ABI40/OBI40/FAC40 Image Data Processing
IODP-MSP drilling and logging contractor: ESO
Latitude: 17° 46.0445' S
Longitude: 149° 32.8499' W
Logging date: October 28, 2005
Sea floor depth (driller's): 84.76 mbrf (72.15 mbsl)
Sea floor depth (logger's): 84.76 mbrf
Total penetration: 41.08 mbsf
Total core recovered: 29.87 m (72.71 % of cored section)
Oldest sediment recovered: Pleistocene sequence
Lithologies: Reef framework, algal crusts, and microbialite matrix
ABI40/FAC40: 7.05 – 30.31 mbsf
OBI40: 7.01 – 25.95 mbsf
The OBI40 and ABI40 acquired optical and acoustic images respectively at millimetre scale resolution. The optical images provide continuous and color-calibrated images of the borehole wall with a pixel size of less than 1 mm horizontally by 2 mm vertically. The acoustic images show the acoustic hardness of the lithologies within the coral reef sequence with a pixel size of 1.1 mm horizontally by 4 mm vertically.
The images are displayed as an unwrapped borehole cylinder and are provided in .BMP and .PDF format. A dipping plane in the borehole will appear as a sinusoid on the image with the amplitude of this sinusoid proportional to the dip of the plane. The images are oriented with respect to north, hence the strike of dipping features can also be determined. Additional processing on the accelerometer data of the image tools by a double integration of the acceleration allowed, whenever needed, a detailed repositioning of the recorded image data to its correct position with respect to the seafloor.
The ABI40 images of the borehole wall are unaffected by borehole fluid quality. On the other hand, in regions where the borehole fluid was cloudy OBI40 images are of lower quality with a blurred appearance.
Image logs in borehole M00015A were acquired in two stages due to borehole instability. Borehole conditions were hostile, and cavities up to 90 cm are observed below 22.5 mbsf in the image logs. Whilst attempting to obtain a log with the OBI40 it became stuck in a cavity at 27.5 mbsf and tool recovery resulted in cable head damage. In order to continue downhole logging the winch was changed for a backup winch (single conductor cable) and backup single conductor image tools deployed for the remainder of the logging in this borehole. The image quality in the upper optical image is lower, probably due to cloudy borehole fluid. In addition while logging the first few meters of the upper section, the winch sometimes had to pull up to the maximum power. It was thus difficult to remain at a sufficiently low constant logging speed for optimized image quality and the vertical resolution was lowered from 2 mm (as for the lower interval) to 4 mm and logging continued at a higher speed to compensate for these difficulties.
Additional information about the drilling and logging operations can be found in the Operations section of the Site Chapter in IODP Proceedings of Expedition 310. For further questions about the data, please contact:
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