The SharpSeis Adaptive Deghosting module available in RadExPro utilize a stabilized approximate solution for the deghosting operator, applied to a seismic trace in both forward and reversed time. The resulting two traces (primary wavefield without the ghost, and ghost wavefield without the primary) are, then, combined in a non-linear manner in order to maximize the signal and suppress the noise trains, stabilizing the result even further. The optimum ghost delay is estimated adaptively to the data within a sliding window, to ensure the best possible match. This results in sharp crystal-clear seismic images with high signal-to-noise ratio. Some examples are shown below.
Example SharpSeis deghosting on data collected using the P-Cable system and airgun source and deep-towed streamers. The streamers were towed at around 12 m to facilitate deghosting and reduce the noises. Data courtesy of University of Trømso.
In typical marine seismic acquisition, a streamer towed on a given depth records not only an up-going wavefield reflected from the subsurface, but also a down-going field reflected from the sea surface and known as ghost wavefield. Destructive interference of the up-going and the ghost wavefields creates a set of notch frequencies in the recorded spectrum.
The first notch always appears at zero frequency and acts as a high-pass filter suppressing low frequencies, with the slope of the filter dependant on the streamer tow depth. The greater is the tow depth, the more low frequencies are registered in the spectrum.
However, the frequencies of the second and further notches also depend on the streamer tow depth - the greater it is, the lower are the notch frequencies. Since useful bandwidth is commonly limited by the first and the second notch frequencies, towing the streamer deeper, though increases low frequencies, at the same time limits the higher frequencies making the band narrower and compromising the resolution.
synthetic frequency spectrums for data, recorded at different towing depths of the streamer. Blue line represents data spectrum for towing depth of 7.5 meters, green line – 15 meters. The greater streamer depth, the earlier notch frequencies occur, making more low frequencies available, but also limiting high frequencies.
Should the ghost wavefield be removed, this would have both boosted up the low frequencies and cured the notches at high frequencies, thus recovering the full broadband data. However, the problem is that the straightforward analytical deghosting solution is highly unstable and for this reason can hardly be explicitly implemented in any digital processing system.
A number of alternative approaches to acquiring broadband data have been developed instead, involving, along with the data processing, some specific equipment and acquisition techniques, such as dual sensor (combined hydrophone and geophone), over-under (two streamers towed at different depths), variable depth (one streamer is towed in a tilted position). All these approaches, though do produce good data, have one and the same big problem: they make data acquisition complicated and expensive. They also are not applicable to the old data - if one wants it broadband, the only solution is to acquire a new survey.
For further information please contact sales@geomatrix.co.uk.
The new Geomatrix website is here!!
8 January 2016
Over the last few months Geomatrix have been developing a new responsive website. As well as improving the functionality of the website on mobile devices, new tools and additional product information has been added.
New website features include;
Improved product and software relationships.
Recommended product accessories.
Product Search.
Online repair form.
Product shipping weights and dimensions.
A new and improved magnetic Gradient Calculator.
We invite everyone take 5 minutes to browse the new site and ask for feedback or comments to be sent to matt@geomatrix.co.uk.
Ideas for the new Geomatrix website!
26 August 2015
Geomatrix are currently developing a new responsive website and would like to request ideas for supporting content which you would like see included on the product pages. This additional content could take the form of handy documentation, references or videos.
Get 10% discount off the EM34 Conductivity Meter Range
15 December 2014
Geomatrix Earth Science Ltd is pleased to announce that Geonics Ltd is offering a 10% discount off the EM34 conductivity meter range until the 13th of February 2015. The EM34-3 is a fast, simple to operate, cost-effective instrument for the engineering geophysicist, geologist and hydro geologist alike and has been particularly successful for mapping deeper groundwater contaminant plumes and for groundwater exploration.
To receive further information about the product line or/and a quotation contact sales@geomatrix.co.uk
TrackMaker Software Update
2 October 2014
Since Geonics moved to supplying the Archer data logger with its Windows Mobile OS a Key Lock dongle has not been required to run Geomar’s TrackMaker software.
TrackMaker & RTmap software for the EM31MK2, EM38MK2, EM61MK2, G-823 and Grad601-2 is supplied in two parts. Nav31 etc… is the data acquisition package for Windows Mobile. Nav software is activated by a password generated from the data logger serial number.
The newest version of TrackMaker is supplied with a password and are backward compatible with Nav_CX and Nav_DOS data acquisition software. We still supply Key Lock dongle as part of rentals but we will be phasing them out in the near future. The support CD supplied with an EM31MK2, EM38MK2, EM61MK2 and G-823 rental includes the new versions of the software which are located under the ‘Nav-Trackmaker Software’ directory. We will also be uploading the setup files to our ftp site, http://www.geomatrix.co.uk/client-access, so that customers can download the most up-to-date versions. Please contact sales@geomatrix.co.uk to request the Username and Password.
