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Common but unappreciated sources of error in one, two, and multiple-color pyrometry
The most common sources of error in optical pyrometry are examined. They can be classified as either noise and uncertainty errors, stray radiation errors, or speed-of-response errors. Through judicious choice of detectors and optical wavelengths the effect of noise errors can be minimized, but one should strive to determine as many of the system properties as possible. Careful consideration of the optical-collection system can minimize stray radiation errors. Careful consideration must also be given to the slowest elements in a pyrometer when measuring rapid phenomena.
Coloration and darkening of methane clathrate and other ices by charged particle irradiation - Applications to the outer solar system
The results of laboratory experiments simulating the irradiation of hydrocarbon-H2O or hydrocarbon-H2O/NH3 clathrates by charged particles in the outer solar system are reported. Ices produced by condensing and boiling liquid CH4 on an H2O frost surface at 100 K or by cocondensing frosts from gaseous mixtures were exposed to coronal-discharge electron irradiation at 77 K, and the spectral properties of the irradiated surfaces were determined. Significant darkening of the initially white ices was observed at doses of 1 Gerg/sq cm, corresponding to 8-500 yrs of irradiation by Uranian magnetospheric electrons on the surfaces of the principal Uranian satellites, or to total destruction of CH4 in the upper 1 mm of the satellite surfaces after 0.05-3.0 Myr. It is estimated that 10 m or more of icy satellite or comet surfaces would be radiation-hardened to a CH4-free ice-tholin mixture over 4 Gyr.
Exact Rayleigh scattering calculations for use with the Nimbus-7 Coastal Zone Color Scanner
The radiance reflected from a plane-parallel atmosphere and flat sea surface in the absence of aerosols has been determined with an exact multiple scattering code to improve the analysis of Nimbus-7 CZCS imagery. It is shown that the single scattering approximation normally used to compute this radiance can result in errors of up to 5 percent for small and moderate solar zenith angles. A scheme to include the effect of variations in the surface pressure in the exact computation of the Rayleigh radiance is discussed. The results of an application of these computations to CZCS imagery suggest that accurate atmospheric corrections can be obtained for solar zenith angles at least as large as 65 deg.
Time evolution of surface chlorophyll patterns from cross-spectrum analysis of satellite color images
The rate of decorrelation of surface chlorophyll patterns as a function of the time separation between pairs of images was determined from two sequences of CZCS images of the Pacific Ocean area adjacent to Vancouver Island, Canada; cloud-free subareas were selected that were common to several images separated in time by 1-17 days. Image pairs were subjected to two-dimensional autospectrum and cross-spectrum analysis in an array processor, and squared coherence estimates found for several wave bands were plotted against time separation, in analogy with a time-lagged cross correlation function. It was found that, for wavelengths of 50-150 km, significant coherence was lost after 7-10 days, while for wavelengths of 25-50 km, significant coherence was lost after only 5-7 days. In both cases, offshore regions maintained coherence longer than coastal regions.
Coastal Zone Color Scanner atmospheric correction - Influence of El Chichon
The addition of an El Chichon-like aerosol layer in the stratosphere is shown to have very little effect on the basic CZCS atmospheric correction algorithm. The additional stratospheric aerosol is found to increase the total radiance exiting the atmosphere, thereby increasing the probability that the sensor will saturate. It is suggested that in the absence of saturation the correction algorithm should perform as well as in the absence of the stratospheric layer.
A semianalytic radiance model of ocean color
A semianalytical radiance model is developed which predicts the upwelled spectral radiance at the sea surface as a function of the phytoplankton pigment concentration for Morel Case 1 waters. The model is in good agreement with experimental measurements carried out in waters which were not included in the data base used to derive it. It suggests that the observed variability in the radiance is due to variations in the backscattering of plankton and the associated detrital material. The model is extended to include other material in the water, such as dissolved organic material, referred to as yellow substances, and detached coccoliths from coccolithophorids, e.g., Emiliana huxleyi. Potential applications include an improved biooptical algorithm for the retrieval of pigment concentrations from satellite imagery in the presence of interference from detached coccoliths and an improved atmospheric correction for satellite imagery. The model also serves to identify and to interpret deviations from Case 1 waters.
Aerosol analysis with the Coastal Zone Color Scanner - A simple method for including multiple scattering effects
A method for studying aerosols over the ocean using Nimbus-7 CZCS data is proposed which circumvents having to perform radiative transfer computations involving the aerosol properties. The method is applied to the CZCS band 4 at 670 nm, and yields the total radiance (L sub t) backscattered from the top of a stratified atmosphere containing both stratospheric and tropospheric aerosols and the the Rayleigh scattered radiance (L sub r). The radiance which the aerosol would produce in the single scattering approximation is retrieved from (L sub t) - (L sub r) with an error of not greater than 5-7 percent.
Empirical orthogonal function analysis of cloud-containing coastal zone color scanner images of northeastern North American coastal waters
Empirical-orthogonal-function (EOF) analyses were carried out on 36 images of the Mid-Atlantic Bight and the Gulf of Maine, obtained by the CZCS aboard Nimbus 7 for the time period from February 28 through July 9, 1979, with the purpose of determining pigment concentrations in coastal waters. The EOF procedure was modified so as to include images with significant portions of data missing due to cloud obstruction, making it possible to estimate pigment values in areas beneath clouds. The results of image analyses explained observed variances in pigment concentrations and showed a south-to-north pattern corresponding to an April Mid-Atlantic Bight bloom and a June bloom over Nantucket Shoals and Platts Bank.
Color graphics workstations used for simultaneous display of satellite and model data sets
Model-measurement display methods for studying actual or synthetic satellite measurements of cloudiness are developed. Visualization and animation techniques are employed to analyze the data. Two types of animation sequences, one based on Insat IR geosynchronous satellite imagery combined with upper level velocity potentials calculations and isoline depictions of the high amplitude centers of low frequency cloudiness activity, and the other combines a mesoscale cloud model simulation of a severe hail storm and synthetic microwave radiation signatures, are described.
The nature of low-albedo asteroids from 3-micron multi-color photometry
The present broadband and narrowband 1.2-3.5 micron spectrophotometry of 16 low-albedo asteroids encompasses C-, F-, P-, D-, and T-class asteroids, and has been used in an effort to identify low-temperature minerals on their surfaces. Attention has been given to the identification of water of hydration. While G-class asteroids have water-rich surfaces, and I asteroids possess some hydrated silicates, not all class Cs do. Finally, the P-, F-, and T-class asteroids do not seem to possess hydrated-silicate surfaces.
On the effect of X rays on the color of elemental sulfur - Implications for Jupiter's satellite Io
Absorption features arose at 0.42 and 0.52 microns when spectral reflectance measurements were conducted for elemental sulfur allotrope mixtures produced by the exposure of the cyclooctal S(8) allotrope of sulfur to X-rays; while these features due to the presence of short-chain molecules are stable at low temperatures, they fade upon warming of the sample. The hypothesis that X-rays in the Jovian environment would cause other allotropic forms of sulfur to revert to S(8) is contradicted by the fact that these features are not present in S(8) at the same temperature that had not been exposed to X-rays.
Satellite ocean color studies of Antarctic ice edges in summer and autumn
Large areas of elevated phytoplanton pigment concentration were observed using CZCS satellite data in the Weddell Sea marginal ice zone and adjacent regions during the austral summer-autumn transition. Pigment values higher in the south than in the north indicate that, besides the irradiance, there are other factors controlling spatial distributions of the phytoplankton pigment concentrations at this time. Low pigment concentrations (as in observations near the Greenwich meridian) may result from turbulent oceanic and atmospheric forcings during the early stage of sea ice development. The data indicate that the phytoplankton blooms are not only characteristic of the spring/summer period, but also extend into the austral autumn and may contribute significantly to regional productivity.
Global color and albedo variations on Triton
Global multispectral mosaics of Triton have been produced from Voyager approach images; six spectral units are defined and mapped. The margin of the south polar cap (SPC) is scalloped and ranges in latitude from + 10 deg to -30 deg. A bright fringe is closely associated with the cap's margin; form it, diffuse bright rays extend north-northeast for hundreds of kilometers. Thus, the rays may consist of fringe materials that were redistributed by northward-going Coriolis-deflected winds. From 1977 to 1989, Triton's full-disk spectrum changed from markedly red and UV-dark to nearly neutral white and UV-bright. This spectral change can be explained by new deposition of nitrogen frost over both the northern hemisphere and parts of a formerly redder SPC. Frost deposition in the southern hemisphere during southern summer is possible over relatively high albedo areas of the cap (Stansberry et al., 1990), which helps to explain the apparent stability of the unexpectedly large SPC and the presence of the bright fringe.
Simultaneous measurements of ocean surface roughness and atmospheric pressure with a cm resolution two-color laser altimeter
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A color gradient in the soft X-ray diffuse background
It is shown that the deviations of the soft X-ray diffuse background B band to C band intensity ratio from a constant value can be described as a simple dipole-like variation across the sky. In terms of the observed Wisconsin B/C band intensity ratio, the mean value is 0.355, the dipole magnitude is 0.106, and the positive dipole axis points toward l = 168.7 deg, b = 11.2 deg, almost in the galactic anticenter direction. This gradient in the spectral hardness can be due to several causes; the simplest is a temperature gradient in the X-ray emitting plasma of the local cavity from about 10 exp 6.2 K toward the galactic center to about 10 exp 5.9 K in the anticenter direction. While the physical origin of such a temperature gradient is uncertain, the alignment of the dipole with the higher temperature (and absorbed) Loop I region may be significant.
Selection of Landsat TM band and band-ratio combinations to maximize lithologic information in color composite displays
Correlation analyses of Landsat TM data for arid areas and laboratory spectral data for various combinations of minerals indicate that band combination 1-4-7 maximally differentiates lithologic materials in most scenes, but that band combination 1-5-7 is preferable for scenes in which hydroxyl-rich minerals are prominent or of specific interest. Among band ratio combinations, 3/1 - 5/4 - 5/7 ranks high for optimal information display.
A search for spectral units on the Uranian satellites using color ratio images
Twenty multispectral sets of calibrated coregistered Voyager 2 images of the Uranian satellites are analyzed in order to identify spectrally distinct surface units and associate these units with specific endogenic or exogenic surface processes. Several regions on each satellite where significant spectral/compositional diversity could be expected were identified by morphologic unit mapping. All the Uranian satellites were found to exhibit some degree of spectral variability associated with bright impact craters, with the typical trend being that the bright craters and their associated ejecta deposits are less red than the remainder of the satellites by 5 to 30 percent. Oberon shows the greatest variability, followed by Titania and Ariel. Morphologic features on Miranda and Ariel possibly associated with endogenic processes such as tectonism or ice volcanism do not exhibit as high a degree of spectral variability relative to their surroundings as bright impact craters.