ns-scaled time-coding method for real-time 3D
super-resolution range-gated imaging
Dezhen Lu (卢德贞), Xinwei Wang (王新伟)*, Songtao Fan (范松涛), Jun He (何 军),
Yan Zhou (周 燕), and Yuliang Liu (刘育梁)
Optoelectronics Systems Laboratory, Institute of Semiconductors, Chinese Academy of Sciences,
Beijing 100083, China
*Corresponding author: wangxinwei@semi.ac.cn
Received March 19, 2015; accepted May 27, 2015; posted online June 26, 2015
We present a method of time coding with ABAB synchronization timing control for real-time 3D super-
resolution range-gated imaging (3DSRGI). To meet the high precision of time delay and pulse width in ABAB
synchronization time sequencing, phase shift is implemented to achieve ns-scaled delay and width accuracy
without restoring to high clock frequencies. Theoretical analysis and experiments prove that 1 ns delay and
width precision is obtained by our timing control unit based on a single field-programmable gate array
with 5 ns clock cycle. Finally, a prototype experiment of 3DSRGI is demonstrated at a 10 Hz video rate with
696 pixels × 520 pixels.
OCIS codes: 110.6880, 150.6910.
doi: 10.3788/COL201513.081102.
High-resolution real-time 3D imaging is urgently need for
spatial navigation
[1]
, spacecraft landing and docking
[2]
, and
topographic surveying and mapping
[3]
. However, the
widely investigated 3D flash LIDAR has a low resolution
that cannot satisfy some high-resolution applications in
dynamic environments. For instance, NASA’s Autono-
mous Precision Landing and Hazard Detection and Avoid-
ance Technologies (ALHAT) project has determined that
a single frame of a 3D image generated by the current
state-of-the-art 3D flash LIDAR may not be sufficient
to build a landing site digital elevation map with accept-
able spatial resolution, precision, and area coverage
[2]
.3D
range-gated imaging (3DRGI) is a new prominent tech-
nique of remote sensing with a higher resolution than
3D flash LIDAR
[4]
. The current 3DRGI has been mainly
developed with two approaches: time sliding and super-
resolution. For the method of time sliding, 3D scene
reconstruction is achieved in a post-processing procedure
using hundreds of sliding gated delay time 2D images
[5,6]
,
which has bad performance in real time. 3D super-
resolution range-gated imaging (3DSRGI) can reconstruct
3D images from a minimum number of two 2D range-
gated images
[7–11]
, which has potential for real-time 3D im-
aging. In this Letter, we propose a time-coding method to
realize real-time 3DSRGI where the range-gated imaging
system is synchronized by an ABAB synchronization tim-
ing control. However, the current time delay and pulse
width precision are governed by the clock frequency of
a field-programmable gate array (FPGA)
[12–14]
, which is
the preferred option used to realize the synchronization
timing for reliability, independence, and system integra-
tion reasons. To overcome the synchronization problems,
we propose a phase-shift method to improve the time
delay and pulse width precision to a ns-scale by a single
FPGA. Computer modeling experiments and prototype
field tests are conducted to confirm the improvement of
synchronous control precision and real-time performance
of time coding 3DSRGI.
In 3DSRGI, each la ser pulse triggers a camera with a
highly sensitive gate, so that a number of laser pulses
are integrated on a CCD and a CCD eventually produces
a 2D gate image. As depicted in Fig.
1, to realize real-time
3DSRGI, sequences of time coding 2D images (ABAB…)
are recorded by a synchronization timing of ABAB mode
which is generated by a timing control unit (TCU) to syn-
chronize the laser and the gate as well as the CCD. Under
the ABAB synchronization timing sequence the corre-
sponding time-coding images of targets are output and
the two consequent frames inevitably contain a gate image
Fig. 1. Principle of the time-coding method in 3DSRGI.
COL 13(8), 081102(2015) CHINESE OPTICS LETTERS August 10, 2015
1671-7694/2015/081102(5) 081102-1 © 2015 Chinese Optics Letters