docking areas. The yellow regions in the image indicate mainly land areas which were masked out by the system.

A close-up of a graphic output shows the detection results more clearly. Detected ships are coloured cyan and highlighted by purple circles, while detected wakes are indicated by wake lines. Calculated ships headings are also marked. The detected ships in the image are annotated by numbers. The information about the ships are given in the textual output.

Textual Output

The textual listing provides detailed information regarding the ships, including its location, speed, heading, length and wake type. It also contains information about the image itself, such as the latitude/longitude, time/date, and satellite incidence angle etc.

Copyright © CRISP, 2001