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AssigneeCalifornia Institute of Technology
InventorsAlexander F. H. Goetz, Richard A. Machida
Estimating the term…
A hand-held instrument is provided to compare information from selected infrared and visible bands in the 0.4 to 2.5 micrometer range, to perform ratioing via a dividing circuit (17) and to directly read out, via a display system (18), ratio values in a continuous digital display. The dual-beam, ratioing radiometer contains two optical trains (10, 12), each having two repeater lenses (L1a, L1b and L2a, L2b) and a cooled lead sulfide detector (D1, D2). One of the trains (10) is pivotal to facilitate measurements at distances ranging from about 1 meter to infinity. The optical trains are intersected by a set of two coaxially-mounted filter wheels (F1, F2), each containing up to five interference filters and slits to pass radiation filtered by the other. Filters with band passes as narrow as 0.01 micrometer are used in the region 0.4 to 2.5 micrometers. The total time for a calibration and measurement is only a few seconds. It is known from previous field studies using prior art devices, that materials, e.g., clay minerals, and carbonate minerals such as limestone, have unique spectral properties in the 2.0 to 2.5 micrometer region. Using properly chosen spectral filters, and ratioing the signals to remove the effect of topography on the brightness measured, the instrument can be used for real-time analysis of reflecting materials in the field. Other materials in the broader range of 0.4 to 2.5 micrometers (and even beyond) could be similarly identified once the reflectance spectrum of the material is established by any means.
A method for providing instantaneous identification of particular reflecting materials by ratioing reflectance measurements at selected pairs of wavelength bands, each band of a pair being chosen for a particular spectral characteristic of a material of interest selected from a group consisting of spectral peaks and band wings on either side of spectral peaks for each band reflected from a particular material, comprising the steps of selecting a plurality of different paired bands, one pair at a time, for instantaneous band ratioing, simultaneously detecting the intensity of radiation reflected by materials under investigation into said plurality of predetermined bands centered on spectral characteristics of the different materials, determining the ratio of radiation intensity in at least one band to the radiation intensity in other bands, and displaying the band ratio thus determined to provide a ratio display indicative of the particular material, whereby a reflecting body can be checked for the presence of a plurality of different materials identified by at least one particular band ratio value for each material.
Apparatus for identifying an unknown material in a target area that reflects radiation within predetermined selected bands comprising
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