Spacecraft studies of Phobos and Mars

Utilizing the Termoskan data set of the Phobos '88 mission we have recognized a new feature on Mars: Ejecta blanket Distinct In the THermal infrared (EDITH). Virtually all of the more than one hundred of these features discovered in the Termoskan data are located on the plains near Valles Manneris. EDITH's have a startlingly clear dependence upon terrains of Hesperian age, implying a spatial or temporal dependence on Hesperian terrains. Almost no thermally distinct ejecta blankets are associated with any of the thousands of craters within the data set that occur on the older Noachian units. EDITH's also do not appear on the portions of the younger Tharsis Amazonian units seen in the data. The Hesperian terrain dependence cannot be explained by either atmospheric or impactor variations; Noachian and Hesperian terrains must have experienced identical atmospheric and impactor conditions during Hesperian times. Thermally distinct eject a blankets therefore reflect target material differences and/or secondary modification processes. A further discussion of EIDTH's is presented

Ten Micron Photometry of 25 Stars from B8 To M7

A photometer employing a liquid hydrogen-cooled mercury-doped germanium photoconductor whose spectral response is limited to the 8 - 14 µ region by a low pass interference filter and a BaF_2 window coupled with the cell's threshold wavelength has been placed at the east arm Cassegrain focus of the 200 inch Hale telescope. Twenty-five stars have been measured. The earliest star for which two measurements have been obtained is the B8Ia star β Orionis. The latest star is the M7e star X Cygni. The brightest star, L37 X 10^(-14) watts/cm^2, is α Orionis. The carbon star DS Peg was also measured. In a two-color diagram formed with B and V there is an intrinsic increase in dispersion going to later type stars and a systematic trend away from the blackbody relation. The ratios of the stellar fluxes to those expected from blackbodies at the published stellar effective-temperatures and angular diameters are not far from one. A systematic trend exhibited may not be real because of the assumptions involved in inteferometric diameter determinations. DS Peg does not appear overly peculiar in the two-color plots, but X,Cygni falls on the opposite side of the blackbody curve ("blue excess") compared with most of the late type stars. The fluxes presented here have not been corrected for presently uncertain telescope transmission losses which may be important

Surface Temperature Variations during the Lunar Nighttime

A new photometer incorporating a mercury-doped germanium photoconductor has been used with a 19-inch telescope to measure the 8-14- brightness temperatures of the shaded lunar surface. Right- ascension scans carried into the lunar nighttime from the terminator show a characteristic of cooling inconsistent with the occurrence of a thick homogeneous dust layer. It appears th more highiy conducting material either is exposed commonly on the surface or constitutes a substratum generally covered by no more than a centimeter or so of the strongly insulating dust. No difference in nighttime temperature distribution was observed between maria and uplands. However, local areas of higher-thanaverage brightness temperature were encountered. These indicate extensive exposures of consolidated material. Local temperature anomalies of this type are associated with the bright-rayed craters Tycho and Copernicus, but they are distributed over an area larger than that represented by the respective craters. Two other groups of temperature anomalies were found in otherwise undistinguished mare border areas. These observations and others suggest that surface redistribution processes are operative on the lunar surface over at least a 10-meter range, but are not important over distances much in excess of a kilometer

Merton Davies (1917-2001)

Merton Davies passed away unexpectedly in April at age 83 due to complications from surgery. He will be remembered for establishing the prime meridian for essentially every solid planet in the solar system with the exception of Earth and Pluto. He was an AGU Fellow, and had been a member since 1970 (Planetary Sciences)

Optimal stopping times for estimating Bernoulli parameters with applications to active imaging

We address the problem of estimating the parameter of a Bernoulli process. This arises in many applications, including photon-efficient active imaging where each illumination period is regarded as a single Bernoulli trial. We introduce a framework within which to minimize the mean-squared error (MSE) subject to an upper bound on the mean number of trials. This optimization has several simple and intuitive properties when the Bernoulli parameter has a beta prior. In addition, by exploiting typical spatial correlation using total variation regularization, we extend the developed framework to a rectangular array of Bernoulli processes representing the pixels in a natural scene. In simulations inspired by realistic active imaging scenarios, we demonstrate a 4.26 dB reduction in MSE due to the adaptive acquisition, as an average over many independent experiments and invariant to a factor of 3.4 variation in trial budget.Accepted manuscrip

The Limits of Science

In science, only reproducible, or at least recurrent, observations can be dealt with rigorously. How, then, can scientists attest purported phenomena such as ESP, UFO's, or religious miracles

BIOFUELS, CLIMATE POLICY, AND WATER MANAGEMENT: ASSESSING POLICY-INDUCED SHIFTS ON AGRICULTURE’S EXTENSIVE AND INTENSIVE MARGINS

Biofuel expansion efforts and climate mitigation policy could fundamentally alter land management trends in U.S. agriculture and forestry (AF) by mandating biofuel feedstock production and providing incentives for greenhouse gas (GHG) emissions reduction and carbon sequestration from terrestrial sources. Research has shown that biofuel expansion can alter commodity markets, induce agricultural land expansion, and intensify production. Meanwhile, GHG mitigation efforts could limit agricultural expansion, reduce current cultivation, and lower management intensity by incentivizing GHG emissions reduction and carbon sequestration within AF. To date, little work has attempted to quantify biofuel and climate policy-induced shifts together along the extensive and intensive agricultural production margins within a systems-based framework, though such shifts could have resounding implications on agricultural water consumption and quality. This study uses a comprehensive and detailed economic model of the U.S. AF sectors to simulate land management responses to biofuel expansion and GHG policies. While bioenergy production and altered AF management practices are found to significantly reduce GHG emissions, additional water consumption and nutrient use are possible policy outcomes. Specifically, we find that policies that influence shifts to the extensive margin will increase aggregate water use and nutrient application, but lead to lower intensity per-unit area. Conversely, when combined with biofuel mandates climate mitigation incentives lower agricultural land expansion, but lead to higher levels of management intensity. Somewhat contrary to expectations, GHG mitigation incentives cause water and nutrient use intensity to grow at an increasing rate due to the greater level of land use competition. Additionally, important regional trends emerge, as water use and quality concerns grow with the CO2 price in areas with limited GHG mitigation possibilities. This suggests that “water leakage” is possible whereby emissions reduction activities decrease output in one region and stimulate management intensity elsewhere. The potential indirect consequences of combined biofuel and climate mitigation incentives on water resource systems warrant further attention in policy design and future research.Greenhouse gas mitigation, biofuels, water resource management, Environmental Economics and Policy, Production Economics, Resource /Energy Economics and Policy,

Beyond Binomial and Negative Binomial: Adaptation in Bernoulli Parameter Estimation

Estimating the parameter of a Bernoulli process arises in many applications, including photon-efficient active imaging where each illumination period is regarded as a single Bernoulli trial. Motivated by acquisition efficiency when multiple Bernoulli processes are of interest, we formulate the allocation of trials under a constraint on the mean as an optimal resource allocation problem. An oracle-aided trial allocation demonstrates that there can be a significant advantage from varying the allocation for different processes and inspires a simple trial allocation gain quantity. Motivated by realizing this gain without an oracle, we present a trellis-based framework for representing and optimizing stopping rules. Considering the convenient case of Beta priors, three implementable stopping rules with similar performances are explored, and the simplest of these is shown to asymptotically achieve the oracle-aided trial allocation. These approaches are further extended to estimating functions of a Bernoulli parameter. In simulations inspired by realistic active imaging scenarios, we demonstrate significant mean-squared error improvements: up to 4.36 dB for the estimation of p and up to 1.80 dB for the estimation of log p.Comment: 13 pages, 16 figure

North polar stratigraphy and the paleo-erg of Mars

An accurate self-consistent way of coregistering the imaging and topographic data sets of the Mars Global Surveyor mission was developed and used to begin a stratigraphic analysis of the northern polar region. A distinct change in the layering style exists at a definite stratigraphic horizon near the base of the north polar layered deposits. Occurrences of the contact between two distinct layered units can be mapped hundreds of kilometers apart at nearly the same Mars Orbiter Laser Altimeter (MOLA) elevation. The lower layered unit has a consistent association with sand dunes, leading to the conclusion that it is an eroding sand-rich deposit that predates most of the overlying north polar layered deposits, which exhibits the expected features of a dust-ice mixture. These results suggest that an areally extensive erg was in existence before the present ice cap and that the present circumpolar erg is likely composed of material reworked from this older deposit. The volume of this lower unit is estimated to be on the order of 10^5 km^3. The presence of this deposit implies that there existed a period in Mars' history when there was no icy polar cap. A dramatic climatic change leading to the deposition of the upper layered (icy) unit in the present-day polar layered deposits represents a major event in Mars' history. However, owing to uncertainties in the mechanics of layered deposits formation, such an event cannot be dated at this time