Visualisation and analysis of marine magnetic data
This webinar describes how global consultants and marine surveyors use Geosoft software to easily work with and manage the rapidly expanding volume of geophysical surveys aimed at detecting unexploded ordnance (UXO), buried utilities, and other seabed contamination. Geosoft's UXO Marine package provides a comprehensive workflow and tools to process, detect, and analyze marine magnetic data for effective site investigation surveys.
Marine surveyors working with individual sensors and multi-sensor magnetometer arrays, as well as horizontal and vertical gradiometers, can use UXO Marine to rapidly and reliably convert high volumes of magnetic data into accurate target detection, mapping, and analysis. This webinar covers:
- The application of Geosoft software for marine geophysics
- Tools for processing and interpreting magnetic data
- Dedicated workflows for detecting buried utilities and UXO with marine magnetic data
- Automated target picking and other specialized capabilities
This webinar will be of interest all who are interested in working with geophysical survey data including: Contractors, Consultants, Geophysicists, Geologists, Program/Project Managers and Data Providers.
Presented by: Sara-Lise Underhay, Geophysical Technical Analyst for Geosoft Europe. Recorded on October 28, 2015.
Audience Questions and Answers
We had so many excellent questions from customers during this webinar that we were unable to answer them all during the session. Here is a list of questions and answers not covered in the video recording. The questions are organized by topic and some similar questions have been edited and combined. Show/Hide All Questions
Q: I've often got a lot of raw data files, do I have to bring them in one at a time or is there a way to import them all at once?
A: You can use scripts (macros) to help import files, however we are working on a new capability to import multiple ASCII files that is expected in the next release, in early 2016.
Q: Is it possible to write a regular expression parser to import arbitrary data?
A: Our existing import tools do not support “regular expressions”. The tools do support numerous common formats and this includes arbitrary formatted ASCII and binary file formats (for a complete list see Supported data files). For several of the import tools you can define templates to automate importing your data files. In addition, you can also use our API – GX Developer and one of the languages that support regular expression parsing (for example C++, C# or Python) to develop an import tool that would accommodate your arbitrary data.
Q: Often in my processing I have to do repetitive tasks. Can I run macros?
A: Yes, you can easily record a macro or script as you run through a processing sequence. Then replay it as is, or make minor modifications depending on the nature of your tasks. It is also possible to create a series of scripts that complete a processing sequence.
Q: Could you talk a little about the influence of line spacing on how you process the data? For example, the difference between typical cable & pipeline survey data (single mag, line spacing's of 100s of m) and UXO-specific data often acquired at a close line spacing?
A: The line spacing should be selected based on the size of the response from the expected targets and the objectives of the survey. However, to answer your question we are assuming for now, that "close" line spacing means that the features can be detected on one or more survey lines, whereas "broad" line spacing refers to surveys where features are detected only on a single survey line. Broadly spaced or independent survey lines should be processed as profiles for filtering, visualization, target picking and analysis. For closely spaced or related survey lines, some processing may be done on the profiles (for example filtering acquisition noise, like heading corrections), but it is better to do much of the processing on grids or raster of the survey data. A good example would be target picking and analysis; if you picked targets from profiles of closely spaced data you likely would pick the same target several times, and it would be difficult to determine the true location of the response from so many picks. In addition, when analysing the target with closely spaced lines we can more reliably model the target by using the response from all the survey lines over the target when calculating the model. UXO Marine has the commonly used tools for processing both broadly spaced (profile or 1D) and closely spaced (grid or 2D) data. We do have other extensions if you need additional tools in either case, such as for filtering, using the Geophysics extension for profile data and MAGMAP for gridded data. A more detailed discussion of the selection of line and sample spacing could be the topic of its own presentation, perhaps something we will consider for next year.
Q: How are you calculating the modified magnetic response when performing the altitude correction?
A: The altitude correction is performed by the continuation of the magnetic data between a series of arbitrary surfaces. The modified magnetic response is calculated by upward or downward continuing all of the data to several discrete altitude levels and then interpolating between them to obtain response at the desired altitude above the sea floor.
Q: Would it be better to perform the (altitude) correction to the sediment floor, rather than an arbitrary survey height above the bottom, to enhance the magnetic response?
A: We do not recommend performing the altitude correction to the sediment or sea floor. Downward continuation of magnetic data amplifies the high frequency content of the data. This high frequency content, can include "noise" and by downward continuing further than is necessarily you can potentially make it difficult to identify targets.
Q: The problem with height or altitude correction is that you if you are upward continuing, you effectively apply a low-pass filter. Is there a way to ensure that no significant information is lost in that step?
A: Yes, you are correct, upward continuing the magnetic data reduces the high frequency content of the data. The only way to ensure that no significant information is lost is to minimize the distance that the data is upward continued. This shouldn't be a significant problem as the data should only be moved up or down by a few meters.
In order to make it easier to reliably identify targets, the purpose of the altitude correction is to help reduce the impact of minor altitude changes of the sensor relative to the sea floor. We do not recommend using it for large scale changes to the data, and suggest you identify or flag areas where the data has been changed significantly and then examine those areas separately or consider resurveying.
Q: To what extent can you downward continue the data? This operation is ill-posed and can damage the data.
A: Yes, this is correct. As discussed above, you should not downward continue the data too great a distance as you will introduce noise. To a large extent, the distance you can correct your data will depend on the quality of the data.
As a general rule, you want to minimize the amount of processing you do to your data, as any processing, if used incorrectly, can damage the data.
Q: Is the altitude correction to the magnetic data performed on a line by line basis?
A: Yes, in UXO Marine the altitude correction is performed line by line, on the selected (or all) lines in the database. Other needs for draping data in various ways can be found in the Compudrape extensions for Oasis montaj, if needed.
Q: Is the analytic signal computed for each line separately? Even for single mag?
A: This depends on your data, as we include several tools that can be used to calculate the analytical signal. If you have a sensor array that has measured either all three gradients, or at least the horizontal gradient, the (3D) analytical signal can be calculated line by line. For the case of the only a measured horizontal gradient, the vertical gradient is first determined using a Fast Fourier Transform (FFT) prior to calculating the analytical signal; whereas if all three gradients are measured, the analytical signal can be directly calculated.
For a single magnetic sensor, currently the data coverage must be dense enough to be able to grid the data. The resulting 2D grid along with FFT calculations are used to calculate the analytical signal. In the next release of UXO Marine you will also be able to calculate the (2D) analytical signal, using FFT's from a single sensor for each line separately.
Q: Can analytical signal be applied to gradient data as grid (2D)?
A: An analytical grid can be calculated from a grid of vertical gradient data; this feature currently exists in the UXO Land toolset (UX-Detect + UX-Process) and will be available in the next release of UXO Marine. In addition, the MAGMAP extension has the ability to do this type of data processing and other grid filtering.
Q: How much is the analytic signal peak shifted toward the true XY target location?
A: The peak of the analytic signal anomaly is centered over the magnetic source body.
Q: Should I use RTP (Reduction To the Pole) filter before calculating the Analytic Signal?
A: No - there is no need to calculate RTP prior to calculating the analytical signal. The analytic signal (also sometimes referred to as total gradient), is a common alternative processing method to RTP. Analytic Signal has been found to be more reliable for calculating source locations, as it does not depend on knowing the regional magnetic field, the effects of magnetic remanence or distortion of the data at low magnetic latitudes.
Q: Clients often want peak to peak anomaly size and peak magnetic values in nT. How does UXO Marine provide these parameters?
A: At this time UXO Marine does not provide a peak-to-peak or dipole size. However, currently in the UXO Land toolset (UX-Detect + UX-Process) this is possible from gridded data using the Find Magnetic Dipoles tool. The tool will find the location and magnitude of the positive and negative peaks along with the location of the inflection point. We are reviewing whether this functionality should be included in UXO Marine, and appreciate your feedback.
Q: How is the horizontal gradient taken into account in the analysis, when using horizontal gradient systems?
A: When using horizontal gradient systems, we can use the measured gradient as opposed to a mathematically calculated gradient in calculating analytic signal for profile or line data. Measured gradients tend to produce a cleaner (less noisy) result when calculating the analytical signal. For surveys with line separations suitable for gridding, the additional data will provide better gridding results, also you can also consider using the gradient option in Bi-Directional Line gridding. The additional sensors of the gradient systems also improve modeling results substantially.
Q: Can you calculate "apparent weight" or "magnetic mass" in UXO Marine?
A: Yes, you can calculate the apparent weight, also referred to the as the magnetic mass. The apparent mass is determined from the magnetic data by using a look-up table or nomogram. Theoretical and empirical studies have shown that using the analytical signal (which is directly related to the magnetic moment) and depth of a magnetic source, the apparent mass can be determined. Also see Information relating to target weight.
Q: Rather than apparent weights, estimated magnetic moments would be a more useful parameter. Are there any plans to integrate this in UXO Marine or the other tools?
A: The existing Batch modelling tool will return a magnetic moment. We are currently working to improving the batch modelling routine to make it more robust. We are also investigating if there are other methods that can be reliably used to calculate a magnetic moment.
Q: Can you model data which are not altitude corrected?
A: Yes – you can model your data without correcting for altitude. If the altitude is reasonably consistent or you are modelling using the profile data, you do not need to perform an altitude correction. We recommended the altitude correction in situations where you are combining the data together from several adjacent survey lines (for example when gridding the data), as often the sensor’s altitude will change from line to line.
Q: Can you model data with the background not removed?
A: Yes – you can model your magnetic data without removing the background. However, when processing data used in the detection of UXO we recommend processing the data to remove the background (for example IGRF, diurnal, or geology) as it makes it easier to identify anomalous features caused by UXO. If the objective of your survey isn’t UXO we have several other modelling tools that may be better suited for your survey. To learn more about these contact the Geosoft account executive for your region or send an email to firstname.lastname@example.org for somebody to contact you.
Q: Can I integrate with other types of data like sonar and multi-beam data?
A: Yes – you can bring in and display results from sonar data, along with your magnetic and any other spatial data and images. Typically sonar data are brought in as gridded spatial datasets or images such as GeoTIFF. These images can be dynamically linked in maps to compare different target locations. We do not provide specialized processing specific to sonar data.
Q: It would be very helpful to view ENCs (Electronic Nautical Charts) in Oasis montaj during the interpretation / visualisation of survey data. Can this format be imported into Oasis montaj?
A: We currently cannot import ENC into Oasis montaj. We are reviewing whether this functionality should be included in UXO Marine, and appreciate your feedback.
Q: Can you export to GIS?
A: Yes – we support a wide variety of GIS data formats, such as Shape (SHP) and Layer (LYR) files. For a complete list see Geosoft Data Support. We also provide free plug-ins for ArcGIS, MapInfo and ER Viewer (see Software Downloads) to directly read the Geosoft file formats.
Q: Do you have any tools for Marine EM (electromagnetic) surveying?
A: Yes, we have an extensive suite of tools for working with electromagnetic data in our UXO Land toolset (UX-Detect + UX-Process). These tools are designed for land surveys but are generally applicable to any EM dataset. You can import your EM data, visualize your data in grids (raster) and pick targets etc. To handle the specific EM data corrections etc., you would currently need the UXO Land toolset (a relatively inexpensive upgrade to UXO Marine, or vice versa). The EM workflow is not yet configured specifically for marine surveys as the magnetic workflow has been. We expect to add these specific capabilities as the demand for marine EM survey work increases.
Q: Are there any other filters that I can apply?
A: Yes, there are many filtering options and filtering extensions available in Oasis montaj, which are useful for many different types of surveys and data. In addition to the database and other filters provided in UXO Marine, there are also other 1D and 2D FFT filters in the Geophysics and MAGMAP extensions.
Q: Is the UXO Marine tool recently developed by Geosoft?
A: Yes - the new workflow and tools in UXO Marine were originally developed by Geosoft in 2013, based on our large set of UXO tools for land surveys. We are continually working to update and improve the marine workflow and tools. To address a number of customer feedback comments, we expect to release our next update in early 2016.
Q: How much does the UXO Marine module cost?
A: Please speak to the Geosoft account executive for your region or send an email to email@example.com for somebody to contact you. If you already have Oasis montaj and UX-Detect it is very affordable to add UXO Marine as an upgrade. There are many options including perpetual licenses and subscriptions of varying lengths to suit your project needs. There is also an online self-service capability now available for established customers wishing to subscribe to the software at any time of the day or night. We can also work with larger customers to meet their specific needs.
Q: I've been using UX-Detect for the last 4 years, what are the benefits to switching to UXO Marine?
A: We would recommend upgrading to UXO Marine if you are doing marine magnetic surveys. There is significant overlap between the systems and therefore the upgrade cost is low. Both have data corrections, target picking tools, modeling, mapping and other capabilities. But the UXO Marine workflow is better suited to the marine geophysics task, and there are added features for this purpose, including:
- Data correction tools for navigation, altitude, and background removal
- Efficient handling of gradient data and arrays
- PotentQ (Inversion based parametric style modelling), that can also be used for forward modelling.
You can see a comparison of the main differences between UX-Detect and UXO Marine in the UXO Product Comparison Chart.
Q: Would my client or my boss need to have the software to look at maps and data that I produce?
A: No - there are many options available for this purpose, at no cost. They could download the free Oasis montaj viewer to look at any of the maps or data that you produce. They will be able to open projects to view and move around in databases and maps, just as you can. They cannot create or process data in the Viewer, but they do have the ability to export files to other formats. We support exporting data, maps, and 3D views to interactive PDFs, GIS formats, standard images and many other file formats.
Q: Why should I pay for this software from Geosoft when many of these capabilities can be done with open-source tools?
A: There are many reasons why customers are happy to work with our software. It takes a huge investment of expertise, time, and resources to investigate and work with open source or other less sophisticated toolsets. Our customers get many benefits from working with Geosoft, including:
- Worldwide, responsive technical support 20 hours/day
- An integrated and robust system that provides a depth of capabilities in one package so that people do not need to move around between packages or change data formats
- A logical workflow to help non-geophysicists understand the necessary steps in processing
- Ability of users to script the processes and thus build customized workflows and routines (saving thousands of dollars in personnel time and internal training)
- Ability to handle very large datasets
- Integration with all other types of geospatial data
- Complete mapping and visualization tools, with cursor linking between data/profiles/grids and 3D views
- A reliable, sustainable supplier who will still be here in 10 years and beyond
- Ongoing updates and enhancements based on customer feedback
- Ongoing support of all new operating systems and related technologies (64-bit support is a good current example)
- Rigorous, state of the art testing procedures for the integrated system, for every release
- Ability to have your developers build your own menus or functions (or have geosoft provide custom development services)
- A host of additional optional software extensions, all integrated for related geophysical applications
- Online e-learning tools
- Available training in all regions around the world
- Many other advantages.
Q: Is PotentQ an add-on module?
A: PotentQ is the interactive modeling tool that was shown briefly in the webinar. It is included as part of the UXO Marine package. It is also available on its own as a separate add-on extension within Oasis montaj. Oasis montaj is the core software platform for all extensions including UXO Marine, PotentQ and many other geophysical specialty tools.
Q: How do I get started / how do I learn how to use the tools?
A: There are many online e-learning tools available at My Geosoft such as Learning Paths that guide you through the steps in the process and to learn the tools as well as a knowledge base of frequently asked questions. You can also arrange personal training and technical time with our technical experts like Sara Lise - actually this is their main job. Our customers derive huge benefit from working through their own datasets and addressing all their workflow needs with our Technical Analysts, in this way.