Spark Station 2 ) for image processing later in the laboratory. 
This system can takes the successive images from running car 
with a line sensor camera, and record to a data tape as a digital 
image data, and it is possible to process those data by a 
computer without an analog digital conversion. 
One of most different part between a Video Camera (an area 
sensor camera ) and a Line Camera is, a Video camera records 
a image of area, on the other hand, a Line Camera records a 
image of line, so if the camera would not move, it is scanning 
the same line. For the case of using a Video camera ( an area 
sensor camera ) and a Video Cassette Recorder, it can only 
record 30 frames per one second ( picture of area images : 
NTSC standard ). It means when recording successive 
images, a Video Camera can record 30 lines per one second. 
But for the case of using the Line Camera, according to the 
specifications of the Camera (Table 1. ) and the result of some 
experiments in the field, with using DDR, it is possible to get 
a line of image data ( 512 pixels per a line ) approximately 
10,000 lines of image data can record in one second. 
Table 1. Specifications of the Line Camera 
  
  
  
  
  
  
  
  
PIXEL SIZE 13um X 13um 
LINE SIZE 512 PIXELS 
DOT CLOCK 8 MHz 
DATA OUTPUT 8 BIT DIGITAL 
LINE SCAN RATE 10,000 scan /sec 
  
So, if the Line Camera travels at a speed of 20 kilometers per 
an hour ( 5.55 meters per a second ), a vertical resolution of 
each scan is approximately 0.56 millimeters. ( Figure 2.) 
The other hand, a horizontal resolution just depends on optics. 
If select a Lenz for the Line Camera to take 10 centimeters full 
width object, a horizontal resolution of images becomes 0.2 
millimeters per a pixel dot. 
Table 2. Vertical Resolution of the Line Camera Image Data 
  
  
  
  
VELOCITY LINES / SEC| RESOLUTION 
10 km/hour | 2.777m/sec 10,000 0.28mm 
20 km/hour | 5.555m/sec 10,000 0.56mm 
30 km/hour | 8.333m/sec 10,000 0.83mm 
  
  
  
  
  
  
  
     
  
Gauge Corner 
]-«—— (Inner side of tracks) 
A : Stress by Train weight 
B : Stress by centrifugal force 
( At curved track ) 
C : Stress by Vibration 
Rail Way 
  
  
  
Figure 2. Stresses to Railway 
CHARACTERISTICS OF RAIL SURFACE FLAW 
When trains run on rail way tracks, those wheels force several 
kinds of stresses to rail way tracks. Mainly, those stresses 
are (A)Train weight stress, (B) Centrifugal stress at curved 
tracks, and (C) Hitting force when trains ( or wheels ) are 
vibrating. These complicated stresses make rail way material 
fatigued. ( Figure 2.) So, the vast majority of flaw are break 
out at curved track area. 
In the first stage of fatigue, many small cracks ( very fine 
crack : 0.1 millimeter - 0.3 millimeters ) appear on rail 
material surface ( from the gauge corner side ). In process of 
time, number of cracks are increased and those length are 
stretched to opposite side. ^ Finally, crack reach to deep part 
of rail material, and make it break. 
Practically in filed, when the length of cracks from gauge 
corner side extended over the limit, the surface of rail of those 
parts are ground by the grindstone and removed all fine cracks. 
At the time of maintenance, the condition of the rail surface is 
judged by measuring the length of flaws from the gauge corner 
side. 
WAY TO GET THE IMAGE DATA 
The Line Camera set over the center of Rail in downward 
vertical position. And the scanning line of the Line Camera 
meets traveling direction at right angles. ( Figure 3.) 
  
Line Camera Uint 
   
   
Figure 3. Image of the Line Camera Setting 
  
  
  
Under normal condition, rail surface is possible to distinguish 
two part. One is a polished part like as a mirror by wheels 
( Gauge corner side ), and the other is a rusty part which 
wheels do not touch ( Out side of rails ). 
When an illuminating light set at lower position ( close to rail 
surface ), a rusty part causes diffused reflection. ( Figure 4. ) 
In the Line Camera image data, that area is recognized as a 
bright part. The other side, at a polished part, as every 
reflected light on rail surface dose not reach to the Line 
Camera, in the Line Camera image data, that area is 
recognized as a black part. 
In early time of fatigue, the shape of flaw like as a fine file. 
So, those flaws also cause diffused reflection, in the Line 
Camera image data, those are recognized as bright fine bars in 
a black part. ( Figure 5. ) 
Previous section pointed out, the CCD Line Sensor scans in 
396 
International Archives of Photogrammetry and Remote Sensing. Vol. XXXI, Part B5. Vienna 1996 
  
  
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Figure 6