Near‐infrared (1.3–2.4) μm spectra of alteration minerals—Potential for use in remote sensing

Abstract

Reflection spectra of particulate samples of minerals that commonly occur in hydrothermally altered rocks and soils were recorded to display their features at their natural spectral bandwidths in the near-infrared from 1.3 to 2.4 pm. Atmospheric transmission spectra were recorded over limited wavelength segments in the same region to demonstrate the availability of some of the diagnostic mineral bands that occur close to regions of intense absorption. Changes occur in the appearance of all these spectra caused by instrumental factors such as less than adequate spectral resolution and response time The features in the mineral spectra are sufficiently characteristic to be used for analytical purposes, especially including those near I .4 pm which are unavailable for remote-sensing activities because of atmospheric obscuration. For remote-sensing purposes, the features in the 2.2-km region are emphasized as particularly valuable because they are common to alteration minerals and allow discrimination from nonalteration minerals which provide features-only as-close as?.-Cpm. Detection of unique features near 1.76 pm that occur only in alunite and gypsum is possible through the atmosphere and so provides diagnostic potential. The location and shape of mineral spectral features are retained unaltered in the spectra of rocks, and intensity with which they appear is governed by the accessibility of the particular mineral in the rock to the interacting radiation. For remote-sensing purposes, it appears that at least two 0. I-pm wide filters in the 2.2-pm region would be necessary to unambiguously identify the presence or absence of alteration minerals, and that judicious selection of the exact location of filters could provide finer discrimination.

A standard design for collecting vegetation reference spectra: Implementation and implications for data sharing

“…Numerous references discuss the relationship between physical/biophysical variables and EMR, including: the way in which minerals absorb photons and their associated wavelength dependency (for example, see Hunt and Salisbury, 1970;Hunt et al, 1971a and b;Rowan et al, 1977;Hunt and Ashley, 1979;Hunt, 1977 and1979;Goetz and Rowan, 1981); the spectral reflectance of vegetation (Collins, 1978;Horler et al, 1983;Milton and Mouat, 1989;Boochs et al, 1990;Elvidge, 1990;King et al, 1995;Campbell, 1996;Dawson and Curran, 1998;Datt, 1999 and2000); and, characteristics of soils (Baumgardner et al, 1985;Irons et al, 1989).…”

Spectral properties of weathered and fresh rock surfaces in the Xiemisitai metallogenic belt, NW Xinjiang, China

“…The spectral curve for rhyolite tends to be flat until a broad increase in absorption is visible around 1000 nm (Figure 3a). This absorption is attributed to the effect of ferrous iron and electronic transitions in discrete ions in crystal field absorption (CFA) [37,38]. Weak absorption is visible at 480 nm, 1900 nm, and 2200 nm.…”

“…The weathered surface spectrum is not as strongly affected by ferric iron absorption bands as the fresh spectrum. Relatively, a broad band is centered near 1090 nm, which shows the presence of ferrous rather than ferric iron in the fresh spectrum [37,46].…”

“…A local reflectance peak is present at 2200 nm, followed by a decrease in reflectance with absorption features superimposed at 2250 nm, 2300 nm, 2380 nm, and 2450 nm. Cor- relation of these bands with specific minerals is hampered by the observation that different samples of the same mineral can have absorption bands at different wavelength positions and of different relative strengths [36,37,[49][50][51]. The absorption bands in the sample spectrum appear to be caused by weathering products that consist of both Al-OH and Mg-OH absorption bands.…”

Mapping geological stages of climate-dependent iron and clay weathering alteration on lithologically uniform sedimentary units using Thematic Mapper imagery (Tertiary Duero Basin, Spain)

“…Carbonate registers a moderately wide absorption at 2300 nm, plus several minor minima between 1800 and 2000 nm (Hunt and Salisbury 1971a, Hunt 1979, Lyon and Honey 1979 (figure 2(B)). Such absorptions allow the differentiation between siliceous and carbonated areas.…”