opti  |
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optical  |
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| SN | A valid term through 1977. After 1977, use optical spectroscopy, optical spectra, optical properties, optical mineralogy or (as of 1981) optical dispersion or optical extinction as applicable. |
optical methods  |
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| SN | As of 1981, no longer a valid term for GeoRef. See microscope methods. |
optimal filters  |
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| RT | filters | | SN | Added to Thesaurus in 1981. |
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