CHAPTER 3
5
SENSOR CHARACTERIZATION
A collimated beam was directed perpendicularly upon the sensor.
The response of the sensor was recorded in air and in distilled water at
discrete water depths.
The response in water relative to the response in air in dependence
of depth was fitted with a least squares regression line and extrapo-
lated to a depth of 0 mm (see Fig. 3).
immersions
y = -0.0003x + 0.5613
R
2
= 0.9932
0.53
0.54
0.55
0.56
0
20
40
60
80
1
water depth (mm)
re
s
p
o
n
s
e
in
wa
te
r r
e
la
ti
ve
to
respo
nse i
n ai
r
00
Fig. 3:
Determination of immersion factor
The obtained relative response for zero depth was corrected for
2% radiation loss at the air-water interface. The reciprocal of the ob-
tained value results in the immersion correction factor given in the
calibration certificate. For example for the regression line shown in
Fig. 3 the immersion correction factor is 1.75.
For more information on the dependence of the immersion factor
on the refraction index
see
Austin (1976) and the refraction index of
the sea water,
see
Austin and Halikas (1976).
The immersion factor in the calibration certificate is given for dis-
tilled water.
