Colour Spectrophotometry

Colour Spectrophotometry

Background

Colour is the visually perceived property corresponding in humans to the categories called red, yellow, green, blue and others. Colour derives from the spectrum of light (distribution of light energy versus wavelength) interacting in the eye with the spectral sensitivities of the light receptors. Colour categories and physical specifications of colour are also associated with objects, materials and light sources, based on their physical properties such as light absorption, reflection, or emission spectra. As a result of the factors affecting colour, colour can be very difficult to quantify. Many methods for expressing colour now exist. The most widely known are the RGB, L*a*b*, XYZ, and Munsell colour spaces.

Geoscientists use the Munsell colour system to visually describe the colour of sediments and rocks, comparing the hue, lightness and relative colour purity of earth materials to colour chips. As the demand for a more comprehensive and less subjective colour assessment of sediment and rock is required, Geotek has introduced a state of the art spectrophotometer to mount onto MSCL systems.

CM-700d Spectrophotometer

The CM-700d spectrophotometer is available from Konica Minolta Measuring Instruments (Konica) for integration with a Geotek MSCL system. The vertical alignment of this portable sensor is easily integrated onto the Z-axis sensor arm of each of the Geotek MSCL systems. The small footprint makes this sensor perfect for measuring precisely and repeatedly on curved and flat surfaces.

Operating Principles

The CM-700d spectrophotometer uses a diffused illumination, 8 degree viewing angle with a pulsed xenon lamp providing the illumination. The instrument detector collects light in 10 nm increments between 400 nm and 700 nm wavelength ranges. The spectrophotometric method utilises multiple sensors to measure the spectral reflectance of the object at each wavelength or in each narrow wavelength range. The sensor’s electronics then calculate the tristimulus values from the spectral reflectance data using integration. The measuring aperture is selectable between 8 mm (MAV) and 3 mm (SAV). For each measurement, data for the specular components included (SCI) and excluded (SCE) are recorded simultaneously to analyse the core surface.

Sensor Calibration and Data Processing

The CM-700d spectrophotometer is electronically calibrated to measure a reference piece tested and analysed by Konica. All CM-700d spectrophotometers are supplied with a calibration piece, which can be used to check the long-term consistency of the calibration and repeat the calibration measurement. The calibration is stored internally on the instrument, so if the instrument is switched off, a new calibration will need to be acquired.

The data acquired using the CM-700d spectrophotometer requires very little processing as the calibration is applied to the data during acquisition. The data is displayed visually as spectral values/graphs, colourmetric values and simulated core plots, and the colour spaces are presented as RGB, L*a*b*, XYZ, Munsell colour.

Applications

  • SEDIMENTOLOGICAL LOGGING
    Provides a true colour representation of a unlined whole sediment or rock core, split sediment or slabbed rock surface prior to oxidation
  • PALEOCLIMATE/PALAEOCEANOGRAPHIC RECORDS
    Reflectivity can act as a reliable proxy for carbonate content. Other compositional elements may also be estimated using specific frequencies or colour parameters as proxies.
  • CORE ARCHIVES
    Cross correlation of overlapping core for a continuous downhole colour profile.

Sensor Manufacturer

Konica Minolta.
Website:  http://sensing.konicaminolta.asia/products/cm-700d-spectrophotometer/

For further information on the device see Konica Minolta Spectrophotometer CM-700d or  contact us.