OST 1 Spt rials ences. V /. Par. 2004
International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences, Vol XXXV, Part Bl. Istanbul 2004
Control module
TRANSMIT-RECEIVE MODULE
Laser »| AOM P| Telescope
«—]1
Photo- =
| detector ['* Scanner = =
TTT
[12 dio axils DADL -2
DADL -1
Impulse
generator
Delay time | ]
measurement |
RADIO-FREQUENCY MODULE
Y RECOGNITION MODULE
| Special processor >| Onboard comput It —
3
| Onboard control system |
Figure 1. Distance measurement system based on linear FM with pulse compression.
n is the number of an image element (number of sensing) in a
line;
Vaäop is the Doppler velocity along a direction of a laser beam;
& is a delay time measurement error.
Mean square deviation of an error &, depends on value of a
signal/noise ratio on an output of radio-frequency module of
laser locator and can be expressed in a first approximation as
follows [Dansac, J., Meyzonnette, J. L., 1985]:
1
3, Ym (3)
AF A Aj Aw
A is intensity of the received signal;
Ay is average intensity of noise.
Table 1 shows how mean square deviation £, depends on the
signal/noise ratio in case of sensing of a frontal plane, and
corresponding to it values of mean square deviations of
measurements of distance and velocity.
TaOz.1.
A/AN Ô(& 2 ) € ô(R) M 0(V)M/c
10 0.8-10°* 17 0.6.10"
15 0.65105 1.4 0.5.10!
20 0.56.10 1.2 0.42.10!
50 0.35-10* 0.75 0.2610"!
In reality, accuracy will be noticeably worse as scanning is
carried out continuously and resolving of range/velocity
uncertainty is made by results of sensings of different regions of
a surface which can lie on essentially different distances.
THE METHOD DESCRIPTION
The way of processing of the delay times sequence is suggested,
that allows to increase accuracy of vehicle own velocity
measurement, with a’ simultaneous possibility of distance
measurement on each sensing. For this purpose it is possible to
use that fact, that value of vehicle own velocity is slowly
varying function, whereas time of scanning of one line does not
exceed 0.01 s.
Therefore, to increase accuracy of velocity measurement it is
possible to accumulate and average information on each line. At
that it is possible to consider velocity to be constant during a
line. Then having averaged value of velocity with use of all
sensings on a line, it is possible to calculate distances in each
clement of a previous line. In practice, however, it is more
convenient to calculate distances for each element right after
information is received. To do this, it is necessary to make
extrapolation of velocity value for the period of the next line,
and to calculate distances for each sensing based on this value.
Thus, two loops of calculation are formed: a vehicle own
velocity calculation and oscillator management loop; and a
distance calculation on elements of a line of sensings and image
transformations loop.
Let's obtain necessary expressions. Doppler shift of frequency
AF yp is determined as
2V
AF o = =
where À is radiation wave-length; Vy is radial velocity.
To maintain system mode of operation in an operating range the
part of Doppler shift of frequency is compensated by radio
heterodyning. Then the signal delay time, caused by Doppler
effect and heterodyning, is expressed as
Internationdi
dop -—
Where AF
cycle; Fie
horizontal vi
beam
Total delay t
up to probec
the second p
happens wit
decreases du
Thus
+ —
Le =
f del —
E
From here 1
À
y -—
2
for section o
Processing !
Let's consic
operates.
1. By result:
vehicle own
At that, for
considered i
1S NO receive
sensings are
the current «
passed thres
compensate
on the surf:
example, at
building to 1
1.e. when no
