Derivation of martian surface slope characteristics from directional thermal infrared radiometry

Directional thermal infrared measurements of the martian surface is one of a variety of methods that may be used to characterize surface roughness and slopes at scales smaller than can be obtained by orbital imagery. Thermal Emission Spectrometer (TES) emission phase function (EPF) observations show distinct apparent temperature variations with azimuth and emission angle that are consistent with the presence of warm, sunlit and cool, shaded slopes at typically ∼0.1 m scales. A surface model of a Gaussian distribution of azimuth independent slopes (described by θ-bar) is combined with a thermal model to predict surface temperature from each viewing angle and azimuth of the TES EPF observation. The models can be used to predict surface slopes using the difference in measured apparent temperature from 2 separate 60-70° emission angle observations taken ∼180° in azimuth relative to each other. Most martian surfaces are consistent with low to moderate slope distributions. The slope distributions display distinct correlations with latitude, longitude, and albedo. Exceptionally smooth surfaces are located at lower latitudes in both the southern highlands as well as in high albedo dusty terrains. High slopes are associated with southern high-latitude patterned ground and north polar sand dunes. There is little apparent correlation between high resolution imagery and the derived θ-bar, with exceptions such as duneforms. This method can be used to characterize potential landing sites by assuming fractal scaling behavior to meter scales. More precisely targeted thermal infrared observations from other spacecraft instruments are capable of significantly reducing uncertainty as well as reducing measurement spot size from 10s of kilometers to sub-kilometer scales.     

The mapping of lunar radar scattering characteristics

This is the first of four articles describing a comprehensive series of radar maps of the entire visible lunar hemisphere carried out at wavelengths of 3.8 and 70 cm and analyzing the echoes in both orthogonal senses of circular polarization. In this paper, the basic techniques of delay-Doppler mapping by radar are developed, and the particular steps employed in mapping the Moon are outlined. Succeeding articles present the results obtained and discuss the way in which these results relate to other, nonradar measurements as well as to the actual lunar surface properties.     

The thermal and radiation exposure history of lunar meteorites

Abstract— We have measured the natural and induced thermoluminescence (TL) of seven lunar meteorites in order to examine their crystallization, irradiation, and recent thermal histories. Lunar meteorites have induced TL properties similar to Apollo samples of the same provenance (highland or mare), indicating similar crystallization and metamorphic histories. MacAlpine Hills 88104/5 has experienced the greatest degree of impact/regolith processing among the highland-dominated meteorites. The basaltic breccia QUE 94281 is dominated by mare component but may also contain a significant highland component. For the mare-dominated meteorites, EET 87521 may have a significant highland impact-melt component, while Asuka 881757 and Y-793169 have been heavily shocked. The thermal history of Y-793169 included slow cooling, either during impact processing or during its initial crystallization. Our natural TL data indicate that most lunar meteorites have apparently been irradiated in space a few thousand years, with most <15,000 a. Elephant Moraine 87521 has the lowest irradiation exposure time, being <1,000 a. Either the natural TL of ALHA81005, Asuka 881757 and Y-82192 was only partially reset by lunar ejection or these meteorites were in small perihelia orbits (≤0.7 AU).     

The galactic infrared/submillimeter dust radiation

Summary The unprecedented quality of the IRAS data prompted a series of papers reinvestigating the origin of the galactic infrared/submillimeter radiation and the nature of the heating sources of the interstellar dust. The scope of this paper is to review the main results of these new studies. Sect. 1 contains a general introduction to the subject and an overview of the earlier work. In Sect. 2 and 3, we summarize our current knowledge on dust properties and on the interstellar radiation field. Then, we present the recent interpretations of the infrared emission of our Galaxy, which are based on the IRAS data: in Sect. 4 we present the results from the galactic disk; Sect. 5 covers the question of the contribution from small dust particles, and in Sect. 6 we describe the infrared radiation from the galactic center. The nature of the heating sources and the origin of the galactic infrared radiation is then discussed in Sect. 7. Finally, Sect. 8 presents a comparison of our Galaxy with external galaxies     

Some orbital characteristics of lunar artificial satellites

In this paper we present an analytical theory with numerical simulations to study the orbital motion of lunar artificial satellites. We consider the problem of an artificial satellite perturbed by the non-uniform distribution of mass of the Moon and by a third-body in elliptical orbit (Earth is considered). Legendre polynomials are expanded in powers of the eccentricity up to the degree four and are used for the disturbing potential due to the third-body. We show a new approximated equation to compute the critical semi-major axis for the orbit of the satellite. Lie-Hori perturbation method up to the second-order is applied to eliminate the terms of short-period of the disturbing potential. Coupling terms are analyzed. Emphasis is given to the case of frozen orbits and critical inclination. Numerical simulations for hypothetical lunar artificial satellites are performed, considering that the perturbations are acting together or one at a time.     

A high speed near infrared photometer for lunar occultation studies

A recently developed near infrared high speed photometer intended for lunar oc-cultation studies is described. The primary scientific objective is to reach milli arc second levels of angular resolution so that circumstellar structure of the occulted sources can be resolved. Near infrared sky brightness close to the lunar limb is also studied. Angular diameter derived from the observed occultation of IRC +20169 is presented and system performance discussed.     

The radiation of microwaves and infrared by slender graphite needles

It has become clear from sources observed by IRAS that there are many examples which attain maximum emission per unit (frequency) bandwidth longward of 100 m. Here, we show that a large emissivity at such long wavelengths can be obtained by needle-shaped particles of free carbon. Indeed for needles with a sufficiently high ratio of length to diameter the large emissivity extends from the infrared through the whole microwave region of the spectrum.     

The lunar atmosphere

In contrast to earth, the atmosphere of the moon is exceedingly tenuous and appears to consist mainly of noble gases. The solar wind impinges on the lunar surface, supplying detectable amounts of helium, neon and ³⁶Ar. Influxes of solar wind protons and carbon and nitrogen ions are significant, but atmospheric gases containing these elements have not been positively identified. Radiogenic ⁴⁰Ar and ²²²Rn produced within the moon have been detected. The present rate of effusion of argon from the moon accounts for about 0.4% of the total production of ⁴⁰Ar due to decay of ⁴⁰K if the average abundance of potassium in the moon is 1000 ppm. Lack of weathering processes in the regolith suggests that most of the atmospheric ⁴⁰Ar originates deep in the lunar interior, perhaps in a partially molten core. If so, other gases may be vented along with the argon.     

Spectral characteristics of lunar impact melts and inferred mineralogy

Abstract– Two suites of lunar impact melt samples have been measured in NASA’s Reflectance Experiment Laboratory (RELAB) at Brown University. Suite 1 comprises seven Apollo 17 crystalline impact melt breccias and seven quenched glass equivalents. Suite 2 is made up of 15 additional impact melt samples (from Apollo 12, 15, 16, and 17) which exhibit a range of textures and compositions related to cooling conditions and glass abundance. A few of these samples have cooled slowly and fully crystallized, and thus have the same spectral properties as igneous rocks of similar texture and composition; they cannot be uniquely distinguished without geologic context. However, most of the impact melts and melt breccias contain either quantities of quenched glass and/or have developed microcrystalline nonequilibrium textures with well‐defined, diagnostic spectral properties. The microcrystalline textures are associated with a distinctive 600 nm absorption feature, apparently due to submicroscopic ilmenite inclusions in a transparent host (typically fine‐grained plagioclase). The reflectance properties of these lunar sample suites contribute to and constrain the identification and characterization of impact melts in remote sensing data.     

A comparison of infrared,radar, and geologic mapping of lunar craters

Between 1000 and 2000 infrared (eclipse) and radar anomalies have been mapped on the nearside hemisphere of the Moon. A study of 52 of these anomalies indicates that most are related to impact craters and that the nature of the infrared and radar responses is compatible with a previously developed geologic model of crater aging processes. The youngest craters are pronounced thermal and radar anomalies; that is, they have enhanced eclipse temperatures and are strong radar scatterers. With increasing crater age, the associated thermal and radar responses become progressively less noticeable until they assume values for the average lunar surface. The last type of anomaly to disappear is radar enhancement at longer wavelengths. A few craters, however, have infrared and radar behaviors not predicted by the aging model. One previously unknown feature - a field strewn with centimeter-sized rock fragments - has been identified by this technique of comparing maps at the infrared, radar, and visual wavelengths.     

The lunar maria

The hypothesis proposed by Gold that the lunar maria are composed of dust is shown to give a detailed explanation of the present appearance of the maria. It is also shown that many bright rays may not have the extent and intensity as they had when they were formed.     

The lunar seismogram

The unexpected and unusual characteristics of the lunar seismogram have given rise to various speculations regarding their origin: secondary ejecta, diffusive wave propagation and wave propagation effects in a self-compacted powder layer with a linearly increasing velocity with depth. Many of the characteristics can be explained, qualitatively, by the simple theory of a self-compacting, dry powder layer for which the velocity varies as the sixth root of the depth. This gives a very low seismic velocity at the lunar surface which, in turn, allows the signal to have a long duration, a lack of correlation between horizontal and vertical displacements, a signal envelope that changes with source to receiver separation and a varying spectrum over the duration of the signal. To explain the long duration of the seismic signal quantitatively, it is necessary to include scattering of the normally incident rays at the surface by shallow surface undulations. The sixth root velocity-depth dependence is consistent with the measured variation, with pressure, of the compressibility and velocity of lunar samples.     

The magnetic characteristics of returned lunar samples and 5heir implications for regolith processes

Magnetic observations yield information about the amount and nature of the magnetic phases present in a sample. They reveal that the predominant magnetic phase in the lunar samples is metallic iron which is sometimes alloyed with nickel and cobalt. In the mare basalts less than 0.1% of metallic iron is present, whereas in the non-mare crystalline rocks several percent of iron has been found in some samples. The soils have approximately 0.5% of iron, which is fine grain, rather pure iron occurring in impact glass. In the recrystallized breccias and the igneous rocks the iron is coarser. Systematic minor variations in metallic iron content in the soils reveal soil maturity trends. Mixing between highland and mare soils can be traced with the Fe²⁺ content. Mare soils differ from highland soils in having a higher value of reduced remanence. The magnetic characteristics of the Apollo 14 breccias are not consistent with the progressive metamorphism of a common starting material. Shock welding in the range of tens of kbs can account for the characteristics of some of the ‘unmetamorphosed’ breccias. Greater shock accompanied by recovery can account for the magnetic characteristics of the ‘recrystallized’ breccias.     

NO infrared radiation in the upper atmosphere

A kinetic model is developed for the prediction of upper atmospheric i.r. radiation from the vibrational bands of NO. The model is appropriate to both the quiescent and aurorally excited nighttime atmosphere and has been exercised to examine the variation in NO radiation levels which can result from both natural atmospheric variability and uncertainties in kinetic parameters. Comparisons between model predictions and i.r. radiance data are presented.     

The sunlit lunar surface

Directional infrared emission from the sunlit lunar surface is determined for the thermal meridian and as a function of observer elevation and azimuth angles at three Sun elevation angles. A study of selected mare sites at full Moon suggests that brightness temperatures are relatively insensitive to changes in certain surface parameters, such as the photometric function, emissivity, and thermophysical properties of the soil. The observed deviations from predictions for an average surface can be accounted for by changes in surface roughness.Deceased 12 January, 1971.     

The lunar disturbance effect

Apollo photographs indicate that the lunar disturbance effect is due to changes in the photometric function of the lunar soil caused by rearrangement of the soil particles, rather than to any physical or chemical differences between the uppermost layer and the underlying materials.Paper presented to the NATO Advanced Study Institute on Lunar Studies, Patras, Greece, September 1971.     

Markaryan galaxies as sources of far infrared radiation

Byurakan Astrophysical Observatory. Translated from Astrofizika, Vol. 30, No. 2, pp. 324–334, March–April, 1989.