IMCA Mini RadaScan - Page 27

IMCA M 229 23
The impact of sea reflection on accuracy depends on the region of operation:
Short Range
Medium Range
Long Range
less than 125m
125m to 250m
250m to 1000m
Very little radiation reaches the
sea surface. Reflected image is a
few metres further away than the
direct image and can easily be
rejected
Reflected image is a metre or
two further away than the
direct image. It can usually be
rejected, but it can distort the
direct image
Reflected image is only a
fraction of a metre further
away than the direct image.
The images can’t be separated
No Errors
Occasional Errors
Frequent Small Errors
Table 1 – Sea reflection accuracy summary
11.4.2 Sea Reflection – Typical Operating Conditions
Here are some range and bearing measurements typical of station keeping operations in the
North Sea:
Figure 21 – Range and bearing plots at 70 m – Standard deviation: ≤ 0.085 m
Figure 22 – Range and bearing plots at 70 m – Standard deviation: ≤ 2.41 mrad
The wave motion is fairly strong, making it more difficult to quantify the accuracy performance.
In a comparison with an alternative sensor (e.g. GPS), timing and other registration errors
dominate over Mini RadaScan measurement errors. We can apply a high-pass filter which has
unity gain for white noise while attenuating the wave motion. This gives us an upper bound on
the standard deviation of the range and bearing measurements.