NAVICO 3D SONAR

[jimh]

NAVICO recently announced the introduction of a "3D" SONAR. The SONAR does not actually capture three-dimensional images. It does have the ability to acquire the usual pseudo-two-dimensional side-scan SONAR images, store them, then recall historical two-dimensional image planes or slices, and assemble them graphically in a manner that gives to the user a very appealing representation of the bottom contour and echo locations on a two-dimensional conventional LCD screen. The device also appears to offer sophisticated manipulation of these views.

Describing this device in words is cumbrous. The device can be viewed in operation in this recorded presentation:

https://www.youtube.com/watch?v=pI0lV20xL9I

The presenter in the above recording does make a few inferences that exceed the actual capabilities, but the images on the Navico SONAR screen speak for themselves. The most remarkable aspect of the recording is the extremely uneven sea bottom over which it was made. The bottom is quite irregular and makes for a perfect demonstration.

The 3D SONAR is implemented by specialized hardware. The components supplied with the StructureScan 3D Module are:

--a specialized dual transducer, which is quite large compared to the familiar skimmer transducer often used on small boats and has a dual connector cable;

--a similarly large metal mounting for attachment of the transducer to the boat transom;

--the Structure Scan 3D module, with connections for the dual transducers, and three Ethernet connectors;

--a power cable; and

--a Navico-type Ethernet cable.

The transducer connects directly to the StructureScan 3D module. The module connects to a display using the Ethernet cable. One presumes the sophisticated processing and graphics manipulation are done in the module, with the associated display providing the user controls. The Structure Scan 3D module only works with the latest-generation Navico devices, the Lowrance HDS-series Gen3 devices or the Simrad NSS evo² or NSO evo² devices. In addition to the remarkable ability to manipulate the graphical images of the sonograms, the device also appears to have enhanced performance as a side-scan SONAR, with excellent range and very good resolution.

For more information see

http://www.simrad-yachting.com/en-US/Pr ... en-us.aspx

and

http://www.lowrance.com/en-US/Products/ ... an-3D.aspx

This product was announced some time ago, but production units are now apparently just arriving to dealers and getting to customers. The retail price is $1,000. Of all the SONAR enhancements recently brought to the marketplace, this device is certainly among the most interesting.

[jimh]

Although the Simrad StructureScan 3D module is impressive, I do not believe that it can combine the data from multiple passes over the same sea bottom into a composite representation. A few years ago there was a software product available from a small software developer (DrDepth) that would ingest raw SONAR logging data and turn the echo-sounding into a three-dimensional representation or mapping of the sea bottom. Of course, this was a post-processor, and you did not get the composite mapping in real time. You'd make many passes and many recordings, then input all the data to the software for processing. The software would output a mapping with a 3-D presentation. This software company was bought out by Johnson Outdoors, the parent of Humminbird. More on this at

http://continuouswave.com/ubb/Forum6/HTML/003416.html

[jimh]

Recent comments in PANBO.COM suggest that the Navico 3D SONAR is using interferometry. NOAA has an interesting explanation of the method of interferometric SONAR, also known as Phase Differencing Bathymetric Sonar. In this technique, each ping is evaluated by multiple sensors many times per second, and the resulting 3D imaging is a composite of a great deal of mathematical manipulation of the returning SONAR echo data. See

http://www.nauticalcharts.noaa.gov/csdl/PDBS.html

for more information on the technique.

[jimh]

There was a curious coincidence in the use of the terms "chirp" and "interferometry" in the news recently, when much fanfare was given to the detection of gravity-waves by scientists at LIGO, the Laser Interferometer Gravity-wave Observatory. Evidence of the gravity-wave detected by the interferometer was released as an audio recording whose sound was described as a chirp. I thought this a curious coincidence because recreational boaters are presently being sold fish-finding products whose functionality is described with these same terms, chirp and interferometric.

The term chirp as used in connection with the gravity-wave detector is used as a description of the nature of the sound of the signal detected. This actually is the same usage as the original use of the term chirp in connection with frequency-modulated/pulse-compression-demodulated SONAR, that is, to refer to the acoustic sound of the signal. Somehow the makers of recreational SONAR products using frequency-modulated/pulse-compression-demodulated techniques decided that chirp was a better term, but they turned chirp (the word) into CHIRP, the acronym, and invented a new meaning to fit the letters which unfortunately makes little sense but has come to be remembered by many boaters.

Lowrance themselves has not yet introduced the terms interferometer, interferometric, or interferometry into their marketing jargon for the "3D' SONAR, but it is believed that the underlying technology of the device is based on those methods. Apparently that is how the Navico folks explained it to the boating writers, for example, to Ben Ellison (of PANBO.COM) who used the term in his blog post about the product. Ben's blog is being widely quoted, and it will likely become the source for linking interferometry to the Lowrance 3D SONAR. Lowrance likes to keep things simpler, so they'll probably keep calling their SONAR with the term "3D", as interferometric is probably not going to sell too much product to recreational anglers of certain fish species.