Relative reflectance and complex refractive index in the infrared for saline environmental waters

Abstract

By using distilled water as the standard reflector, relative specular reflectance spectra in the 2-to 20-urn wavelength region of the infrared were measured for surface water samples collected from the San Francisco Bay, the Pacific Ocean, the Atlantic Ocean, the Great Salt Lake (Utah), the Dead Sea (Israel), and an effluent pit of a phosphate mine in central Florida. Phase difference spectra and spectral values of the complex refractive index were computed for each water sample by applying a Kramers-Kronig analysis to the relative reflectance spectra. Spectral values for the complex refractive index suitable for M ie scattering calculations were tabulated for each water sample. The reflectance spectra of the natural saline waters bore great similarity to spectra for individual aqueous solutions containing NaCI, K2SO4, NH4H2POn, NaNO3, and NaHCO3. Chemical analyses of the water samples are also presented in tabular form. INTRODUCTIONThe complex refractive index is denoted by 1½ = n + ik, where the caret denotes a complex number, n is the index of refraction, k is the extinction coefficient, and i represents the square root of minus one. A quantitative knowledge of spectral values of/• for natural waters is presently of considerable interest to many scientists. Such knowledge has application to (1) computer simulations of the transport of electromagnetic radiation through hydrosols, aerosols, and maritime fogs, (2) theoretical investigations of the energy and hydrological balance of the earth's lakes, oceans, and atmosphere, (3) remote sensing of the chemical quality of environmental waters [Querry, 1975], and (4) solar energy development [Chappell and White, 1976]. Querry et al. [1972, 1974, 1976] previously reported measurements of the relative reflectance spectra in the 2-to 20-tzm wavelength region of the infrared for individual aqueous solutions prepared with distilled water in the laboratory. The solutions contained NaC1, H2SO4, K2SO4, NH•H2PO•, NaNOa, or NailCOs. Kramers-Kronig phase shift dispersion analysis of the reflectance spectra for those solutions provided spectral values for N. We observed that mortatomic ions such as Na +, Cl-, and K + perturbed the intramolecular and intermolecular bonds of the liquid water substances so that corresponding wavelength positions of infrared active fundamental vibrational and librational (lattice vibrational) modes were moderately shifted•to shorter and longer wavelengths, respectively. We also explicitly identified 21 infrared active vibrational modes associated with SO• -•, NH4 +, HSO4-, HaO +, HePO4-, NOs-, HCOa-, or H•O. The half width F, central spectral position of each mode X, mode (band) strength So, and maximum value of k were tabulated for each of the 21 modes. These parameters are presented collectively for the first time in Table 1. Band strengths were evaluated by use of Sot =at -• ft, Akt dv (1) where at (in moles per liter) was the molecular density of the ith constituent in the solution, Akt was the part of k due to a Paper number 6C0904. fundamental...

Enhancing mid-infrared surface phonon polariton modes: optimization of structural parameters in Nb-doped SrTiO3 with hole array structures for advanced infrared sensors

“…In the pursuit of a comparative analysis, an examination of five widely recognized optical materials has been conducted. These materials include SiO 2 [27], h-BN [28], SiC [29], GaN [30], and ZnO [31], with the results of this evaluation being presented in figure 2.…”