Agriculture Reference
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Fig. 4.7 ( a ) Stand-alone tower for remote sensing. ( b ) Computer installed at the top of the tower.
( c ) Multispectral camera with motorized zooming. ( d ) Pin-tilt controller. ( e ) Installation at the top
of the tower. ( f ) Motorized lens controller. ( g ) Webcam at the halfway point of the tower
respectively, and 928 steps in total. Exposure time was the amount of time that each
channel in the camera accumulated the charge before the electronic shutter was
closed and the resulting value was read out. The exposure time of the camera varied
from 0.1 to 108 ms that corresponded to 16-bit digital number from 1 to 1,080,
respectively, with 1,079 steps in total. The maximum frame rate of the camera was 10
frames per second. The camera was able to output 8-bit and 10-bit digital image for
each channel. The 8-bit mode and a digital frame grabber IMAQ PCI 1428 (National
Instruments, Austin, TX) was used in the image-acquisition process. The PCI 1428
had been installed into an industrial small rugged computer with PCI expansion slot
(SC241S) that could operate at extreme outdoor conditions. A serial port of the com-
puter was connected to the external control port of the camera via a nine-pin serial
cable. The pan/tilt device was rotated in horizontal and vertical directions to get the
images according to the plot distributions. The Pelco D protocol was used to com-
municate with the pan-tilt device and receiver using RS232 serial communication.
The pan-tilt rotates 0° to 355° horizontally and 0° to 90° degree vertically. The presets
according to the fi eld distribution were established using the caller identifi cations,
and automatic rotations of the pan/tilt device had been developed. The lens motoriza-
tion was developed externally and it used two motors to control zoom and focus.
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