Kongsberg HiPAP User manual

HiPAP®and HPR used in plough
and tow fish tracking
Tow fish tracking
855-164074 / Rev.E / October 2003
Introduction
The HiPAP®system may work down to 4000 meters.
The HPR Super-Short Base Line (SSBL) systems
(HPR 309, HPR 310 and HPR 410) may work down
to 2000 meters using high power, deep-water trans-
ponders. These figures are based on a “normal” noise
level in the surroundings of the vessel and sufficient
source level from the transponder. “Looking” through
the propeller water and having to “look” through the
water column at a slanted angle, will often create limi-
tations to the actual range performance.
In general, the most important factors for getting suc-
cessful positioning results in underwater navigation
are:
• No ray-bending or deflection, due to different tem-
peratures in the water column.
• The best possible Signal-to-Noise ratio (S/N).
• No obstructions or aerated water between the seabed
transponder and the hull mounted transducer.
Ray-bending
Kongsberg Maritime has many
years of experience in handling
these factors. In plough and tow
fish tracking applications, the
point about deflection is unique,
as the positioning will be rela-
tively more horizontal than in
other applications. Please note
that there is no ray-bending effect
when the acoustic signal com-
munication is vertical through the
layers.
The ray-bending effect will start influencing the accu-
racy of the positioning when the angle to the trans-
ponder is 15-20 degrees (relative to vertical), and will
normally increase with increasing angles.
Kongsberg Maritime has developed different solu-
tions to minimize the ray-bending effect.
The HiPAP / HPR system has:
• Functions to calculate the sound deflection through
water, and software to compensate the error caused
by this effect. Both range and angle detection are
compensated.
• Possibilities for taking input from a sound velocity
meter, and a dedicated program will calculate and
display the ray-bending graphically on the display.
An example of operator presentation of the sound
velocity profile of the whole water column, and the
presentation of ray-bending diagram calculated by the
HPR, is presented in the figure below.

The function is not only error correcting, it also gives
the operator a tool to see the limitations of the nature,
as well as it can give the answer to a range problem.
Wrong sound velocity input gives error in absolute
accuracy, but influences very little in relative position
changes and stability.
At some stage, the ray-bending will cause the ray to
deflect upwards (see figure). In such conditions the
interrogation pulse from the transducer will never reach
the seabed transponder, and thereby no positioning can
take place.
An alternative tool for handling the ray-bending effect,
is to use depth sensing transponders, or entering opera-
tor set transponder depth into the HiPAP / HPR system.
Then the system will use this depth instead of calculat-
ing it.
Signal-to-Noise ratio
The next important factor is the Signal-to-Noise ratio
at the receiving transducer onboard the vessel. This is
often the most noisy place, as it is close to propellers
and thrusters. There are two ways of getting the highest
possible Signal-to-Noise ratio:
1. Suppress the noise as much as possible
2. Increase the transponder source level
Kongsberg Maritime extensively uses beam forming
transducers to obtain maximum sensitivity towards the
seabed transponder. This gives less sensitivity towards
the noise sources (thrusters and propellers) and sup-
presses the influence from noise. A sensitivity diagram
of a 30 degree transducer beam is shown in the figure
to the right. As you can see, the horizontal sensitivity
(towards the thrusters) is some 30 decibel (dB) lower
than maximum sensitivity vertically!
• The HiPAP system can steer a narrow beam of only
10 degrees to any direction.
• The HPR 400 series of systems has different trans-
ducers - all with directive beams.
Transponder source level
Kongsberg Maritime manufactures many different
types of transponders. It is always important to select
the right transponder for the specific application.
Transponders vary in size, battery lifetime, transmitter
source level and beam pattern. If success is difficult in
for example a noisy environment, you should always
see to that you have a transponder with high source
level to obtain the best Signal-to-Noise ratio. These
transponders are often large due to narrow beamwith
which concentrates the energy in the right direction.
A high power transponder typically has a source level
of 205 dB. A transponder rated for less than 1000 meter
typically has 190 dB. A high power transponder has
approximately 32 times higher source level.
To handle possible noise problems on a plough / tow
fish we suggest to use a responder instead of a trans-
ponder. The responder is triggered and controlled from
the onboard HiPAP / HPR system through an umbili-
cal.
Aerated water
The hull units are designed to allow the transducer to
work some 3,5 meters below the hull. The main reason
to have the transducer at this depth is to get the trans-
ducer down below the “natural” aerated waters sur-
rounding the hull.
The transducer location in the hull is also important.
Kongsberg Maritime will assist to recommend this
location, based on a General Arrangement drawing
showing the entire hull with all propellers and thrust-
ers.
If a Dynamic Positioning (DP) system controls the
engines, it is important that any azimuth thrusters have
“abandoned zones”, to avoid water flushing towards
the transducer(s).
Strandpromenaden 50
P. O . B o x 1 1 1
N-3191 Horten,
Norway
KongsbergMaritimeAS
Telephone: [phone]
Telefax: [phone]
E-mail: [email protected]
www.kongsberg.com