ABI40/OBI40 Image Data Processing
IODP-MSP drilling and logging contractor: ESO
Hole: M0009B
Expedition: 310
Location: Tahiti - Tiarei (central tropical S Pacific)
Latitude: 17° 29.3153' S
Longitude: 149° 24.2044' W
Logging date: October 19, 2005
Sea floor depth (driller's): 114.42 mbrf (100.31 mbsl)
Sea floor depth (logger's): 114.42 mbrf
Total penetration: 26.29 mbsf
Total core recovered: 17.42 m (66.26 % of cored section)
Oldest sediment recovered: Pleistocene sequence
Lithologies: Reef framework, algal crusts, and microbialite matrix
ABI40: 5.78 – 14.74 mbsf
OBI40: 5.18 – 18.82 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.
Optical and acoustic images are generally of high quality in borehole M0009B. Optical images are slightly affected in places by cloudy borehole fluids, although the quality is generally good. A cavity at 13.75 mbsf prevented the acoustic tool from passing above this resulting in a shorter log than the optical log. In general the image logs in borehole M0009B contained such a high level of resolution that identification of changes in the character of the reef framework and separation of the interval over which images were acquired into two main sections.
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.