This presentation will explain what is different and new about the ECHOES products and introduce a new approach to Sub-Bottom Profiler (SBP) data acquisition and processing which has the potential to make a real difference to workflow.
Quick intro abaout IXSEA product and then focus on ECHOES and DELPH as associated products This presentation will explain what is different and new about the Echoes products and introduce a new approach to SBP data processing which has the potential to make a real difference to workflow.
First lets look at what we are trying to achieve with Sub bottom profiling. These two images are shot over the same area with two different SBP systems, the image on the left is a high resolution system, whilst the image on the right is lower resolution but has better penetration. The images are an example of the typical trade off required when picking which SBP system to use. In an ideal world we would have the resolution of the image on the left with the penetration of the image on the right. In the real world we have to make a choice, if we are lucky we can use multiple systems.
The Echoes products cover the whole range of frequencies and powers typically used offshore. The product of most interest to me when I found out about it was the Echoes 1500, This is a low frequency wide band chirp system operating at up to 9kW This is extremely high power and covers a frequency band ranging from 650Hz to 2500Hz, a massive bandwidth at these frequencies. The Echoes 3500 is a hull mount pinger alternative with high power and good beam width, the wide band capability improving on the resolution however. The 5000 has at least the resolution and penetration of the best surface tow boomer The 10000 is an extremely high frequency system more suited to shallow water ports and harbours type work where absolute maximum resolution in soft sediments is required.
OK, so what makes the Echoes products special, The key point is with the transducer technology, Echoes transducers are specially designed for very wide band operations. They start with a basic Tonpliz design, but specially modified to produce a wide band response. As described on the slide, a Tonpliz transducer consists of a stack of ceramic rings squeezed between a heavy tail mass and a head mass, when the ceramics are electrically excited they expand and contract to cause movement of the head mass and therefore inducing pressure waves in the surrounding fluid.
In the Echoes 1500 product we have a single large Janus Hemholtz transducer, the Echoes 5000 uses three different Janus Hemholtz transducers to get even wider bandwidth. A Hemholtz transducer consists of two Tonpliz transducers stacked back to back within a hollow tube. The hollow tube has a gap in it allowing fluid to enter. When the head masses expand and contract the volume inside the tube also changes forcing water to flow in and out of the tube. Water has mass, and therefore inertia so when the tube stops expanding the water continues to flow in to the cavity for some time. The same happens when the cavity stops contracting. The overall effect here is to induce Hemholtz resonance in the cavity which typically peaks at a lower frequency than the Tonpliz transducers could. The overall effect is a widening of the bandwidth of the transducer.
A typical boomer system running at very low energy settings is able to achieve a pulse width as low as 120 ”s. If we assume a velocity of 1450m/s this equates to a resolution of 17cm. In actual fact power is rarely set this low, and increasing the power increases the pulse width so typical operational resolutions are more likely to be in the order of 25cm
Bandwidth is the key of good SBP, Increasing the bandwidth is a goal to improve resolution. Three tuned transducers are used to increase the bandwidth,
Resolution and power considerations are only one part of the story. Stability of the system in relation to the seabed, and ambient noise levels also have a huge impact on the quality of the final data. If the platform containing the SBP system is moving around a great deal the produced data may be unusable. Typical examples here are surface towed systems. These systems can be excellent in the right conditions, and even a large swell does not rule out their operation as we can use a sell or heave filter to eliminate the effects. What really impacts the data quality is quick unpredictable motion such as caused by âchopâ or small waves which swell filters tend to struggle with. By towing a system âDeepâ and here I don't mean Full ocean depth, just deep enough to get away from the sea surface effects and noise from the towing vessel we can maximise our chances of obtaining the best possible data. Of course given enough resources we would like to have our SBP systems very close to the seabed in order to minimise beam spreading and to get the absolutely most stable and quiet environment. However here we hit another of the trade-offs we tend to get used to with SBP systems. When towing close to the seabed it is difficult to get the power we need to the SBP system, cables become large and expensive and handling systems have to grow in proportion. This is why the Echoes 1500 is configured for towing at up to 300m even though the transducer is capable of much much deeper operation.
On the left we see the typical processing flow for SBP or SSS data. Data is gathered by the sonar operators, passed to a geophysicist to confirm the quality is OK, then either offshore, but more normally onshore it enters a completely different processing and interpretation phase. The Delph approach to software is to provide the right job. The acquisition phase is all about getting the data recorded whilst checking the basic quality of the data. For this we provide a simple small acquisition package that is tuned specifically for this operation. If a function is not absolutely necessary for ensuring the data is of high quality and stored safely then it is not included in the acquisition packaged. Typically in the offshore environment, SBP and Sonar acquisition systems are vastly under utilised. Operators of acquisition systems are there to ensure the acquired data is complete and of good quality. There is a great temptation to an operator of an acquisition system to take a profiling system that is producing dubious quality data and apply a huge array of processing tools to the data during acquisition In this way, data that has obvious flaws is made to look acceptable, with the assumption that further processing will improve it even more. In reality there is no possible improvement because all the processing tools have already been used to their maximum. By limiting the tools available in acquisition to gain control and band pass filtering sub optimal data is quickly identified changes to the data quality during a job can be noted easily
Here we see the range of DEPH SBP tools and how they correlate with the typical data flow. Explain.
Typical SBP or SSS processing software takes a scrolling waterfall display approach to processing. Changes are made on a ping by ping approach and the data played back in the same manner as in acquisition Changes to the processing parameters are only applied from the time the change is made rather than for the line as a whole. If the operator makes a change to the gain settings for example he / she has to rewind the data to the beginning of the file and start replaying the data again. Because the delph processing software does not use a waterfall display, but instead treats the data as an image (as far ad the user is concerned) it means processing can be applied to the whole line or section of line as the user wishes, without having to go back to the start and âreplayâ the data. Modern advances in computing technology mean it is no problem to keep the entire line in memory and the old view of replaying the data from tape is now obsolete Processing applied to data in memory is vastly faster than reading in data from disk and applying processing on a ping by ping basis.
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