Smart Camera System
--Andrew Wilson
The detection and measurement of ice on aircraft is crucial to pilots during flight and also before takeoff to assess deicing requirements. To make such measurements easier, engineers at Canpolar East (St. John`s, Newfoundland, Canada) have developed a smart-camera-based remote ice-thickness measurement system using a laser diode and the company`s VE-262 Smart Camera.
The Smart Camera is a complete vision system. It contains a built-in 486-based personal computer, a digital signal-processing frame grabber, a hard disk, a VGA video card, and a communications interface. The system is programmed to perform the ice-thickness measurement using a graphical user interface produced by the company`s VE-Tools software. For remote measurements, the company`s DSP-based VE-262 video camera with a telephoto lens is used.
The measurement technique makes use of the refractive property of ice, or liquid, to remotely detect and measure its thickness on a surface. During operation, the system laser is aimed at the aircraft surface on which a layer of ice is present. Reflected images show a bright spot where the laser first strikes the surface, a dark circular region, and a lighter region where laser light is scattered before reflection. Measuring the diameter of the dark region determines the ice thickness.
To extract the diameter value of the darker ring, the system first removes the noise on the captured images using a 3 ¥ 3 median filter that is applied five times. Then, the separation between the darker and brighter regions is accomplished by growing the brighter area of the image with a gray-scale erosion operator and next growing the darker region back with a gray-scale dilation operator. The image is binarized, and one iteration of a binary opening operation is applied to eliminate single-pixel objects. Lastly, blob analysis is performed on the image, and features such as the length of blob in the x-direction are extracted.
Once the diameter of the darker region is calculated, the ice thickness is computed using a geometric analysis. According to Canpolar, in laboratory tests, the system provides a measurement accuracy of about 0.1 mm for an ice thickness of up to 1 cm.
