A localization is based on bearings. These bearings can be measured manually (e.g. by using the antenna handle and an appropriate antenna) or automatically with the ADF antenna. Depending on the Auto Localize setting the localization can be calculated automatically or triggered manually. All settings needed for localization can be found in the Localization menu.
Specifying the localization area reduces the amount of localization calculations.
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.
1. Set the view window to the desired size and zoom the map to the planned localization area.
2. Tap the Set to current Map Margins button.
The displayed map area is superimposed by a transparent red layer.
The map can still be zoomed in / out and centered.
3. If needed adapt the red marked localization area by dragging the arrows at the window edges to the desired position.
If the localization area was set by using the map (see above), the coordinates are automatically set accordingly. Instead of using the arrows on the window edges you may also enter the coordinates to adjust the area. Or you may set the coordinates from the scratch without presetting the area by means of the map.
Tap a button to enter a margin.
The heatmap resolution is a factor that relates the heatmap grid to the pixel resolution of the slippy map tiles. By default, the spatial resolution of the heatmap is the same as that of the slippy map tiles at the zoom level used when the heatmap area is selected.
The spatial resolution can also be set to values between 1/4 and 4 times the default resolution.
The use of relative spatial resolutions down to 1/4 is recommended if a very large area is selected. The default value of unity is a good choice for medium-sized areas. Values higher than unity make sense if a very high resolution external display is used to make the selection.
When using a high zoom factor (e.g. 15), 1 pixel is sufficient. When using a low zoom factor (e.g. 9), a higher resolution would be recommended (e.g. 1/2) to show details even if the display is enlarged for later evaluation.
Tap to select an entry from the dropdown list.
For a quick and easy setup, the settings for the most common application are stored in these presets. Following presets are available:
• City - Vehicle - GNSS: In the city with a (moving), based on GNSS data
• City - Fixed Site (Tripod, Mast): In the city with a fixed antenna
• Free Field - Vehicle - GNSS: On the open field with a (moving) vehicle, based on GNSS data
• Free Field - Fixed Site (Tripod, Mast): On the open field with a fixed antenna
• User Defined: This label is displayed if one of the presets is changed. It only shows the change but does not allow to store the changes in a user defined setting.
Tap to select a preset from the dropdown list.
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.
Equal distribution over the complete azimuth range is assumed for non-line of sight situations. In this context it should be noted that a line of sight situation does not necessarily mean that there actually is a line of sight between the direction finder and the transmitter. It is sufficient that the bearings in these situations have a PDF that roughly approximates to the assumed PDF. In other words, a line of sight situation is one where the bearings still correlate with the true AoA. Conversely, a non-line of sight situation is defined by the absence of any useful information in the bearings.
The user must enter settings for both parameters of the model. The SignalShark user interface uses the terms LOS Prop. for the assumed probability of line of sight situations and Bearing Error for the assumed standard deviation of the useful bearings.
Under ideal conditions, the Bearing Error should be set to the RMS value of the DF uncertainty specified in the DF antenna data sheet, and LOS Prop. should be set to 100%.
More realistic scenarios take the uncertainty in the north reference and the bearing uncertainty due to multipath propagation into account in the “Bearing Error”. Evaluation of homing-in tests conducted by NARDA using the ADFA-1 with transmitter frequencies of around 950 MHz shows that a “Bearing Error” between 5° and 10° and a LOS Prop. of 50% describe a good approximation of the true PDF of the bearings taken during homing-in drives in moderate urban environments. Note that the Bearing Error and LOS Prop. values are not critical for the rate of convergence and the accuracy of the localization algorithm. However, they do have a significant influence on the assumed localization uncertainty, which is displayed as an uncertainty ellipse around the estimated position of the transmitter. If realistic parameters are entered in the model, the ellipse will delineate the area where the transmitter is located with a probability of 95%.
Tap to enter a value in percent.
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.
Equal distribution over the complete azimuth range is assumed for non-line of sight situations. In this context it should be noted that a line of sight situation does not necessarily mean that there actually is a line of sight between the direction finder and the transmitter. It is sufficient that the bearings in these situations have a PDF that roughly approximates to the assumed PDF. In other words, a line of sight situation is one where the bearings still correlate with the true AoA. Conversely, a non-line of sight situation is defined by the absence of any useful information in the bearings.
The user must enter settings for both parameters of the model. The SignalShark user interface uses the terms LOS Prop. for the assumed probability of line of sight situations and Bearing Error for the assumed standard deviation of the useful bearings.
Under ideal conditions, the Bearing Error should be set to the RMS value of the DF uncertainty specified in the DF antenna data sheet, and LOS Prop. should be set to 100%.
More realistic scenarios take the uncertainty in the north reference and the bearing uncertainty due to multipath propagation into account in the “Bearing Error”. Evaluation of homing-in tests conducted by NARDA using the ADFA-1 with transmitter frequencies of around 950 MHz shows that a “Bearing Error” between 5° and 10° and a LOS Prop. of 50% describe a good approximation of the true PDF of the bearings taken during homing-in drives in moderate urban environments. Note that the Bearing Error and LOS Prop. values are not critical for the rate of convergence and the accuracy of the localization algorithm. However, they do have a significant influence on the assumed localization uncertainty, which is displayed as an uncertainty ellipse around the estimated position of the transmitter. If realistic parameters are entered in the model, the ellipse will delineate the area where the transmitter is located with a probability of 95%.
Tap to enter a value in percent.
Velocity Squelch 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.
Tap to set the squelch.
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.
To set the value:
Tap the button and select a value from the dropdown list.
Select Off to accept all bearings for calculation.