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Hale, A. S.

Publications and source records attributed to Hale, A. S..

18 records
All sourcesNASA NTRSDOE OSTI
NASA NTRS2005

Water Ice Clouds in the Martian Atmosphere: A View from MGS TES

We use the method of Tamppari et al. to map water ice clouds in the Martian atmosphere. This technique was originally developed to analyze the broadband Viking IRTM channels and we have now applied it to the TES data. To do this, the TES spectra are convolved to the IRTM bandshapes and spatial resolutions, enabling use of the same processing techniques as were used in Tamppari et al.. This retrieval technique relies on using the temperature difference recorded in the 20 micron and 11 micron IRTM bands (or IRTM convolved TES bands) to map cold water ice clouds above the warmer Martian surface. Careful removal of surface contributions to the observed radiance is therefore necessary, and we have used both older Viking-derived basemaps of the surface emissivity and albedo, and new MGS derived basemaps in order the explore any possible differences on cloud retrieval due to differences in surface contribution removal. These results will be presented in our poster. Our previous work has concentrated primarily on comparing MGS TES to Viking data; that work saw that large-scale cloud features, such as the aphelion cloud belt, are quite repeatable from year to year, though small scale behavior shows some variation. Comparison of Viking and MGS era cloud maps will be presented in our poster. In the current stage of our study, we have concentrated our efforts on close analysis of water ice cloud behavior in the northern summer of the three MGS mapping years on relatively small spatial scales, and present our results below. Additional information is included in the original extended abstract.

Hale, A. S.↗
NASA NTRS2004

An Investigation of the Correlation of Water-Ice and Dust Retrievals Via the MGS TES Data Set

Water-ice in the Martian atmosphere was first identified in the Mariner 9 Infrared Interferometer Spectrometer (IRIS) spectra. The Viking Imaging Subsystem (VIS) instruments aboard the Viking orbiter also observed water-ice clouds and hazes in the Martian atmosphere. The MGS TES instrument is an infrared inferometer/spectrometer which covers the spectral range 6-50 micron with a selectable sampling resolution of either 5 or 10 per cm. Using the relatively independent and distinct spectral signatures for dust and water-ice, these two retrieved quantities have been retrieved simultaneously. Although the interrelations among the two quantities have been analyzed by Smith et al. and the retrievals are thought to be robust, understanding the impact of each quantity on the other during their retrievals as well as the impact from the surface for retrievals is important for correctly interpreting the science, and therefore requires close examination. An understanding of the correlation or a-correlation between dust and water-ice would aid in understanding the physical processes responsible for the transport of aerosols in the Martian atmosphere. In this presentation, we present an investigation of the correlation between water-ice and dust in the MGS TES data set.

Qu, Z.↗
NASA NTRS2004

Planetary Regolith Microstructure: An Unexpected Opposition Effect Result

The Opposition Effect (OE) is the non-linear increase in the intensity of light scattered from a surface as phase angle approaches 0 deg. It is seen in laboratory experiments and in remote sensing observations of planetary surfaces. Understanding the OE is a requirement to fitting photometric models which will produce meaningful results about regolith texture. Our previous laboratory studies are consistent with the hypothesis that the OE in particulate materials is due to two processes, Shadow Hiding (SHOE) and Coherent Backscattering (CBOE). SHOE arises because, as phase angle approaches zero, shadows cast by regolith grains on other grains become invisible to the observer. CBOE results from constructive interference between rays traveling the same path but in opposite directions. In this study we measured the angular scattering properties of 9 mixtures of Aluminum Oxide and Boron Carbide powders of the same particle diameter (25 microns). The reflectance of the materials ranged from 7% (pure B4C) to 91% (pure Al2O3). Along with the reflectance phase curve we measured the circular polarization ratio (CPR) - the ratio of the intensity of the light returned with the same helicity as the incident light to that with the opposite helicity. An increase in CPR with decreasing phase angle indicates increased multiple scattering and is consistent with CBOE (Hapke, 1993). Popular conceptions of CBOE (Belskaya et al, 2003) hold that materials of higher albedo would exhibit increased multiple scattering and that the contribution of CBOE to the OE would increase as albedo increases. Remarkably, we find the highest albedo samples did not have the strongest CBOE opposition peaks. Instead, the maximum CBOE contribution is observed in samples with reflectance between 15 and 40%.

Nelson, R. M.↗
NASA NTRS2003

Size-dependent Measurements of the Scattering Properties of Planetary Regolith Analogs: A Challenge to Theory

The nature of the scattering of light is thought to be well understood when the medium is made up of independent scatterers that are much larger than the wavelength of that light. This is not the case when the size of the scattering objects is similar to or smaller than the wavelength or the scatterers are not independent. In an attempt to examine the applicability of independent particle scattering models, to planetary regoliths, a dataset of experimental results were compared with theoretical predictions.

Piatek, J. L.↗
NASA NTRS2003

Water Ice Albedo Variations on the Martian Northern Polar Cap

The Viking Orbiters determined that the surface of Mars northern residual cap is water ice. Many researchers have related observed atmospheric water vapor abundances to seasonal exchange between reservoirs such as the polar caps, but the extent to which the exchange between the surface and the atmosphere remains uncertain. Early studies of the ice coverage and albedo of the northern residual Martian polar cap using Mariner 9 and Viking images reported that there were substantial internannual differences in ice deposition on the polar cap, a result which suggested a highly variable Martian climate. However, some of the data used in these studies were obtained at differing values of heliocentric solar longitude (L(sub s)). Reevaluation of this dataset indicated that the residual cap undergoes seasonal brightening throughout the summer, and indicated that this process repeats from year to year. In this study we continue to compare Mariner 9 and Viking Orbiter imaging observations and thermal data of the north residual polar cap to data acquired with Mars Global Surveyor s Mars Orbiter Camera (MOC) instrument. In the current study, our goal is to examine all released data from MGS MOC in the northern summer season, along with applicable TES data in order to better understand the albedo variations in the northern summer and their implications on water transport. To date, work has focused primarily on the MOC dataset. In 1999, data acquisition of the northern polar regions began at L(sub s) = 107, although there was little north polar data acquired from L(sub s)= 107 to L(sub s) = 109. We examined a total of 409 images from L(sub s) = 107 to L(sub s)=148. We have also examined data from 2000 from L(sub s)= 93 to L(sub s)= 110; additional progress is ongoing. Here we present a progress report of our observations, and continue to determine their implications for the Martian water cycle.

Hale, A. S.↗
NASA NTRS2003

Using MGS TES Data to Understand Water Cycling in Mars' North Polar Region

The Martian water cycle is one of the three annual cycles on Mars, dust and CO2 being the other two. Despite the fact that detailed spacecraft data, including global and annual coverage in a variety of wavelengths, have been taken of Mars spanning more than 25 years, there are many outstanding questions regarding the water cycle. There is very little exposed water on Mars today, in either the atmosphere or on the surface although there is geological evidence of catastrophic flooding and continuously running water in past epochs in Mars' history as well as recent (within about 10,000 years ago) evidence for running water in the form of gullies. While there is little water in the atmosphere, water- ice clouds do form and produce seasonal clouds caused by general circulation and by storms. These clouds may in turn be controlling the cycling of the water within the general circulation.

Tamppari, L. K.↗
NASA NTRS2003

A Study of the Opposition Phase Curve in Low Albedo Media

The Opposition Effect, the pronounced non-linear intensity increase in the reflectance phase curve with decreasing phase angle,theta , has long been observed in solar system bodies and in laboratory investigations of the angular scattering properties of particulate media. The size and shape of the phase curve, and the change in linear polarization with theta, have been related to the physical properties of planetary regolith scattering materials. Near zero degrees the increase in reflectance with decreasing phase angle has been attributed to two distinct processes. The first is the elimination of shadows cast between the regolith grains as the phase angle decreases. This is called the shadow hiding opposition effect (SHOE). The second is coherent constructive interference between rays of light traveling along identical but opposite paths in multiply scattering media. This is called the coherent backscattering opposition effect (CBOE).

Nelson, R. M.↗
NASA NTRS2003

Water Ice Clouds in the Martian Atmosphere: A Comparison of Two Methods

To date, the only two data sets offer the potential to examine year-to-year changes in cloud features over an entire Martian year: the Viking Infrared Thermal Mapper (IRTM) data set and the Mars Global Surveyor (MGS) Thermal Emission Spectrometer (TES) data set. We have examined the TES data in the same way in which we examined the Viking IRTM data. This provides water-ice cloud information separated in time by 12 Martian years. Since the data are analyzed with the same method, we obtain a very accurate 'apples to apples' comparison, and can generate a historical record of the subtleties of this annual event. Consequently, it is desirable to compare their results to ours to see what differences exist.

Hale, A. S.↗
NASA NTRS2003

Albedo Variations on the Martian Northern Polar Cap as Seen by MGS

The Viking Orbiters determined that the surface of Mars northern residual cap is water ice. Many researchers have related observed atmospheric water vapor abundances to seasonal exchange between reservoirs such as the polar caps, but the extent to which the exchange between the surface and the atmosphere remains uncertain. Early studies of the ice coverage and albedo of the northern residual Martian polar cap using Mariner 9 and Viking images reported that there were substantial internannual differences in ice deposition on the polar cap, a result that suggested a highly variable Martian climate. However, some of the data used in these studies were obtained at differing values of heliocentric solar longitude (Ls). Reevaluation of this dataset in indicated that the residual cap undergoes seasonal brightening throughout the summer, and indicated that this process repeats from year to year. In this study we continue this work with data acquired with Mars Global Surveyor s Mars Orbiter Camera (MOC) and Thermal Emission Spectrometer (TES) instruments. We use MOC Wide Angel (WA) red filter images

Hale, A. S.↗
NASA NTRS2003

Interannual Comparison of Water Vapor in the North Polar Region of Mars

In order to better understand the current climate of Mars, we seek to understand atmospheric water in the north polar region. Our approach is to examine the water transport and cycling issues within the north polar region and in/out of the region on seasonal and annual timescales. Viking Mars Atmospheric Water Detector (MAWD) data showed that water vapor increased as the northern summer season progressed and temperatures increased, and that vapor appeared to be transported southward . However, there has been uncertainty about the amount of water cycling in and out of the north polar region, as evidenced by residual polar cap visible brightness changes between one Martian year (Mariner 9 data) and a subsequent year (Viking data). These changes were originally thought to be interannual variations in the amount of frost sublimed based on global dust storm activity . However, Viking thermal and imaging data were re-examined and it was found that 14-35 pr m of water -ice appeared to be deposited on the cap later in the summer season, indicating that some water may be retained and redistributed within the polar cap region. This late summer deposition could be due to adsorption directly onto the cap surface or due to snowfall. We seek to understand what happens to the water on seasonal and interannual timescales. We address these issues by examining water vapor in the north polar region of Mars during the north spring and summer period from MGS TES data and by comparing these results to the Viking MAWD results.

Tamppari, L. K.↗
NASA NTRS2002

Scattering Properties of Planetary Regolith Analogs

Samples of well-sorted materials have been studied to determine how their scattering properties change with changing particle size. Additional information is contained in the original extended abstract.

Piatek, J. L.↗
NASA NTRS2002

Thermal Modeling on Planetary Regoliths

The thermal region of the spectrum is one of special interest in planetary science as it is the only region where planetary emission is significant. Studying how planetary surfaces emit in the thermal infrared can tell us about their physical makeup and chemical composition, as well as their temperature profile with depth. This abstract will discuss a model of thermal energy transfer in planetary regoliths on airless bodies which includes both conductive and radiative processes while including the time dependence of the solar input function.

Hale, A. S.↗
NASA NTRS2002

Size-Dependent Scattering Properties of Planetary Regolith Analogs

Particles in a planetary regolith can be treated as independent scatterers when their size is large compared with the wavelength of light. The nature of this scattering, however, is poorly understood as the particle size approaches and becomes smaller than the wavelength. In order to understand this interaction better, the reflectances of well-sorted particulate samples of known composition were measured. This reflectance data was then analyzed to determine how scattering properties change with particle size.

Piatek, J. L.↗
NASA NTRS2001

Scattering Properties of Candidate Planetary Regolith Materials

The laboratory investigation of the scattering properties of candidate planetary regolith materials is an important technique for understanding the physical properties of a planetary regolith. Additional information is contained in the original extended abstract.

Nelson, R. M.↗