(1) Laser emitting sub-system: TPGAS2S09H diode 
laser with wavelength of 905 nm is used for this 
project. This laser emitting sub-system is to 
generate high energy of laser. As a initial 
research, a prototype with 5 x 5 pixels2 3D image 
array with <5cm ranging accuracy, in real time at 
rates up to 30 Hz, is designated. 
(2) Receiver sub-system: The most common detector 
used to detect the laser echo pulse is linear mode 
avalanche photodiode (APD). This research 
adopted the Geiger-mode APD for receiving 
photon single. 3D imaging laser radar that uses 
Geiger-mode APDs is being developed (Aull and 
Marino, 2005; Daniel, 2003; Johnson, 2003; Aull 
et al., 2002; Marion et al., 2003). Because of the 
effect of background light noise, a new system 
design and new data processing method need to be 
developed. The details of this sub-system will be 
reported in the near future. 
(3) Micro-Control Sub-system: which is core of 
system. The microprocessor controls the entire 
system and enables real-time control laser 
emitting, receiving, measure of time interval, data 
sampling, storage, etc. The control device also 
provides interactive communication with each 
modules. The control device is, therefore, usually 
designed as keyboard display unit. 
(4) POS subsystem: which is used to provide the 
attitude of each laser ray and central position of 
laser emitter for calculation of 3D geodetic 
coordinates in a given coordination system. 
(5) LiDAR point cloud pre-processing: which is used 
to generate XYZ coordinates on the basis of range, 
attitude angles of each laser ray and central 
coordinates of laser emitter. 
2.2 Principle of Flash Laser Emitting 
A detail of principle for flash laser is given by Hu (2005). 
A brief description is given in this Section. 
If the size of the emitting plan of a diode laser is 
L and L, in length and width, and the divergence angle 
of the bundle of lasers is g , and 9, in horizontal and 
vertical plan, the focal length is f,, the laser source is 
located at the focus (see Figure 2). 
With geometry in Figure 2, we have 
60, = 2arctan( L ) (D 
  
t 
Generally, L << 2 f;, so the divergence angle of plan is 
a eis (2) 
Ff, 
As observed in Eq. 2, the divergence angle is negatively 
proportional to the focal length. 
International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences, Volume XXXIX-B3, 2012 
XXII ISPRS Congress, 25 August — 01 September 2012, Melbourne, Australia 
To make the direction of emitting laser is parallel to the 
direction of entry laser, the diameter of aperture must be 
at least 
D, zL, 4 2f, an) (3) 
Usually, L << D,, , the least diameter of aperture is 
expressed by 
D, «2f, tan (4) 
So, the least width of laser plan is 
D -—D,-L £5) 
Substitute Eq. 3 into Eq. 5, we have 
D, =2f tan) (6) 
As observed from Eq. 6, the width of laser plan is 
positively proportional to the focus length. 
Combined Eq. 2 and Eq. 6, it is hard to simultaneously 
meet both conditions, which results in difficulty of 
designing a reasonable and powerful laser emitter sub- 
system. 
With the same method, we have divergence angle is 
2.5 (D 
t 
To make laser power in the emitting system in vertical 
plan, the least diameter of aperture is 
BD RAF tan) ( 8) 
The least width of emitter laser in vertical plan is 
D,, = 2f, tan) (9) 
For example, if the emitter plan is 225x400um, the 
divergence angle is 10° in planar direction and 25° in 
vertical direction, and divergence angle is 30-33mrad 
after alignment. 
With the two cases above, this paper select the fast —axis 
conical lens with a focal length of 7.7 mm, and 7 mm and 
9 mm in height and length; select a slow-axis conic lens 
with a focal length of 13.7mm, and 13 mm and 15 mm in 
height and length. 
The major purpose of the emitting system is to align the 
emitting laser. Thus, when selecting an emitting laser 
system, we have to simultaneously consider both the 
alignment characteristic and the complexity of optical 
system in structure, processing and manufacturing. With 
the computational parameters, the 3D model is simulated 
using ZEMAX software, as depicted in Figure 3. The 
simulated 3D model, associated with its size is depicted 
in Figure 4.