Calibrating the cameras of the TV system for navigation and observation
1. The geometric calibration of TSNN camerasThe TSNN cameras geometric calibration was carried by the autocollimating resection on a special stand.
Stand for TSNN geometric calibration
base 1, the holder of calibrated cameras 2 with adapter 3 for the camera mounting (camera position during installation is shown by dotted line), two plane-parallel mirrors (removable aligning 4 and control 5), two autocollimating theodolites (measuring 6 and control 7) and the attachable high-precision level 8.
Based on the calibration results the following parameters were measured for each camera:
- - focal length
- - position of principal point
- - total distortion
Imaging characteristics of cameras comply with the requirements specifications. The distortion values of cameras are less than one pixel on the entire image field.
2. The radiometric calibration of TSNN cameras
The radiometric calibration of TSNN cameras war carried out on integrating sphere. The calibration included the following measurements:
- - examination of cameras' noise characteristics
- - determination of signal linearity range
- - dark current measurements
- - measurements of absolute sensitivity distribution over the frame depending on the exposure time, gain and videosignal bias
Example of calibrating sensitivity of the TSNN camera confirming linearity of the light-transfer characteristics.
The results of the radiometric calibration of TSNN cameras allow to adjust their sensitivity heterogeneity and to transfer from the digital signal to the values of the absolute brightness of each image pixel.