User's Manual

LX-80 User Manual
Page 11 of 32
Instrument radar beam covers a circular area on the water surface and works best
when water surface is calm and not wavy because flat surfaces reflect radar beams the
best. As radar beam is defined by 3 dB width angle, the diameter of the pattern on the
water surface is dependent on the distance of the water surface to the instrument.
Calculation of the size of circular pattern on the water surface is calculated and presented
in the table below the text.
Height [H]
R [m]
0.3 m
0.02
0.5 m
0.03
1 m
0.07
2 m
0.14
3 m
0.21
4 m
0.28
5 m
0.35
6 m
0.42
7 m
0.49
8 m
0.56
9 m
0.63
10 m
0.70
11 m
0.77
12 m
0.84
13 m
0.91
14 m
0.98
15 m
1.05
Water surface direct below the sensor should be clean of vegetation, rocks, sand
deposition or other obstacles that could affect measurement. Distance measuring sensor
in the instrument is designed to detect and eliminate obstacles from the distance
measurement signal spectrum but algorithm has limits and ability to discard obstacles are
even more limited in presence of vibration on the instrument mounting. The best results
will be achievable if measurement location is selected in the recommended way.
Slight up to moderate surface waviness will affect the measured signal level, usually
reducing SNR (Signal to Noise Ratio) but will most probably not affect measurement
accuracy. Strong turbulent flow with high water waviness will reduce accuracy due the
unpredictability of the water surface but averaging effect along the radar beam covered
surface will happen and will reduce oscillations. If measured level is highly turbulent, length
of the radar filter can be adjusted to filter out most, if not all the turbulences.