Mid-infrared Reflectance Research Articles

Mid-infrared backscatter characteristics of various benchmark soils

Active mid-infrared laser reflectance characteristics of 18 different benchmark soil samples were measured at different angles of incidence at 9.283, 9.569, 10.247, and 10.633 mu m wavelengths under both copolarized and cross-copolarized conditions. Calibration was performed for each measurement using a Labsphere Infra-fold Diffuse Reflectance Standard of 94% reflectance. One hundred independent samples were averaged for each measurement to yield a mean reflectance value. The soil samples were characterized in terms of the soil taxonomy, mineralogy, geographic location, soil texture, and organic content and represented wide variability in soil properties. The data thus obtained are presented in graphical form, and the effect of soil mineralogy on the spectral features is investigated. A physically based empirical model is also presented to predict the angular dependence of copolarized backscatter. >

Two-Dimensional Vibration Spectroscopy: Correlation of Mid- and Near-Infrared Regions

A novel approach, utilizing a two-dimensional (2D) statistical correlation of mid- and near-infrared spectra, is presented as a means to assist with qualitative spectral interpretation. The method utilizes cross-correlation by least-squares to assess changes in both regions that result from changes in sample composition. The technique has been applied to complex agricultural samples that differ in wax (cuticle), carbohydrate, protein, and lignin content. Dispersive near-infrared (NIR) and interferometric mid-infrared (FT-IR) diffuse reflectance spectra were obtained on each of the samples, and point-for-point 2D cross-correlation was obtained. The technique permits the correlation of the combination and overtone region of the NIR to the fundamental vibrations in the mid-infrared (MIR) region. This allows the determination of the most probable source of NIR signals and verification of the “real” information content of the purely statistically derived signals whose intensities currently are used for quantitative analysis in this spectral region.

Infrared reflectance spectra (4–12 µm) of typical lunar samples

A laboratory study of the mid‐infrared spectral reflectance properties of typical Apollo lunar rock and soil samples was conducted using a modern interferometric spectrometer. The results show that characteristic spectral features exist in the 4–12 micrometer range that are diagnostic of rock composition and mineralogy, especially for the plagioclase‐rich rocks and soils. This is the first phase of a comprehensive infrared reflectance study underway to better understand the use of infrared emission spectroscopy for mapping the surface composition of the Moon and other silicate bodies.

Mapping Surface Albedo in the East Slope of the Colorado Front Range, U.S.A., with Landsat Thematic Mapper

An approach for obtaining surface albedo measurements from Landsat Thematic Mapper (TM) imagery and digital terrain data is presented. Digital terrain data are used for the geometric correction and image registration of satellite imagery, the correction of atmospheric effects, and the computation of solar irradiance. The visible, near-infrared and mid-infrared reflectance derived from Landsat TM spectral bands are combined into a measure of surface albedo by use of a weighted average scheme. The methodology has been applied in order to map the spatial distribution of surface albedo along an altitudinal transect in the east slope of the Colorado Front Range, U.S.A. Estimated values of albedo for selected surfaces compare favorably with published data for comparable surfaces and field measurements in the region. The results presented herein are part of a continuing research project specifically designed to map the spatial patterns of the net radiation load at the surface in high relief environments.

The mid-infrared biconical reflectance of thin films on highly oriented pyrolytic graphite

The biconical reflectance of highly oriented pyrolytic graphite in the MIR spectral region between 4000 and 600 cm −1 has been measured. The use of this material as a substrate for reflection-absorption measurements aiding in scanning tunneling microscopy of protein films is presented.

The effect of metal optical constants on far- and mid-infrared reflection—absorption

Although mid-infrared reflection—absorption spectroscopy is almost routine in some laboratories, the application of this technique to far-infrared spectroscopy is generally acknowledged as a difficult experiment at best. In this report the effect of increasing optical indices with wavelength for metals is demonstrated to be a root cause of this difficulty. When appropriate, iron is a reasonable substrate because of the comparatively small imaginary component of its refractive index in the far-infrared region. In addition, there is only a modest loss in spectral intensity of the spectrum for a film on iron relative to the use of the more noble metals as substrate.

Estimating grassland phytomass production with near-infrared and mid-infrared spectral variables

Near-infrared and mid-infrared spectroradiometric reflectance variables were studied for estimating grass phytomass production within grass plots fertilized with five rates of nitrogen. Nine difference vegetation indices, five single wavelengths, and one waveband were correlated with phytomass. Among the 15 variables studied, TM5 (1550–1750 nm), reflectance at the 1100 nm (R1100), 1650 nm (R1650), and 2200 nm (R2200) wavelengths, and five indices [R1100–R1200, R1100–R1650, (R1100–R1300)-TM5, R1100–R2200, and R1200–R1650] had significant coefficients of determination (r 2) ranging from 0.83 to 0.92. The spectral variables involving the mid-infrared wavelengths generally yielded the highest r 2 coefficients. These results suggest the potential for estimating grass phytomass production over large and inaccesible rangeland areas using Thematic Mapper (TM5 and TM7) satellite data.

The influence of the quasi-two-dimensional character of carriers and corrosion effects on mid-infrared reflectance of YBa 2Cu 3O 7− x

The optical transport properties of the high- T c superconductor YBa 2Cu 3O 7− x are extracted from the infrared spectra at 300 K and 17 K while the absorption feature seen around 3500 cm −1 is attributed to the quasi two-dimensional character of the charge density profile of the carriers. The finer structures seen in the far and mid-infrared regions are related to surface absorption bands characteristic of BaCO 3, CuO and Y 2BaCuO 5 residues accumulating on the surface as a result of corrosion from the atmosphere water and carbon dioxide.

Usefulness of weak bands in midinfrared remote sensing of particulate planetary surfaces

Midinfrared (2.5–25 μm) reflectance spectra of minerals are often used to predict emittance qualitatively. These spectra display weak overtone and combination tone bands, which may be as diagnostic of composition as the strong fundamental molecular vibration bands usually considered for remote sensing applications, but which have been widely ignored. However, unlike the strong bands, the contrast of weak bands relative to the continuum in the midinfrared usually does not decrease with decreasing particle size, but typically increases. To illustrate this behavior, transmittance and reflectance spectra of calcite and quartz are presented for the wavelength range from 4000 to 400 cm−1 (2.5–25 μm). It is the purpose of this paper to point out that these weak bands are potentially useful for compositional remote sensing of particulate planetary surfaces; this will require completion of supporting laboratory studies to document the occurrence of weak bands.

Kramers–Kronig dispersion analysis of LiF reflectance data obtained at ambient and low temperatures*

Room-, liquid-nitrogen-, and liquid-helium-temperature mid-infrared reflectance spectra of lithium fluoride have been measured at near-normal incidence with special emphasis placed on obtaining precise and accurate data in the difficult Rminimum region. The reliability of the measured Rmin curves has been evaluated by a previously suggested mathematical technique. Far-infrared data available from the literature were utilized to construct the low-frequency reflection wings. The newly obtained reflectance data have been processed by an improved Kramers–Kronig dispersion-analysis technique, leading to optical indices significantly more reliable than those reported to date.