Interferometric Sounder Hydrographic Survey Launch AEH 174 Macha FS 20 NAVOCEANO 2004 July

Summary AEH 174 Peruvian Hydrographic Launch Interferometric sounder Projects related

Peruvian Hydrohraphic Launch AEH 174 “MACHA” ATLAS FANSWEEP 20

Peruvian Hydrographic Launch

ATLAS FANSWEEP-20 100 KHz Máx. range 600 mts. Coverage 12 times the vertical depth 1440 beams per swath Fore and aft angle 1,3° Stabilization of roll, pitch, heave Precision de ± 0,10 cm + 0,2 % of the depth

Depth Range - Coverage

To establish parallel tracks each other , arranging of spacing OHI (SP-44)

Multibeam System Specs EM 3000 vs. Fansweep 20   Frequency (kHz) 300 200 Transducer single dual or dual 35*35cm Configuration Flat T Flat Source Level 215 227 Power (kW) 0.6 2*1 Pulse length (ms) 0.15 0.04 Beamwidth (deg) 130*1.5 180*1.2 1.5*30 Number of beams 127 20-1440 Beam spacing (deg) 0.9 Max ping rate (1/s) 25 12 Angular Coverage 130 160 Swath Width 4.3xWD 11.3xWD Along Track BW 1.5 1.2

Cost Estimates Hydrographic Launch AEH 174 MACHA with Fansweep 20   Personnel 6 person crew Salary $ 50 $ 1,200 1 Vessel 4 days Leasing ~$2000 $ 8,000 Fuel ~400 gallon/day Per Gal $3 $ 4,800 1 Fansweep 20 Leasing ~$9000 $36,000 Total: $50,000

Systems Conventional systems to date use either the principle of beamforming, sometimes combined with phase measurement, or the interferometric phase measurement principle. The basis for both methods is a signal processing procedure which measures sound travelling times and transmitting or receiving angles relative to a hydroacoustic transducer and determines from these the depth and position of a point being measured on the bottom, doing so relative to the normal to the transducer. Both conventional methods have their special characteristics.

Sample detected Sunk Boat 20 Noviembre 2001 Latitud 12° 03.72’ Longitud 77° 09.50’

Sampled detected Latitud 12° 03.72’ Longitud 77° 09.50’

Disadvantages of interferometric sounder; Typically slower along-track ping rate (pings port - listens, then pings starboard), making it difficult to achieve IHO target detection requirements (by bathymetric means) at normal survey speeds. From our experience, interferometric systems do not detect the seabed as robustly as beam forming systems (i.e. more noise and higher standard deviation). From our experience, interferometric systems are not as good at detecting structures rising steeply from the seabed (i.e. dock walls, sand waves, some rocks).  This is due to an apparent inability to resolve two echoes arriving at the same time from different directions within the same beam.  Some modern systems claim to get around this. With beamforming systems, it is easier to steer and compensate for vessel motion.

Advantages of interferometric sounder: Good pseudo sidescan (usually better that beamforming backscatter) this can assist target detection Good across-track sounding density (but not in nadir) Wider swath widths (if high along-track ping rate not required) Typically cheaper than beamforming systems

Project - Survey Specifications Planning Specifications Specifications greater due to several external factors Water level Heave Water column stability

Surveys on Rivers Peru has more than 20 rivers able to be navigate, they have an around extension of 16000 Km. So far ,more than half of them have been surveyed ,with Single beam echosounder onto the thalweg channel. The Peruviam Hydrographic Office has the goal to acquire a Multibeam Echosounder for Riverine Surveys.

Concerns The main issue with the Fansweep is the poor ratio between data acquisition and data processing.  The processing software supplied by Atlas was slow and manually intensive.  There have also been some obstacles due to hardware problems over the years. Input from Atlas seemed to be required, as the setups were not totally transparent.  For example, there were some complex calibration procedures and the help menu is not available.  It is worth remembering however that the DHN procurement began in 2001, so things may have improved in recent times. It is also worth remembering that the number of beams in a beamforming system is not comparable to the number of datapoints in an interferometric system (the system is just resampling), so we should be cautious about the sales pitch "more soundings".

Interferometric Sounder Hydrographic Survey Launch AEH 174 Macha FS 20