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Automatic Direction Finding
Localization –> Config Localization
Localization Area
The localization algorithm of the SignalShark is based on a matrix that represents a
rectangular area on a geographic map. Each element of the matrix represents a discrete
position on the map. The element values are related to the probability that the suspicious
transmitter is located at the assigned geographic position.
The probability values are normalized to the maximum value of the matrix, color coded, and
displayed as an overlay on the geographic map. This matrix is therefore called a localization
heatmap. Red areas denote likely and blue areas unlikely locations of the suspicious
transmitter.
The entire heat map is recalculated for each new bearing to make a new estimate of the
location of the suspicious transmitter. It is important that the heat map area selected is large
enough to ensure that the suspicious transmitter is located within it. The heat map area is
highlighted on the geographic map and can be adjusted as desired.
It is possible that the transmitter position will be outside the heat map if the area selected is
too small. In this case, the localization process must be stopped, a new heat map area
selected, and the heat map recalculated for bearings already taken. This can be time-
consuming if thousands of bearings have already been taken. It is therefore recommended
that a heat map area that is probably oversized should be selected from the outset.
By taping on "Set Localization Area", the visible map section will be used as localization
area.
You can change the area by setting the parameters "Upper Border", Lower Border, "Left
Border" and "Right Border". After this you have to apply the changed settings be tapping
again on "Set Localization Area".
"Velocity Squelch"
The "Velocity Squelch" parameter is important for homing-in drives. It prevents possibly large
bearing uncertainties that are due to large uncertainty in the GNSS velocity direction at low
speeds or when stopping.
It should be set to a value of about 10 km/h if the average driving speed is much higher than
10 km/h. A lower squelch value may be necessary if the traffic situation does not allow
average speeds above 30 km/h.
"min. DF Quality"
The parameter "min. DF Quality" can be used to discard bearings that have low DF quality
values. The DF quality is defined in the section Bearing View –> "min. DF Quality". In
contrast to the Bearing View, this value can be changed in the Map View even after data is
saved.
The DF quality of useful bearings is often greater than 70%. However, it is better not to
discard low DF quality bearings if this means that too few bearings are available.
"LOS Prob." and "Bearing Error"
The SignalShark uses an innovative maximum likelihood algorithm for the localization of
transmitters. The algorithm assumes a certain probability for line of sight situations. It is
assumed that, in these line of sight situations, the probability density function (PDF) of the
bearings is Gaussian, with a mean value of the true AoA and an assumed standard
deviation.
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