Monday, September 25, 2017
Published: Jul 2017
Authors
  • Peter Ramsay
    • Peter Ramsay
    • Company: HYPACK
Categories
  • Data Acquisition Processing

SUB-BOTTOM PROFILING ACQUISITION & PROCESSING IN HYPACK®

The newly launched HYPACK® SUB-BOTTOM is a sub-bottom profiling acquisition and processing software package designed for marine geophysical, engineering & geotechnical site surveys, dredging, mining applications. It’s a simple and easy-to-use solution for most sub-bottom profiling survey requirements. Basic sub-bottom profiling acquisition & processing has been available in HYPACK for the past few years, but during the first quarter of 2017 a considerable amount of effort has been put into improving the stability, memory allocation and features of the program. This article is highlights some of new features and functionality of HYPACK® SUB-BOTTOM.

DATA ACQUSITION

HYPACK SUB-BOTTOM supports data acquisition in most coordinate systems using HYPACK’s comprehensive Geodesy library. The program has drivers to acquire data from any analog sub-bottom profiler (using a National Instruments digital acquisition card) or digital sub-bottom profiling data from the industry’s leading manufacturers. In addition to this, a sophisticated triggering system enables simultaneous acquisition of two different SBP systems with no acoustic interference between the systems (Figure 1).

SUB-BOTTOM DATA PROCESSING

HYPACK SUB-BOTTOM has the ability to load large sub-bottom profiling datasets in SEG-Y or JSF formats. The program stores the project data file lists and user defined processing parameters in XML and Configuration files which makes it easier when re-opening the project again. HYPACK SUB-BOTTOM can read navigation from the SEG-Y (or JSF) file, RAW file or EDT file (Figure 2). In HYPACK MAX (SBMAX) one can edit the navigation in a RAW file for “spikes” and apply the corrected EDT navigation to the sub-bottom profiling data.

Once the data files have been loaded, the sub-bottom profiling data is displayed in the Sub-Bottom Processing window and the navigation data in the View Tracks window; the Settings window is used for the application of data processing parameters (Figure 3). The sub-bottom profiling data can be trimmed to a border file which is very useful if one is only interested in viewing and interpreting a section of the dataset.

The Settings window is used to correct the dynamic range of the data, apply band pass frequency filtering, time varied gain (TVG), bottom tracking, water column blanking (removing water column noise) and swell filtering to the data (Figures 4 & 5). The Dynamic Range tab controls have options to view the data in Bipolar, Rectified or Unipolar modes and apply different color palettes. These controls allow the user to visually enhance various geological surfaces (or strata) without altering the original raw SEG-Y or JSF data. Various exponential TVG curves can be applied to the data as well as user defined TVG curves. These curves can be saved for each line or project and re-imported/applied at any later stage. There is an Auto Range, TVG & Bottom Tracking button under the Display Tab in the Settings menu which can provide initial settings for users not familiar with processing sub-bottom profiling data.

GEOLOGICAL INTERPRETATION

Geological interpretation of sub-bottom profiling data involves reviewing the different reflectors which are evident below the seabed. Individual reflectors represent changes in the reflection amplitude which are generally related to the density of the sub-surface sediments. By digitizing these reflective amplitude anomalies the user can separate the sub-surface geology into units with different sediment/rock characteristics. This thickness of a discrete geological unit, such as an unconsolidated sandy unit, is termed an isopach. HYPACK SUB-BOTTOM supports the digitizing of 20 unique reflectors which can be assigned custom names and colors (Figure 6). Reflector digitizing points (“picks”) can be edited or deleted at any time to modify the interpretation. A handy annotation is also provided which gives the depth and sediment thickness values, at the cursor location point, of each discrete geological unit.

Another useful feature is the ability to be able to color each geological unit as an isopach polygon using a custom color palette and transparency (Figure 7).

The reflector digitizing depths or isopachs (sediment thickness) can be seen plotted on the View Tracks window as digitizing interpretation is progressing (Figure 8). This is a useful quality control tool as the consistency of the interpretation can be gauged by reviewing the interpretation on adjacent or cross-lines.

DATA OUTPUTS & CORRECTIONS

The data interpretations generated from digitizing the various reflective sub-surfaces can be output as ASCII XYZ or HYPACK EDT files. Various corrections can be applied to the data outputs such as:

• Sound velocity correction in the water column (average value or apply a sound velocity profile) and separate velocity corrections for saturated sediment or rock.

• Tide corrections using a HYPACK tide file.

• Layback corrections to the data outputs if these were not specified in HYPACK hardware. If the data were acquired in HYPACK and HARDWARE was correctly figured then the coordinates in the SEG-Y file will be corrected for the sub-bottom profiling sensor position.

• Latency corrections between measurement and transmission to the data acquisition computer.

• Interpretation outputs can be trimmed to a border file.

A separate reference file is generated with each ASCII XYZ file high-lighting the corrections applied to the data.

Screen shots can be captured in various image formats (PNG, JPG or BMP), with or without the superimposed reflector interpretation. A coordinate reference file is produced with each image which allows the image to be used as a vertical seismic curtain in third party software packages.

ADVANCED VISUALIZATION FEATURES

HYPACK SUB-BOTTOM has the ability to produce 3D fence diagrams of the sub-bottom profiling lines with superimposed reflector interpretation and colored isopach polygons (Figures 9 & 10). The fence diagram can be rotated in any direction and the transparency of the data controlled. The fence data can also be trimmed to a border file to highlight a particular area of interest. This is a useful tool for visualizing the data in three dimensions to provide a better understanding of the sub-surface geology.

CONCLUSION

HYPACK SUB-BOTTOM is powerful, simple to use and feature-rich software package designed to meet most sun-bottom profiling requirements. This software is available with the 2017 a release of HYPACK or as a stand-alone package for those uses who only undertake sub-bottom profiling surveys.

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