Top 10

The MAC, technicians, and colleagues encounter several common factors that limit data quality across a wide variety of platforms.



= Top 10 common issues =

In no particular order, here are ten common complications to consider when planning, collecting, and processing multibeam data:


 * 1) Inaccurate vessel offsets (or incorrect interpretation)
 * 2) Data quality depends fundamentally on sensor configuration; see Dimensional Control
 * 3) Inadequate sound speed profiling and/or mismatches at the transducer
 * 4) See Sound Speed and SmartMap
 * 5) Higher noise levels due to biofouling and changes in machinery
 * 6) Run pre- and post-shipyard RX Noise tests to examine this
 * 7) For Kongsberg systems, see the Transducer Cleaning, Fairing, and Painting Procedure
 * 8) Inappropriate runtime parameters
 * 9) Automatic modes still need monitoring
 * 10) The depth gates mean business!
 * 11) Infrequent calibrations
 * 12) Routine calibration (patch testing)  can rule out some biases
 * 13) Interference from other acoustic or electronic systems
 * 14) Is that 12 kHz bridge fathometer really secured?
 * 15) Synchronize your scientific echosounders
 * 16) Sea state, aeration, and bubble sweep along the hull
 * 17) Work is underway to adjust ping cycles around washdown events
 * 18) Meanwhile, testing RX Noise vs. swell direction can help to identify quieter/better survey orientations for each particular vessel
 * 19) Mapping is often the 'back up plan' when other work is on hold due to sea state!
 * 20) Waterline errors
 * 21) Like other sensor offsets, this directly affects the reported depth
 * 22) Waterline impacts refraction correction by changing the 'starting point' in the sound speed profile
 * 23) The value depends on the manufacturer's conventions and is not always equivalent to the draft
 * 24) Sound Speed Manager plots the transducer sound speed value and depth; this can be extremely helpful in verifying the waterline configuration
 * 25) Infrequent operation
 * 26) It takes longer to identify issues when the systems are not operated routinely
 * 27) When issues do arise, they are under more 'critical' circumstances and become 'emergencies'
 * 28) Opportunistic testing and transit mapping helps to maintain operator familiarity and catch problems early
 * 29) Outdated software and firmware
 * 30) Over the 10+ year hardware lifespan, manufacturers routinely release software and firmware updates to fix real issues with operation
 * 31) While some of these might be simple user interface updates, some address fundamental errors in TX or RX processes
 * 32) Keeping systems up to date can improve data quality (e.g., reduce outliers, provide new warnings to users) and protect hardware health (e.g., adjust duty cycles or power limits)

= Uncommon multibeam issues =

Here are a few examples of issues that severely impacted data quality and took a while to sort out, partially because they may are not common problems.


 * 1) Transducer anti-fouling paint (over-application)
 * 2) If an array is painted, it must follow the manufacturer spec
 * 3) Adding mass (paint) to the transducer can drastically change its frequency response
 * 4) This reduces TX power and RX sensitivity, while increasing acoustic attenuation
 * 5) The net results are very poor coverage and accuracy for the incorrectly painted arrays
 * 6) Array orientation in sensor setup (incorrect rotation)
 * 7) Some systems allow 180-deg rotations of the arrays to fit various configurations
 * 8) Incorrect 'rotation' in the sensor configuration (i.e., array heading) can be applied at the flick of a toggle button
 * 9) Incorrect 'rotation' of either array can lead to fundamental mismatches between the pulse forms transmitted at ping time and expected during the RX cycle
 * 10) The net results are wildly inaccurate soundings (or no bottom detections at all)
 * 11) These symptoms are often less severe with CW sectors and extremely severe where FM is used (a telltale sign of incorrect array rotation!)
 * 12) Array installations must be documented with pictures showing the cable orientations (and module numbers) to confirm setup in the software
 * 13) Array module order (cabling out of sequence)
 * 14) Some arrays are made of multiple modules which must be installed in a particular order
 * 15) Installing or cabling the modules out of order leads to fundamental beamforming errors (TX, RX, or both!)
 * 16) When TX modules are cabled out of order, there is a risk of the radiated TX beampattern deviating severely from the intended shape and amplitude
 * 17) The net results are poor bottom detection, scattered distributions of soundings, and mistracking
 * 18) Mistracking is sometimes more clearly evident on slopes, where TX sidelobes ahead or behind the main lobe are providing stronger returns