Sub bottom profiler

Geophysical applications on environmental investigation, mineral prospecting, engineering, archaeology, forensics, hydrology...
Hutch
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Re: Sub bottom profiler

Post by Hutch »

I just bought a stratabox last week and have not had much luck if anyone is interested in processing data please advise.

timver
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Re: Sub bottom profiler

Post by timver »

If you want to do some fancy data processing, just forget about it. The data you saw on your screen during the data acquisition is pretty much what you can get.

sonarman
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Re: Sub bottom profiler

Post by sonarman »

To Hutch:

If you want to process strataBox data you can contact me....or any one else whom works at Syqwest Inc....

rtarini@aol.com

508 944 5805...I am happy to work with any customer directly....

PS- To all those whom would care to know here is another customer whom is happy to provide a reference as to how well the product works and how we support our customers....

"Dear Mr. Tarini,

I am extremely grateful for the support Syqwest Inc.has provided. Global One Survey LLC. will be sending a detailed letter directed to your company depicting in detail the extent of your tech support and professionalism. I must say that the Force Main pipe was not located by some of the best tow fish in the market (Edge Tech) and these were on board my boat with personnel that operate these for many years as well as having worked for the Navy providing this and other technology for 29 years.The Strata Box worked in a rough environment were current,traffic and inclement weather play a big role.

P.S. I know you made it happen but please send my gratitude to Russ and Andrew for continuous support and respect.
Sincerely"

Jose M. Rives., PSM,CEO
Global One Survey
39 N BlackWater Ln.
Key Largo Fl. 33037

azgeoguy
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Re: Sub bottom profiler

Post by azgeoguy »

timver wrote:Correct me if I am wrong:

When you try to use deeper depth settings (longer trace), the instrument will automatically use lower sampling frequency, because it can only store about 400 (?, don’t remember exactly) samples for each trace. As a consequence, even you can use the zoom window, you can not get the best resolution you could get (about 6cm as they claimed) for the whole length of the trace, no matter how ideal the water or the sub bottom conditions are. I was caught in surprise since it’s against common sense. I can’t say they are lying, but it’s misleading when they say “6cm resolution with up to 40 meters bottom penetration”. You can never get both at the same time.
I'm new here so I hope this comes across okay. I have around 14 years doing geophysics, and 20 doing geology.

It is important to remember that a trade-off in depth of resolution versus depth of evaluation always exists in any data collection/processing scheme. This trade-off is a problem intrinsic to the whole process, and is in fact a quantitatively definable problem that an entire industry of filtering and processing schemes tries to address. We practitioners should always be extra wary of any manufacturers who appear to, either through ignorance or willful intention, ignore this basic fact when they claim full resolution at full depth of the instrumentation. (Note that I am not specifically referring to any of the manufacturers in this post, it's just a good general practical principle). It reminds me of my favorite quote from Einstein:

"As far as the laws of mathematics refer to reality, they are not certain; and as far as they are certain, they do not refer to reality." Albert Einstein, "Geometry and Experience", January 27, 1921

We must always recall that we are creating models of the problem based oftentimes on our interpretation of inaccurate, insufficient and inconsistent data. Reducing your uncertainty so that your model comes close to approximating reality should always be our goal, but there will be no perfect solution that entirely removes the inherent trade-off. Geophysical problems are often overdetermined, and underconstrained, often leading to any several of models that might fit your data. You just have to be aware of it, and manage your data collection, processing, and field techniques appropriately along with any supplemental information from other sources such as borings, well logs, soundings, etc...to enhance the chance that your final approximation or model will be of some practical use.

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geophix
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Re: Sub bottom profiler

Post by geophix »

azgeoguy, well said. Also, if you are not familiar with a instrument, It's good practice to rent it before you decide to buy it.

rolfaalto
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Re: Sub bottom profiler

Post by rolfaalto »

Has anyone used a Stratabox (or similar) in a river environment?

I am planning several field campaigns to Papua New Guinea and Bolivia, where we are studying various aspects of fluvial geomorphology and biogeochemical fluxes for these large tropical river systems. I have worked extensively in both locations before, but don't have much experience with sub bottom profiling (just ADCP work). So, I'm looking for a simple/cheap system that can be run off a small boat (eg., hang over the side) and off a maine battery for all-day usage. We are also doing a lot of driling to ~30m depth, so will have some comparisons between what is profiled and what we bring up with the drill. We'd like to image between 30 and 100m into the sediment.

The water depths are typically 5-10m and the underlying material is mostly river deposits (sandy point bar deposits, silty floodplains, clayey oxbow lake plugs), with some bedrock spurs. No waves, and we can drift with the current at 1-2m/s so probably no problem with that.

Any advice on the applicability of Stratabox or other products that I could consider?

Cheers,

Rolf Aalto

gmowoe
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Re: Sub bottom profiler

Post by gmowoe »

I am not an expert, but it looks like a chirp system is the best option for you.

Gery
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Re: Sub bottom profiler

Post by Gery »

As gmowoe, I think the same, you need a chirp system. According to your explanation, I would suggest the X-Star or 512i from EdgeTech, it is quite good for this kind of environment, but expensive though (liks US$ 82000). You ask for lease to this company as well. Stratabox... it might work, I've never used in a river. However, in your case I would spent money in an edgetech system. Check out the attached picture, I think you need this type of results from your survey (e.g. vertical/horizontal resolution, broad spectrum, well tie, etc).
Attachments
Boomer-vs-chirp comparison
Boomer-vs-chirp comparison

gmowoe
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Re: Sub bottom profiler

Post by gmowoe »

I guess the lower one is from X-Star? Amazing. It looks much better in both resolution and penetration than the image from the Boomer system.

kaden
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Re: Sub bottom profiler

Post by kaden »

X-Star is used by many companies. It's much heavier than Stratabox. The good news is that you don't need to carry it all the time. :)

rolfaalto
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Re: Sub bottom profiler

Post by rolfaalto »

Thanks everyone for your detailed responses and other information.

I have found some supporting papers from work on the Mississippi plus many comments from University colleagues who have done extensive surveys there with Edgetech systems. It does sound like CHIRP would be better in all ways, but it seems that for either approach there is a problem because of the massive coarse sand lenses that are found in most rivers -- at even at its lowest frequency, the systems have trouble penetrating much below a meter into the active sand layer. They have generally associated this problem with acoustic absorption by the sand. Therefore, the data are essentially rendered a 2-D profile of the sediment-water interface (from Edgetech 216 units).

The best results have been from a much larger Edgetech 512 system at 0.5 Khz, but penetration there is still a major problem if sands are > 5-10m thick with the best-case published examples being rather dissappointing. However, this system is far too massive and expensive for our available boats and budget. The rental/shipping costs for a single 45-day campaign an Edgetech system to Papua New Guinea or Bolivia are going to run me > $10k -- most of which time it will spend in the crate not being used (rentals are a very poor cost/benefit ratio for people like me who work in remote areas with weeks of shipping time on either side).

So, I suppose that I am now looking for the best compromise that might SOMETIMES provide useful penetration/data for these large rivers -- again, we are there to accomplish a large number of scientific objectives, so the sonar survey is something of an add-on that is intended to provide added value at low time costs/hassle while we are otherwise trolling around for other reasons. We do need hydrographic data for some numerical models of the river systems we are calibrating, so why not also try to get subsurface data at the same time? Our budget for this needs to be < $30k.

As such, I am now thinking about either the Stratabox 3510 unit (dual frequency 3.5/10 Khz) or their still reasonably priced B2010PC unit -- a small/inexpensive CHIRP that outputs 4Kw at 3.5-200KHz. This appears to be ~10x the power of the first unit (better penetration) and CHIRP should give better images.

Any additional thoughts/information would be very much welcome!

Rolf Aalto
Associate Professor
Unversity of Exeter/University of Washington

Gery
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Re: Sub bottom profiler

Post by Gery »

Hi Rolf,

Uhmm, just some thoughts about your explanation... I've processed recently Stratabox 3510 data from the southern channels of Chile (3.5 kHz, 4-transducer array, 1000 W), this environment is not a river environment though, but several coarse (sand and gravel) layers, as well as fining-up sequences were found above the 100 meters water depth. Below this depth, thin bedding patterns were found (up to 60 m penetration at 400 m water depth). With this system, I found that the former are characterized by transmission loss and the latter by a quite-transparent seismic character. The bandwith in general was about 1000 Hz. The vertical resolution varies between 1 to 2 meters. However, close to the shoreline were sampling coring were done, a mix of coarse sediments were retrieved and a very poor seismic character was acquired. In literature (eg. Cobo et al 2002), you find that this is because the shape of the pulse signal emitted (at least for a 1-element transducer, 10 kHz). So, I think, you will find this system useful in defining coarse layers and deducing thin bedding sequences, however, if you want to tie small-scale features (eg. laminae) from corers and do thin-bedding analysis, you will need a chirp. You could search in Konsberg and Knudsen, perhaps they are cheaper than Edgetech.

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geophix
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Re: Sub bottom profiler

Post by geophix »

Apparently a chirp system is a better choice if your budget allows. If you don't use the best one you can get, you may keep wondering what you might have missed during the surveys. ;) Here is the link containing a list of sub bottom profiler manufactures including SyQuest, hope it helps:
viewtopic.php?f=2&t=316

rolfaalto
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Re: Sub bottom profiler

Post by rolfaalto »

Thanks for the information.

I have been told by a SyQuest tech that there are some considerations about minimum depth that will limit the frequency that I can use. For example, the 3.5kHz frequency will not work well in less than ~9m of water -- I am not entirely clear on the formula for this or the likely degradation of the signal, but it sounds like a problem for me because only the deeper parts of my river channels reach that depth or more. So, I'm now thinking about the 3.5kHz frequency as a secondary option and seeing something like this 2000 Watt 12 kHz tranducer as my primary ducer:

http://www.syqwestinc.com/transducers/T ... ochure.pdf

An added advantage of ths transducer is the 18 degree beamwidth, which should both focus the power and give me a better map for hydrography.

Could somebody please clarify the minimum depth considerations for various lower frequencies? I certainly would like to consider the 3.5kHz unit as it provides superior ability to penetrate coarser material (eg., fine sand), but perhaps I am limited by depth?

Thanks,

Rolf

kaden
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Re: Sub bottom profiler

Post by kaden »

For a pinger or chirp system, the maximum sub bottom penetration depth is often limited by the water depth because of multiple reflections, i.e., in 5m of water, the maximum sub bottom penetration is about 5m. There might be computer programs dealing with this multiple reflection problem, but I have not seen any real examples.

gmowoe
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Re: Sub bottom profiler

Post by gmowoe »

rolfaalto wrote:I have been told by a SyQuest tech that there are some considerations about minimum depth that will limit the frequency that I can use. For example, the 3.5kHz frequency will not work well in less than ~9m of water -
The sound wave velocity is about 1500m/s, if the frequency is 3.5KHz, the wavelength is about 1500/3500=0.43m. It's much less than 9m. I guess the source wavelet must contain many cycles, making it hard to differentiate the reflections from the direct arrival.

For the chirp signal, the typical duration of the source wavelet is about 0.02s. The wave length would be 1500*0.02=30m. I don't know exactly how to compare this number with the minimal water depth required since chirp signals have special data processing techniques.

Gery
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Re: Sub bottom profiler

Post by Gery »

It's not recommened working below 10-m water depth, however, I think you could survey up to 5-m water depth but your data will have a quite poor S/N ratio. You have to be aware that seismic reflection is intended to delineate the subseafloor geometry, but based on the S/N ratio and impedance variation, you may infer its sedimentary nature. At this depth, you will have to deal with the multiple, as Kaden pointed out.

I wouldn't expect a 0.43-m wavelenght for the syqwest system, the output bandwith of 3.5 kHz is nominal, so far I haven't seen data like that coming from this system. The direct arrival occurs when the transmitter and receiver are separated, like sparkers and boomer (or mcs systems), or perhaps someone else could provide details on this for scs pingers like stratabox.

The 12-kHz transducer might work, I've seen some examples with poor-to-good results, but it's a high-frequency source, so you'll have problems in coarse sediments and your penetration will be restricted (your bandwith will be poor). Yes, the 18º beamwith is good, however, your directivity will increase with more transducers.

Rolf, the multiple below the 10-m water depth will certainly affect the quality of your data, for all systems, it's a physic phenomenon. There are some tricks to attenuate them during the survey and in post-processing though, but it will degrade part of your data ouput.

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geophix
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Re: Sub bottom profiler

Post by geophix »

Innomar Technologie's parametric sub-bottom profiler is very good for shallow water environment, mainly due to its short pulse without the ringing effect. But it could be prohibitively expensive.

Gery
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Re: Sub bottom profiler

Post by Gery »

Yes, Geophix is right, I've seen pretty good data coming from that system, good S/N data coming from 2-m water depth. But it's a parametric system, big bucks.

kaden
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Re: Sub bottom profiler

Post by kaden »

The transducers of parametric sub bottom profilers are actually much smaller than those of chirp systems with comparable low frequencies. So parametric sub bottom profilers are more suitable for smaller vessels or boats.

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Re: Sub bottom profiler

Post by marken »

For the chirp signal, the typical duration of the source wavelet is about 0.02s. The wave length would be 1500*0.02=30m. I don't know exactly how to compare this number with the minimal water depth required since chirp signals have special data processing techniques.
if the water depth is too shallow,the initial reflections will arrive when the receiver is still saturated by the direct arrival (with separate transmitter) or the receiver has not been ready yet if it's also used as the transmitter. So the data is going be messed up, at least for the top layers, no matter whether you have special data processing techniques or not.

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Re: Sub bottom profiler

Post by Hutch »

Sub bottom profiler like new includes everything $$$$$ 4500.00 Hurry
Last edited by Hutch on Wed Oct 13, 2010 12:43 pm, edited 1 time in total.

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Re: Sub bottom profiler

Post by jenjen »

I would like to know why CHIRPs dont work well in coarse sand and gravel, you said it because of the shape of the pulse signal emitted but can you expand??
or point me in the direction of papers which explain this??
thanks!!

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Re: Sub bottom profiler

Post by gmowoe »

Coarse sand and gravel are not good for all sub bottom profilers, not only for chirp systems. The seismic energy dissipates in them instead of traveling through. So more powerful the energy source is, the stronger the signals will be. Compared to pinger and chirp systems, boomers and sparkers are much more powerful, and the waves they generated contain lower frequency signlas which also helps.

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Re: Sub bottom profiler

Post by jenjen »

So is it the large partial size in the sand/gravel that dissipates energy more effectively than small partial size of silt?? Or is it that there is more space between the partials in sand/gravel which prevents the wave travelling through?

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