Strong Atmospheric Absorption Research Articles

Analysis of airborne visible-infrared imaging spectrometer (AVIRIS) data of the Iron Hill, Colorado, carbonatite-alkalic igneous complex

The Iron Hill, Colorado, carbonatite-alkalic igneous rock complex consists mainly of pyroxenite, uncompahgrite, fenite and nepheline syenite, and carbonatite. The study area has been explored intermittently for several decades for thorium, niobium, rare earth elements, titanium, and vermiculite. Airborne visible-infrared imaging spectrometer (AVIRIS) data were acquired for the Iron Hill Complex on August 28, 1992, under clear sky conditions. The data were calibrated using a laboratory reflectance spectrum of a tuff-sagebrush mixture to represent the spectral response of a topographically flat, homogeneous image area within the ash-flow tuff. Analysis of the data was conducted using the spectral angle mapper (SAM) and linear spectral unmixing algorithms in the spectral image processing system (SIPS). Image spectra in the 2.1- to 2.45-mu m wavelength region were used in the SAM method to map dolomite in the Iron Hill carbonatite (rauhaugite) stock and in several smaller bodies, calcite in a small carbonatite (soevite) plug and in travertine spring deposits, illite mainly in sericitized felsite and granite, and kaolinite in hydrothermally altered ash-flow tuff. The general distribution of the main alkalic igneous rocks (pyroxenite, uncompahgrite, and ijolite) was mapped using a full AVIRIS wavelength range (0.40-2.45 mu m) image spectrum of pyroxenite, excluding channels affected by strong atmospheric absorption. However, some areas consisting of felsite and fenite were not spectrally distinguished from the alkalic rocks. Linear spectral unmixing, using full wavelength image spectra, was used to improve the compositional mapping achieved using the SAM algorithm. The fractional abundance images obtained for dolomite and calcite were similar to the SAM results, but the distinction between illite and kaolinite was significantly improved, especially where scattered coniferous trees are present. Hematite and goethite, which showed widely overlapping patterns in the SAM similarity images, were distinguished much better in the fractional abundance images. Biotite was used instead of pyroxenite as a reference end member in the unmixing analysis, and the results were better than those obtained in the SAM analysis...

Observations of Water and Molecular Oxygen in the Interstellar Gas

Water and molecular oxygen are two simple molecules which are not easily observed in the interstellar medium. O2 emissions have yet to be detected from interstellar space, and H2O has been observed only in rather special environments where the interstellar gas has been warmed by embedded infrared sources or by shock waves. This sorry state of affairs does not necessarily reflect a low interstellar abundance for these species, but rather is a consequence of the very high abundance of O2 and H2O within our own atmosphere: strong atmospheric absorption lines make it extremely difficult to carry out observations of water and molecular oxygen emissions using ground-based or even airborne telescopes. Future observations from two orbiting telescopes scheduled for launch in the coming five years - the Infrared Space Observatory (ISO) and the Submillimeter Wave Astronomy Satellite (SWAS) - promise to improve radically the observational data on H2O and O2.

Spectral and Diurnal Variations in Clear Sky Planetary Albedo

Spectral and diurnal variations in the clear sky planetary albedo of the earth are calculated using a radiative transfer model to obtain January and July values for a 5 deg x 5 deg global grid. The model employs observed climatological values of temperatures, humidities, snow and sea-ice cover. The diurnal cycle of clear sky albedo is calculated in the following intervals: 0.2-0.5, 0.5-0.7, and 0.7-4 microns. Observed ozone distribution is specified as a function of latitude and season. The 0.2-0.5 micron spectral albedo is 10-20% higher than the total albedo for all latitudes because of Rayleigh scattering; the 0.5-0.7 micron albedo differs from the total albedo by 1-2% for most latitudes, while the 0.7-4 micron albedo is 5-10% lower than the total because of strong atmospheric absorption. Planetary albedo decreases from morning to local noon, with diurnal variations being particularly strong over water.

Absorption cross-sections of atmospheric gases for use in aeronomy

The current status of absorption cross-section measurements for aeronomic use is reviewed. Recommended values for the gases O2, N2, O, and O3 are given at wavelengths where there is strong atmospheric absorption in the 3500–10 Å region. A table of absorption and ionization cross-sections at important solar emission lines is given. The problem of insufficient resolution at some wavelengths is discussed, and information on photolysis products is given where available.

Mars

THE characteristic appearance of this planetary body, long familiar to astronomers, has of late become generally known. Remarkable neither for situation, magnitude, brilliancy, retinue or complexity of arrangement, inferior in each of these respects to some, and in many of them to several of the members of the solar family, one circumstance alone invests it with a peculiar interest—its resemblance to ourselves. Such a resemblance obviously does not exist in the mightier and more nobly attended external planets: the banded skies of two and the strong atmospheric absorption of the two others revealed by the spectroscope, sufficiently show that they belong to classes mutually indeed dissimilar, but each differing, and perhaps widely, from our own. With the swift and fiery Mercury we can have as little sympathy; and though Venus would offer a more promising analogy, the configuration of her beautiful surface is not well seen or readily interpreted. Mars therefore remains; and while, fortunately for astronomers, he occupies such a position that his features are fairly accessible, they bear an aspect so comparatively intelligible that, whatever may be the case as to our other fellow-subjects in the solar monarchy, we are ready to claim that globe as a close relation of our own, inferior indeed in magnitude and importance, if importance is indicated by an attendant, but arranged in a corresponding manner by the Great Creator as the seat of life and intelligence.