IEEE - Aerospace and Electronic Systems - January 2020 - 10

Feature Article:

DOI. No. 10.1109/MAES.2019.2956801

Calibration Method of Laser Detection System With
Position Sensitive Detector
Tan Ju, Jiyan Yu, Chao Ming, Xiaoming Wang, Xiaohui Gu, Nanjing University
of Science and Technology, Nanjing, China

INTRODUCTION
THE LASER-GUIDED weapons have strong anti interference ability and high precision, and have been widely
studied by the military in various countries and applied to
the contemporary wars [1]. The key part of the laserguided weapon is the strapdown LDS. And the LDS is
mainly composed of laser detectors and optical lenses. A
laser detector is a light spot converter that converts the
light spot into an electrical signal so as to obtain coordinates of the light spot. Common photoelectric conversion
devices include four-quadrant photo-detectors, chargecoupled image sensors, and one position sensitive detector
(PSD). The PSD has the advantages of continuous measurement, high sensitivity, high position resolution, and
fast response, which makes it widely used in the field of
photoelectric measurements.
The PSD is widely used in both civilian and military
fields because of its several advantages. In civilian applications, the PSD is used to measure the microangle of the
microswing mirror [2], the flatness of the object online
[3], the microdisplacement [4], the bar deflection [5], and
so on. In military applications, the PSD is used to measure
the roll angle of the projectile [6], determine target localization relative to the projectile [7], and study the probability of target acquisition [8], [9]. The authors focus on the
application of the PSD in the military field, so three concrete application examples will be described in detail in
the following introduction. The first example is introduced
in [6], which is a measurement method of projectile roll
angle using the PSD. This method requires the GPS to

Authors' current addresses: Tan Ju, Jiyan Yu, Chao Ming,
Xiaoming Wang, Xiaohui Gu, Ministerial Key Laboratory
of ZNDY, Nanjing University of Science and Technology,
Nanjing 210094, China E-mail: (jutann@163.com).
Manuscript received September 20, 2018, revised
November 15, 2019, and ready for publication
November 27, 2019.
Review handled by P. Willett.
0885-8985/19/$26.00 ß 2019 IEEE
10

provide auxiliary information to calculate the reference
value of the projectile roll angle. Combined with the measurement of the PSD, the projectile roll angle is then
solved. The other example is to determine target localization
relative to the projectile. There are two crucial parameters in
the LDS with the PSD, one being the projectile attitude, and
the other the relative position between the projectile and the
target. If the projectile attitude is unknown, it is difficult to
get the relative position between the projectile and the target, but the field of view can be obtained by the measurement of the PSD. In order to get the relative position
between the projectile and the target, taking the optical axis
as the center line, a conical surface can be established.
Then, an ellipse can be obtained when the conical surface
intersects the ground plane. Although the position of the target is unknown, the target must be on this ellipse. Three
ellipses in the consecutive moments will intersect at one
point, and the intersection point is the target [7]. Although
the field of view can be obtained by the measurement of the
PSD, the detectable angle range of the system is limited. So,
it's hence necessary to study the target acquisition probability. An extended-range individual rocket was studied in [9],
the optimum initial detection point was established with
considering the target acquisition probabilities at different
positions in the terminal trajectory. In order to improve the
target acquisition probabilities in the terminal trajectory of
the mortar projectile [8], the launch angle is taken as the
optimization variable.
The PSD is an excellent photoelectric converter, but it
also has some disadvantages. Due to the uneven resistance
in the sensitive layer, the difference in electrode structure
and the edge effect, the PSD has serious nonlinearities, so
that its output values cannot correctly reflect the actual position of the incident light spot [10]. In order to improve the
measurement linearity of the PSD, methods of improving
the structure of the PSD and improving the manufacturing
process of the PSD are studied. However, the benefit-cost
ratio diminishes. On the other hand, low cost, high-precision
mathematical calibration methods have become more and
more popular, such as Newton interpolation [11], BP neural
network [12], LM-BP network with the genetic algorithm

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