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Aug 04 2011

Hydro Survey: Multi-beam vs. Single Beam (Part 2)

Given what I mentioned in Part 1: the density of data, the minimal post-processing (and time savings), and the beautiful mapping results, why would I ever use a single beam depth sounder for a hydrographic survey? There are 3 areas where I think single beam depth sounders still win: cost, data deluge, and surveying in shallow water.

Cost: Multi-beam is Significantly Higher

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The cost of a multi-beam system is still significantly higher than single beam, typically $10,000 versus $200,000. A multi-beam system will have 2 GPS receivers, pitch and roll sensors, and the operator will need much more training. The cost is coming down gradually but so are single beam depth sounders. There are systems offered by Seafloor Systems, and Reson’s “entry level multi-beam system” HydroBat, that are closer to $100,000. However, that cost doesn’t take into account the proper boat you need or the training needed.

Data Deluge: Single Beam is Still Easy to Handle

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The difference in the amount of data collected between multi-beam systems and single beam systems is not merely an advantage for multi-beam but also a disadvantage. Do you have a system that can handle the loads of extra data? More importantly, does your client? This is the same problem I’ve been running into with LiDAR. It’s a lot of excellent data but my computer and software struggles to handle the point cloud or LAS data. The only way for me to view the data is to process it down to basic contours or a generalized TIN. Global Mapper can handle that level of data well but it’s typically not the end software. LizardTech now has MrSID 4 but we’re not quite there yet (unless you want everyone to have software packages costing upwards of $50,000). This is a major problem that software and hardware companies recognize but it will take time for the ability to handle the data deluge to trickle down to most of us and especially most of your clients. Part of this problem is not just the amount of data but the shift from 2D to 3D.

Shallow Riverine Reaches: Single Beam Still Rules

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Multi-beam is not ideal for work in shallower riverine areas but was made, just as single beam systems typically were, for ocean and coastal surveys. It works magnificently with depths over 100 feet built into large vessels but try using a multi-beam system on areas with depths ranging from 1 – 10 feet. The lower the depth, the more you start to lose the efficiency and use. Also, what about more inaccessible areas?

The Verdict: Use the Right Tool for Right Job

The reality is that given the current cost, amount of data, and the shallow water limitations of multi-beam systems, single beam systems will still be around awhile. Bathymetric LiDAR may try to move in on single beam surveys as well but turbulence and sediment laden systems will likely always be a hindrance to it.

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  1. Hydro Survey: Multi-beam vs. Single Beam (Part 1) » Hydraulically Inclined

    […] Hydro Survey: Multi-beam vs. Single Beam (Part 2) » […]

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