A New Computerized X-ray Densitometric System for Tree-Ring Analysis

A new facility for X-ray densitometric analysis is in operation at the Laboratory of Tree-Ring Research. Tree-ring specimens are cute to a uniform thickness of 1.0 mm and contact radiographs are produced. The radiographs are scanned by a modified Joyce-Loebl optical microdesitometer interfaced with an Apple II microcomputer. The film optical densities are sampled at 0.02 mm increments and stored on magnetic disks. A battery of computer programs has been developed to edit and process these data, and to transform them into annual time series of various wood density characteristics for each specimen. Several of the programs employ interactive high-resolution graphics to enable the operator to ensure that the resulting series are accurate and complete. Data produced include maximum latewood density, minimum earlywood density, total ring width, average annual density, and integrated annual density. These parameters can be employed as paleoenvironmental indicators.