ESTIMATION
OF
POSITIONING
ERROR
FROM
AN
ARRAY
OF
AUTOMATED OMNIDIRECTIONAL RECEIVERS IN AN ARTIFICIAL REEF
AREA
Giacalone V.M.1, D’Anna G.1, Garofalo G.1, Collins K.2, Badalamenti F.1
1
Laboratorio di Biologia Marina, IAMC-CNR, 91014 Castellammare del Golfo (Tp)
2
Southampton Oceanography Centre, Univ. di Southampton (U.K.)
This paper shows the results of the first implementation of a telemetric ultrasonic
system in an artificial reef area (Gulf of Castellammare, NW Sicily). Automated omnidirectional receivers (Vr2; Vemco Ltd.) and miniaturized pingers (V8SC-1L; Vemco
Ltd.) were used (1) to determine the hydrophones detection range and study the
relationship between distance and number of detections (Nd) recorded in a fixed time
interval, and (2) to estimate pinger positioning error throughout the study area,
quantifying the interference effect of single artificial structures.
Throughout 2002, 20 free-water experiments were made holding pingers for 25 minutes
at 45 fixed distances with an unobstructed line-of-sight for signal reception towards the
hydrophones (from 100 to 765 m). Throughout the study site, positioning design and
respective detection ranges of five hydrophones created 17 regions of overlap between
two and five hydrophones and four zones, each unique to one hydrophone. Pingers were
put in fixed positions in the centre of each region of overlap, randomly inside the
artificial reef area or close to (out/inside) a single artificial reef structure.
In the most frequent environmental conditions, detection range of the hydrophones was
about 500 m. Based on free-water relationship between Nd and distance classes,
weighted means of modified Nd were used to localize pingers as a geographic points in
the study area. Pinger positioning error was defined as the distance (in meters) between
the calculated geographic coordinates and the real ones.
Results show a strong negative correlation between positioning error and number of
hydrophones that could detect pinger signals at the same time. In particular, whereas
two or three hydrophones can listen simultaneously, global positioning error is 244 
154 m. Overlap regions with four and five hydrophones cover the artificial reef area,
resulting in a global positioning error of 64  54 m. When the pinger is inside a single
artificial reef structure, the system is unable to localize it (Nd = 0). When the pinger is
close (3 m) to a single structure, positioning error is 130  59 m. However, if the pinger
is at least 15 m away from the structure, positioning error decreases to 54  24 m.
The accuracy of pinger localization inside an artificial reef area, showed in this paper,
represents the first important contribution to know the pinger position by means of a
simple presence/absence telemetric system.