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Question 1

Describe the principle of hyperbolic radio positioning.

Answer 1

The master (ship) and the slave(s) stations are synchronized and send continuous waves. The phase difference between the signals helps determine the distance difference, creating hyperbolic L’OPs.

Question 2

Describe the principle of circular radio positioning.

Question 3

Describe the principle of polar radio positioning.

Answer 3

Active (SU): Coastal stations determine the vessel’s direction using a radio-goniometer. The pulse is transmitted to the vessel, and distance is determined through signal timing, with high accuracy due to the orthogonal intersection of LOPs.

Question 4

Describe the principle and types of inertial systems.

Question 5

Describe the principle of Doppler-effect based systems (e.g. ADCP systems).

Question 6

Are hyperbolic/circular/polar radio positioning systems active or passive systems ?

Answer 6

Hyperbolic system: Passive (the vessel or receiver only receives signals from multiple coastal stations, with no active transmission).

Circular system: Can be both active (if the vessel sends a signal to the coastal stations) or passive (if the vessel only receives signals from the stations).

Polar system: Active (the vessel transmits and receives signals from coastal stations, typically for single-user systems).

Question 7

What are disturbing factors for acoustic waves ?

Question 8

Explain: transducer, interrogator, pinger, responder, hydrophone, transponder,…

Question 9

Describe how active (and/or passive) LBL can be used ?

Question 10

Describe how active (and/or passive) SBL can be used ?

Question 11

Describe how active (and/or passive) USBL can be used ?

Question 12

How to compute, visualize and assess the precision of positioning ?

Answer 12

1. Compute Precision
   * Measure deviations: Calculate the difference between individual measurements and the average position.
   * Quantify random errors: Use:
   o Standard Deviation (SD) to measure spread.
   o Boxplot to show 25%-75% limits (the middle 50% of data).
   o CEP (Circular Error Probable): The radius where 50% of points fall (used in military).
2. Visualize Precision
   * Boxplot: Displays the range between 25%-75% and the spread of measurements.
   * Scatter Plot: Shows how closely measurements cluster around the average position.
3. Assess Precision
   * Smaller errors = better precision: Tight cluster of measurements means good precision.
   * Error metrics: Look at SD, Boxplot limits, or CEP to evaluate how close the measurements are to the average.

Question 13

How to compute, visualize and assess the accuracy of positioning ?

Answer 13

Compute Accuracy:
* Systematic Error (Bias): The difference between average measurements and the ‘true’ position.
* True Value Approximation: Use the mean, median, or mode as an approximation.
* Visualize Accuracy:
* Gaussian Curve: Shows the mean of data.
* Frequency Graph: Displays the most frequent value (mode).
* Boxplot: Shows the median and spread.
* Assess Accuracy:
* Error Sources: Caused by calibration issues or wrong models.
* Solutions: Calibrate sensors or adjust models.
* Repeatability: Same errors in repeated measurements don’t help detect bias.

Question 14

What is the difference between repeatability and reproducibility ?

Question 15

What defines the accuracy and/or precision of active/passive circular range/range radio
positioning systems ? Can you give a model for the geometric quality of the positioning ?

Answer 15

Geometric quality for circular system is defined by a Line of position distancing with the length D from the Station. This circular area is create by the radio wave the circle is equal to the range of the station.

The quality of a circular systems will depends of the crossing angle between 2 different’s LOP. It’s
better if the 150°>angle>30°.

AB= Base Line
Small Base Line= Small circles = Good Area
Long Base Line = shaded area is increased so bad positioning area is increased.
Optimal intersection between 2 LOP.

Question 16

. What defines the accuracy and/or precision of hyperbolic radio positioning systems ? Can you
give a model for the geometric quality of the positioning ?

Answer 16

the accuracy and precision of a hyperbolic positioning system depend on factors like the intersection angle of the hyperbolas, the lane width, and the distance from the baseline. Optimal performance is achieved when the intersection angle is near orthogonal and the distance is kept within reasonable limits relative to the baseline length.

Angle of Intersection:
* The angle at which the two hyperbolas intersect is crucial. The best positioning accuracy occurs when the hyperbolas intersect at a near-right angle (90 degrees).
Cutting Angle:
* The angle between the two stations (slaves) affects accuracy. Smaller angles lead to larger errors, while larger angles (closer to 90°) give better precision.
Lane-Expansion Factor (K):
* As you move farther from the baseline, the “lane” (range of possible positions) becomes wider, reducing accuracy. The closer the intersection angle, the narrower the lane, and the higher the accuracy.
Error Model:
* The maximum error in positioning is calculated using the intersection angle and lane-expansion factors. This helps determine how much error exists in the final position.
Accuracy:
* Accuracy is generally 1/100th of the lane width. Smaller lane widths (due to better angles and higher frequency) lead to better accuracy.

Question 17

What defines the accuracy and/or precision of polar radio positioning systems ? Can you give a
model for the geometric quality of the positioning ?

Question 18

How to perform the calibration of a radio positioning system (including the assumptions made) ?

Question 19

What is the effect of antenna height differences between rover and reference ?

Question 20

How to check the calibration of circular positioning systems (calibration principles, baseline
crossings,…) ?