Gundalf: Marine Seismic Airgun Modelling Software Package
Gundalf is a state of the art Windows or Linux-based airgun source modelling software package based on many years of research. Airgun array computer modelling is an enormously cost-effective exercise given the cost of downtime of a seismic survey vessel for signature tests or concerns about the effects of drop-out. In the processing centre, simple knowledge of the acquisition geometry and gun types allows an accurate signature to be generated for sophisticated signature deconvolution.
It has taken a number of years to refine understanding of the physics of airgun bubble interaction to its current level but it now offers a genuine alternative to the very costly experimental approach or the uncertainties inherent in near-field extrapolation.
Gundalf™ is capable of modelling source arrays of up to 128 guns for all modern gun types including the very latest Bolt eSource™, with full interaction allowed between them. Linear superposition of sub-arrays or even individual guns as has often been used, is rejected in favour of full physical modelling. No scientific compromise is made here, the physics at the heart of Gundalf™ is capable of modelling the phase locking observed in closely-interacting airguns right down to the edge of the super-foam region. It contains arguably the most advanced physics of its kind anywhere.
Gundalf™ is rigorously calibrated against large datasets of signatures recorded in specialist facilities.
The system is available in two forms, Designer and Optimiser, both of which use the same state of the art physical modelling engine.
- Enables the geophysicist to model the signature of up to 128 fully interacting airguns in an array quickly and accurately.
- Includes all modern gun types including Bolt eSource and Long Life, Sercel G and GI guns and sleeve guns (all trademarks noted) in its array construction palette.
- Simple graphical interface to add, edit or delete guns, change the depth of all guns, manipulate sub-arrays, zooming and numerous other shortcuts. Each gun can be individually set in position, gun type, volume and operating pressure allowing complete flexibility.
- Signature characteristics such as peak to peak, primary to bubble and bubble period are produced on demand complete with model error bounds derived from calibration.
- Amplitude spectra and any filtering can be done at the click of a button. The resulting plots are interactive giving an instantaneous check on the signature statistics with just a click of the mouse.
- Sophisticated handling of the surface reflection ghost and optionally the cable ghost using rough sea surface modelling.
- Import and export of signatures in both text and SEGY format.
- Import and export of arrays in text format allowing full arrays with symmetric sub-arrays to be built quickly and easily, (noting that all interactions are always used when actually modelling the array).
- Intranet reporting with comprehensive array report produced in a form suitable for a company Intranet including embedded web graphics for the array geometry, maximum bubble radii, signature and amplitude spectrum and colour contour plots of inline and cross-line directivity and also range/range.
- Sophisticated drop-out analysis using a wide range of industry standard criteria in both the time and frequency domains with automatic identification of illegal drop-out combinations.
- Quick re-modelling of an array signature if a particular dropout occurs. A few clicks to drop-out the relevant guns and Gundalf™ issues a warning of which if any of the specified drop-out criteria have been breached. Since Gundalf™ runs comfortably on a laptop, this means that if a gun goes down during a survey, the effects on the signature can be accurately modelled within a minute - no guesswork and no looking up from tables or databases containing perhaps thousands of combinations. Given that for clustered arrays, the effects of gun drop out are often non-intuitive, this is an invaluable feature.
All the features of Gundalf Designer, plus the following additional functionality:
- The capability of generating sophisticated Intranet reports describing the potential broadband environmental noise impact on marine mammal life. These reports include SPL and SEL plots, swept-depth and particle velocity contours and optionally allow for particular species using NOAA recommendations and include the current best advice available from marine regulatory authorities such as BOEM, EPBC and JNCC. The model output can be adjusted using built-in widely-used bathymetric models to take account of ducting.
- The unique ability to define an inventory of guns and then using sophisticated global optimisation techniques, to design the best array 'ground-up' within the constraints of spectral flatness in a certain region, maximal primary to bubble ratio or a number of other optimisation criteria including specific geophysical objectives such as improving sub-basalt imaging. The resulting arrays are often far superior to those resulting from simple intuition.
- Gundalf™ can be requested to overdraw the inventory (i.e. use more guns of a particular type than are available in the inventory) in which case, it will produce a report at the end of any gun types it felt necessary to overdraw.
- The ability to improve an existing array using the same advanced global optimisation techniques.
- Array signature stability analysis to model the effects of sea-state and optionally pressure variations in the compressor.
The physics behind Gundalf™ is based originally on Laws, Hatton and Haartsen, (1990), "Computer Modelling of Clustered Airguns", First Break, vol. 8, no. 9, (Sept.) which itself builds on earlier published contributions by Anton Ziolkowski, Svein Vaage, Gregg Parkes and Bill Dragoset supported by experimental work done by Tor Haugland, Mike Hall and others. The model solves a complex set of differential equations combining both heat transfer and dynamics.
Over the last 10 years, this has been incrementally refined with modifications to the physics by Les Hatton to handle the 'super-foam' region of colliding bubbles and also to handle innovations such as injector guns and the latest environmentally friendly eSource guns. Periodically over the years, the model has been calibrated against multiple measurements of both non-interacting guns and interacting clusters for all common gun types at a wide range of deployment depths. The model produces signatures within the experimental error of the measurements and accurately models the phase-locking of airgun clusters reported in the above paper.
The model is unconditionally stable for all airgun combinations no matter how close.
See the menu bar for up to date calibration information.
For more details and downloadable papers, see also www.leshatton.org.
Gundalf™ is a leased product, please contact us for a quotation. To purchase a licence, simply email or fax us with a purchase order and we will return instructions for payment and delivery, complete with instructions how to download and install your copy of Gundalf and generate a licence key interactively through our portal.
Thereafter licences may be managed through our online licensing portal 24x7, including the ability to move the licence quickly and simply to another machine if required.
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Gundalf™ is written using an exceptionally portable client-server architecture designed by Oakwood Computing Associates Ltd. The product is available on:-
- Windows 98, 2000, XP (32-bit), Vista, 7, 8, 10 (32/64 bit)
- Linux (glibc 2.x, 32-bit only)
The same source code is used on all these platforms. All calculations are done internally at double precision.