Spectral reflectance was routinely measured for all Leg 178 sites at evenly spaced intervals of 5 cm (2-cm intervals were used for Sites 1098 and 1099) downhole using a Minolta spectrophotometer CM 2002. The basic flow operation in the illuminating/viewing system of the CM 2002 during a measurement is as follows: photon energy from a pulsed xenon arc lamp is thoroughly diffused inside an integrated sphere and provides even illumination over the area of the specimen surface to be measured. The energy reflected from the specimen surface is transmitted by optical fiber cable to spectral sensor 1. At the same time, the energy inside the integrated sphere is transmitted to spectral sensor 2. By using two spectral sensors and measuring both the energy that illuminates the specimen surface and the energy reflected by the specimen surface, the effects of variations in spectral characteristics or intensity of illumination is eliminated. The reflected energy is divided by the wavelength from 4 to 7 µm at a 0.1-µm pitch before striking spectral sensor 1. The sensor converts the received energy distribution pattern into electrical current proportional to the intensity of the energy, then passes the signal to the analog control circuit, where it is subsequently processed in an integrated microcomputer and sent to a storage system via an RS-232C interface. The CM 2002 has an internal software calibration routine and was regularly calibrated against an external light trap and a white (BaSO4 standard) ceramic tile cap.
Measurements were taken as soon as possible after the cores were split to minimize redox-associated color changes that occur when deep-sea sediments are exposed to the atmosphere. The measured diffuse spectral reflectance values (4-7 µm; 0.1-µm pitch) are also used to collect information on sediment color. Therefore, the measured reflectance of a specific spectral energy distribution under standardized conditions is compared with the three basic colors, red, green, and blue. The result of the comparison is expressed as X, Y, and Z, respectively, and called the tristimulus values. The tristimulus values X, Y, and Z are converted to the CIELAB system, which provides values called L*, a*, and b*, where L* is the lightness parameter and a* and b* represent the chromaticity parameters. Additionally, the CIELAB parameters were converted to the Munsell color code. As an aid to defining lithostratigraphic changes during the cruise, the CIELAB system parameters were used to describe changes in the color of cored sediments during Leg 178. Further details are given in the "Explanatory Notes" chapter of the Leg 178 Initial Reports volume (Barker, Camerlenghi, Acton, et al., 1999).
Data sets for each hole consist of sample codes indicating the level at which the measurement was taken, curator depth in meters below seafloor (mbsf), compressed curator depth (mbsf), CIELAB parameter (L*, a*, and b*), Munsell color code, and the values for the spectral distribution (4-7 µm; 0.1-µm pitch).