<< Click to Display Table of Contents >> Navigation:  Help Content > Basic Module > Moving Target Detection > Basic -  Feature Extraction - Velocity

Purpose

 

This tool estimates the speed of moving targets in SAR imagery based on the visible displacement between the moving object and the location where it should be (road, track...).

 

Technical Note

 

A moving object along the range direction (i.e. orthogonal to the flight direction) creates an additional Doppler effect (positive or negative depending on whether the object is approaching or moving away from the satellite) on the backscatter of the moving object.

This additional Doppler, during the focusing process, causes the object to be positioned at a different location along the azimuth direction (along which antenna synthesis is performed by exploiting the Doppler of returns). Therefore, by measuring the difference in the object's position relative to what is assumed to be its true position (for example, a car that should be on the road but is above or below, or a train or ship relative to its wake at sea) in azimuth, you can deduce its velocity in slant range.

After that, with simple trigonometry, you can project the object's velocity back along the direction of motion (the road, the rail, the wake in the sea).

Therefore, by plotting 3 points: 2 to define the segment along the road/railway/marine wake, and 1 for the "mispositioned" object in azimuth. It is possible to obtain the velocity along that segment.

The velocity along the azimuth (satellite flight direction), on the other hand, cause the 'defocusing' effect of the object (the point target appears spread across multiple pixels). This type of movement causes the rainbow effect shown by the MTD tool.

Interface overview

 

Units

Define the speed units.

 

Annotations

Define the color of the points defined by the user.

 

Help

It opens the Velocity Help page.

 

Run the tool

Press the Start button to begin.

 

The Velocity Estimation tool consists of two phases:

•Open a _pwr image in the ENVI view and then run the SAR Velocity Estimation Tool. Select the _pwr layer and click on the Start button.

•Use the left mouse button to define two points located on the road or track where the moving object should be. then follow the instruction:

oDefine the First point and the second point.

oThe Reference line has been defined. Now click where the moving target actually is. Its speed will be estimated and displayed.

 

Output Files

 

Displayed outputs

An annotation layer showing the direction and the speed of the target will be displayed.

 

References

Stefan Hinz et al (2005): ''Spaceborne Traffic Monitoring with Dual Channel Synthetic Aperture Radar – Theory and Experiments''.