VEMCO – VR100 Receiver Operating Manual – Page 49
5.2 DETECTION PARAMETERS
The detection parameter levels are used to determine how a real signal, referred to as a detection, is
distinguished from background noise. The VR100 constantly receives a signal similar to the one shown in
the drawing below. This usually includes a large amount of background noise from sources such as noises
in the hydrophone’s environment, electronic components in the receiver, etc. A “cut-off” level must be
selected to decide what is a genuine detection and what is a spike in the background noise. A spike in the
background noise that is mistakenly identified as a detection is called a “false-detection”. The VR100
allows the user to select one of three levels to be used to determine what is considered a genuine detection.
These levels are Near, Norm, and Far.
1.
NEAR
: This is the “safest” detection level because it rejects anything that could be noise, nearly
eliminating false-detections. Unfortunately, it may reject fainter signals that are real. In the sketch
below, everything over the “Near” line is considered a genuine detection. In this case, only one
signal (the first one) was accepted. The other four signals were incorrectly considered to be
background noise and weren’t included. Use the “Near” level when the “Norm” level is receiving
too many echoes. This can happen when the tags are in an enclosed area like a tank.
2.
NORM:
This is the medium level. It rejects some noise but also allows some noise to be mistaken
as detections (false-detections). This level will correctly accept more detections than the “Near”
setting but will still mistake some genuine signal as background noise. In the sketch below,
everything over the “Norm” line is considered a genuine detection. In this case, four signals were
accepted – the first three were genuine detections and the last was noise. Use the “Norm” level for
general use.
3.
FAR:
This level has more false detections. All genuine detections will be accepted, but a larger
number of false-detections will also be accepted. In the sketch below, everything over the “Far”
line is considered a genuine detection. In the sample below, eight detections were reported but
only five of them were genuine detections. The other three detections were actually noise (false-
detections). Use the “Far” level when the tags are far from the hydrophone and the signals
received from the tags are weak.
NOTE: This example has been exaggerated for illustration purposes. In most cases there
will be no false detections with Near or Norm, and very few with Far.
