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At least 487 records · Page 27
All sourcesNASA NTRSDOE OSTI
NASA NTRS2004

Constraints on Early Mars Evolution and Dichotomy Origin from Relaxation Modeling of Dichotomy Boundary in the Ismenius Region

The Martian dichotomy is a global feature separating the northern and southern hemispheres. The 3.5 - 4 Gyr old feature is manifested by a topographic difference of 2-6 km and crustal thickness difference of approx. 15 - 30 km between the two hemispheres. In the Ismenius region, sections of the boundary are characterized by a single scarp with a slope of approx. 20 deg. - 23 deg. and are believed to be among the most well preserved parts of the dichotomy boundary. The origin of the dichotomy is unknown. Endogenic hypotheses do not predict the steep slopes (scarps) of the dichotomy boundary. Exogenic models for forming the northern lowlands by impact cratering, associate the scarps along the dichotomy boundary with craters' rims, but are not globally consistent with the topography and gravity. In order to better understand the origin of the Martian dichotomy, it is necessary to know if the steep scarps along the boundary represent the original shape of the dichotomy. Smrekar et al. presented evidence showing that the boundary scarp in Ismenius is a fault along which the highland crust was down faulted. We test whether the relaxation process could produce faulting along the dichotomy boundary and examine the crustal and mantle conditions that would allow for faulting to occur within 1 Gyr and preserve the long wavelength topography over another 3 Gyr. We approach the problem by a combination of numerical and semi-analytical modeling. We test different viscosity profiles and crustal thicknesses by comparing our modeled magnitude, location and timing of plastic strain and displacements to detailed geologic observations in the Ismenius region.

Guest, A.↗
NASA NTRSDate not supplied

The Origin of Palimpsests

Palimpsests are the most enigmatic impact features observed on icy worlds of the Solar System. Palimpsests are large impact features which are bright, old, mostly flat, and roughly circular. They range from >150 to ~350 km in diameter and sometimes exhibit recognizable associated radial secondary ejecta crater strings beyond their rims. Curiously, among all the Solar System's icy worlds, palimpsests are exclusively seen on the icy Galilean moons. Palimpsests are obviously different than similarly sized impact features seen on other icy satellites. For example, Evander, a 350 km diameter peak-ring impact basin on Saturn’s moon Dione, has a very low depth/diameter ratio of 0.008, indicating significant viscous relaxation. Nevertheless, it still retains short wavelength topography including a prominent central peak, peak ring, and a continuous rim, none of which are seen at palimpsests. Palimpsests display an approximately circular, and dominating, expanse of undulating plains, which is level with surrounding terrain and shows no recognizable rim. At the center of palimpsests are smooth central plains that are enclosed by a low scarp. Central plains material superposes the surrounding undulating plains and is littered with small blocks reminiscent of “small chaos” on Europa. Palimpsests have yet to be explored using modern impact simulation tools. We have begun to investigate two competing hypotheses: (A) Palimpsests form on targets which have a preexisting near-subsurface layer that is liquid or solid but very weak, and is excavated as proximal ejecta; or (B) They form in a solid ice target underlain by a steep thermal gradient that strongly influences the resulting impact feature, including the production of impact-induced melting at depth that is then a major component of proximal ejecta. Our results will have profound implications for the early thermal history of the icy Galilean satellites. We will test our two hypotheses for the formation of palimpsests on Ganymede (where they are both best observed and preserved) by means of 2D iSALE hydrodynamic simulations of impacts into ice targets that will be structured according to the scenarios for each hypothesis, with select runs in 3D. We have already conducted a pilot study using 2D iSALE that has yielded promising results, which we will report out at the meeting.

palimpsests↗
DOE OSTI2020

Brachiopod δ 34 S CAS microanalyses indicate a dynamic, climate-influenced Permo-Carboniferous sulfur cycle

Early isotopic studies of sulfate in carbonate minerals (carbonate associated sulfate; CAS) suggested that carbonates can provide a reliable, well-dated archive of the marine sulfur cycle through time. However, subsequent research has shown that diagenetic alteration can impose highly heterogeneous CAS sulfur isotopic compositions (δ 34 S CAS ) among different carbonate phases within sediments. Such alteration necessitates targeted sampling of well-preserved, primary carbonate phases. Here, we present a new record of Carboniferous and Early Permian brachiopod δ 34 S CAS generated from over 130 measurements of microsampled brachiopod shells. Our record refines existing brachiopod δ 34 S CAS records and confirms a large, ~6.5‰ δ 34 S CAS decrease in the Early Carboniferous. Importantly, the record also features a novel 3–5‰ increase in δ 34 S CAS near the Serpukhovian-Bashkirian boundary (323.4 Ma) that coincides with carbonate δ 13 C and δ 18 O increases. Variability in δ 34 S CAS is minor both within (≤0.3‰) and among (≤2‰) individual co-depositional brachiopod specimens. A taxon-specific δ 34 S CAS offset is present one species (Composita subtilita) that also exhibits a δ 13 C offset, supporting the existence of biological “vital effects” on δ 34 S CAS . Geologic evidence and mathematical modeling of the Permo-Carboniferous carbon and sulfur cycles suggest that changes in the burial ratio of organic carbon to pyrite sulfur (R C:S ) are insufficient to explain the observed mid-Carboniferous δ 34 S CAS record. We find that changes in the 34 S depletion of pyrite relative to seawater sulfate ( 34 ε) or in the δ 34 S of the input to the ocean (δ 34 S in ) are also needed. Large additions of O 2 from organic carbon burial during the Permo-Carboniferous cannot be entirely compensated for with sulfur cycle changes; lower than modern late Visean pO 2 and/or additional O 2 sinks are needed to keep pO 2 at plausible levels. Based on the geologic context surrounding our record's mid-Carboniferous δ 34 S CAS increase, we advocate for simultaneous changes in pyrite burial, 34 ε, and δ 34 S in , driven by sea level or tectonically induced changes in environments of sulfur burial, as a viable mechanism to produce rapid seawater δ 34 S changes.

54 ENVIRONMENTAL SCIENCES↗
NASA NTRS1994

A Study on the Effect of Communication Performance on Message-Passing Parallel Programs: Methodology and Case Studies

From a source-program perspective, the performance achieved on distributed/parallel systems is governed by the underlying message-passing library overhead and the network capabilities of the architecture. Studying the impact of changes in these features on the source-program. can have a significant influence in the development of next-generation system designs. In this paper we introduce a simple and robust tool that can be used for this purpose. This tool is based on event-driven simulation of programs that generates a new set of trace events - that preserves causality and partial order - corresponding to the expected execution of the program in the simulated environment. Trace events can be visualized and source-level profile information can be used to pin-point locations of program which are most significantly affected with changing system parameters in the simulated environment. We present a number of examples from the NAS benchmark suite, executed on the Intel Paragon and iPSC/860 that are used to identify and expose performance bottlenecks with varying system parameters. Specific aspects of the system that significantly effect these benchmarks are presented and discussed,

Sarukkai, Sekhar R.↗
NASA NTRS2004

Teleoperation from Mars Orbit: A proposal for Human Exploration

For a human expedition to Mars, a case can be made that the best strategy for initial exploration is not to actually land the humans on Mars, but to put the humans into Mars orbit and operate on the surface by the technology of teleoperation. This will provide the results of human exploration, but at greatly reduced risk and cost. Teleoperation of Mars surface robots from a Mars-orbital habitat will operation near real time operation with minimum time delay, giving a virtual presence on the surface. By use of teleoperation, it is possible to vastly simplify the surface exploration mission. We now have no need to develop a human-rated Mars Lander and Mars Ascent Vehicle, and we can send geologists & biologists on the mission; not VTOL pilots. It is a cheaper, simpler, and safer way to explore, and hence it will be a faster way to explore. It has the excitement of being there, at a fraction of the price. Tele-exploration from Mars orbit also allows human (virtual) presence at a wide variety of locations. With an orbital base controlling surface telerobotics, human explorers are not stuck with one base location, but can explore all over Mars. They can explore the polar caps and also near-equatorial canyon regions, from the same orbiting base. This frees the mission from landing site constraints. With no need to select a "grab bag" site that contains a large number of geologically diverse features at or near a single location; it is now possible go to all the best sites-- paleolake sites, river beds, volcanic calderas, lava tube sites, layered terrain, canyons, possible shoreline features, the North and South poles. A near-polar inclination 24-hr 39-minute period Mars orbit, for example, will put the orbital station in line-of-sight of a given region for about 8 hours per day-- one teleoperation shift. Since present day life could exist on Mars, planetary protection is also needed to preserve the (possible) fragile Mars biosphere from competition from ferocious Earth life. Isolated biospheres on Earth have been devastated when they have been exposed to alien life forms introduced-accidentally or deliberately-- from another continent. If there is life on Mars, we will wish to protect it from having to compete with introduced Earth biota. Reverse planetary protection-protecting the Earth biosphere from exposure to Mars microorganisms-is also an important consideration. Exploring from orbit will reduce biological risk by keeping humans from exposure to possible Mars microbes. A telerobotic mission will need no quarantine on return to Earth, and avoids the difficult human question of how to isolate Mars mission astronauts infected by Martian microorganisms.

Landis, Geoffrey A.↗
NASA NTRS2012

Examination of Surface Residuals Obtained During Re-Lubrication of the International Space Station (ISS) Solar Alpha Rotary Joint (SARJ)

The starboard SARJ mechanism on the ISS suffered a premature lubrication failure, resulting in widespread loss of the nitride case layer on its 10.3 meter circumference, 15-5PH steel race ring [1, 2]. To restore functionality, vacuum-stable grease was applied on-orbit, first to the port SARJ mechanism to save it from the damage suffered by the starboard mechanism. After 3 years of greased operation, telemetry indicated that the port mechanism required relubrication, so part of that process included sampling each of the three race ring surfaces to evaluate any wear debris recovered and the state of the originally applied grease. Extensive microscopic examination was conducted, which directed subsequent microanalysis of particulate. Since the SARJ mechanism operates in the vacuum of space, a sampling method and tool had to be developed for use by astronauts while working in the extravehicular mobility unit (EMU). The sampling tool developed was a cotton terry-cloth mitt for the EMU glove, with samples taken by swiping each of the three port SARJ race-ring surfaces. The sample mitts for each surface were folded inward after sampling to preserve sample integrity, for return and ground analysis. The sample mitt for what is termed the outer canted surface of the SARJ race-ring is shown in Figure 1. Figure 1 also demonstrates how increasing levels of magnification were used to survey the contamination removed in sampling, specifically looking for signs of wear debris or other features which could be further evaluated using Scanning Electron Microscopy (SEM) methods. The most surprising overall result at this point in the analysis was the relatively small amounts of grease recovered during sampling. It is clear that the mechanism was not operating with surplus lubricant. Obviously, evidence of molybdenum disulfide (MoS2), a major component in the grease applied, was prevalent in the analysis conducted. But a small amount of mechanism wear debris was observed. Figure 2 shows an example of a region of concentrated wear debris. Although some MoS2 is observed, most of the contaminant in this location is nitrided 15-5PH steel, as verified by the associated chemical analysis. High oxygen content was also observed which, when associated with the apparent friable nature of the steel material, suggests that this contaminant could be quite old, perhaps even associated with the mechanism s original manufacture and acceptance testing. Additional microscopic

Martinez, J. E.↗
NASA NTRS1978

Age of graben systems on the moon

The study focuses on the time of formation of the graben. An attempt is made to determine whether the graben are restricted to geologic units of certain ages, and whether and at what time graben formation ceased. It is shown that (1) most preserved graben formed considerably later than the impacts that formed the basins; (2) graben are faults that are reactivated along older basin concentric and radial structures and lunar grid directions; (3) graben formation ceased about 3.6 + or - 0.2 b.y. ago; and (4) graben formation reflects a tensile stress fields that obtained during part of early lunar history. Other features of graben systems on the moon are also identified.

Lucchitta, B. K.↗
NASA NTRS1991

Neuroendocrine abnormalities in patients with traumatic brain injury

This article provides an overview of hypothalamic and pituitary alterations in brain trauma, including the incidence of hypothalamic-pituitary damage, injury mechanisms, features of the hypothalamic-pituitary defects, and major hypothalamic-pituitary disturbances in brain trauma. While hypothalamic-pituitary lesions have been commonly described at postmortem examination, only a limited number of clinical cases of traumatic hypothalamic-pituitary dysfunction have been reported, probably because head injury of sufficient severity to cause hypothalamic and pituitary damage usually leads to early death. With the improvement in rescue measures, an increasing number of severely head-injured patients with hypothalamic-pituitary dysfunction will survive to be seen by clinicians. Patterns of endocrine abnormalities following brain trauma vary depending on whether the injury site is in the hypothalamus, the anterior or posterior pituitary, or the upper or lower portion of the pituitary stalk. Injury predominantly to the hypothalamus can produce dissociated ACTH-cortisol levels with no response to insulin-induced hypoglycemia and a limited or failed metopirone test, hypothyroxinemia with a preserved thyroid-stimulating hormone response to thyrotropin-releasing hormone, low gonadotropin levels with a normal response to gonadotropin-releasing hormone, a variable growth hormone (GH) level with a paradoxical rise in GH after glucose loading, hyperprolactinemia, the syndrome of inappropriate ADH secretion (SIADH), temporary or permanent diabetes insipidus (DI), disturbed glucose metabolism, and loss of body temperature control. Severe damage to the lower pituitary stalk or anterior lobe can cause low basal levels of all anterior pituitary hormones and eliminate responses to their releasing factors. Only a few cases showed typical features of hypothalamic or pituitary dysfunction. Most severe injuries are sufficient to damage both structures and produce a mixed endocrine picture. Increased intracranial pressure, which releases vasopressin by altering normal hypothalamic anatomy, may represent a unique type of stress to neuroendocrine systems and may contribute to adrenal secretion by a mechanism that requires intact brainstem function. Endocrine function should be monitored in brain-injured patients with basilar skull fractures and protracted posttraumatic amnesia, and patients with SIADH or DI should be closely monitored for other endocrine abnormalities.

NASA Program Space Physiology and Countermeasures↗
DOE OSTI2020

Unified Medical Language System resources improve sieve-based generation and Bidirectional Encoder Representations from Transformers (BERT)–based ranking for concept normalization

Concept normalization, the task of linking phrases in text to concepts in an ontology, is useful for many downstream tasks including relation extraction, information retrieval, etc. We present a generate-and-rank concept normalization system based on our participation in the 2019 National NLP Clinical Challenges Shared Task Track 3 Concept Normalization. The shared task provided 13 609 concept mentions drawn from 100 discharge summaries. We first design a sieve-based system that uses Lucene indices over the training data, Unified Medical Language System (UMLS) preferred terms, and UMLS synonyms to generate a list of possible concepts for each mention. We then design a listwise classifier based on the BERT (Bidirectional Encoder Representations from Transformers) neural network to rank the candidate concepts, integrating UMLS semantic types through a regularizer. Our generate-and-rank system was third of 33 in the competition, outperforming the candidate generator alone (81.66% vs 79.44%) and the previous state of the art (76.35%). During postevaluation, the model’s accuracy was increased to 83.56% via improvements to how training data are generated from UMLS and incorporation of our UMLS semantic type regularizer. Analysis of the model shows that prioritizing UMLS preferred terms yields better performance, that the UMLS semantic type regularizer results in qualitatively better concept predictions, and that the model performs well even on concepts not seen during training. Our generate-and-rank framework for UMLS concept normalization integrates key UMLS features like preferred terms and semantic types with a neural network–based ranking model to accurately link phrases in text to UMLS concepts.

96 KNOWLEDGE MANAGEMENT AND PRESERVATION↗
DOE OSTI2021

Human-Constrained Indicators of Gatekeeping Behavior as a Role in Information Suppression: Finding Invisible Information and the Significant Unsaid

To date, disinformation research has focused largely on the production of false information ignoring the suppression of select information. We term this alternative form of disinformation information suppression. Information suppression occurs when facts are withheld with the intent to mislead. In order to detect information suppression, we focus on understanding the actors who withhold information. In this research, we use knowledge of human behavior to find signatures of different gatekeeping behaviors found in text. Specifically, we build a model to classify the different types of edits on Wikipedia using the added text alone and compare a human-informed feature engineering approach to a featureless algorithm. Being able to computationally distinguish gatekeeping behaviors is a first step towards identifying when information suppression is occurring.

96 KNOWLEDGE MANAGEMENT AND PRESERVATION↗
NASA NTRS2008

Geological Mapping of Fortuna Tessera (V-2): Venus and Earth's Archean Process Comparisons

The geological features, structures, thermal conditions, interpreted processes, and outstanding questions related to both the Earth's Archean and Venus share many similarities and we are using a problem-oriented approach to Venus mapping, guided by insight from the Archean record of the Earth, to gain new insight into the evolution of Venus and Earth's Archean. The Earth's preserved and well-documented Archean record provides important insight into high heat-flux tectonic and magmatic environments and structures and the surface of Venus reveals the current configuration and recent geological record of analogous high-temperature environments unmodified by subsequent several billion years of segmentation and overprinting, as on Earth. Elsewhere we have addressed the nature of the Earth's Archean, the similarities to and differences from Venus, and the specific Venus and Earth-Archean problems on which progress might be made through comparison. Here we present the major goals of the Venus-Archean comparison and show how preliminary mapping of the geology of the V-2 Fortuna Tessera quadrangle is providing insight on these problems. We have identified five key themes and questions common to both the Archean and Venus, the assessment of which could provide important new insights into the history and processes of both planets.

Head, James W.↗
DOE OSTI2025

Exotic phases in finite-density ℤ 3 theories

Lattice ℤ 3 theories with complex actions share many key features with finite- density QCD including a sign problem and $\mathcal{CK}$ symmetry. Complex ℤ 3 spin and gauge models exhibit a generalized Kramers-Wannier duality mapping them onto chiral ℤ 3 spin and gauge models, which are simulatable with standard lattice methods in large regions of parameter space. The Migdal-Kadanoff real-space renormalization group (RG) preserves this duality, and we use it to compute the approximate phase diagram of both spin and gauge ℤ 3 models in dimensions one through four. Chiral ℤ 3 spin models are known to exhibit a Devil’s Flower phase structure, with inhomogeneous phases that can be thought of as ℤ 3 analogues of chiral spirals. Out of the large class of models we study, we find that only chiral spin models and their duals have a Devil’s Flower structure with an infinite set of inhomogeneous phases, a result we attribute to Elitzur’s theorem. We also find that different forms of the Migdal-Kadanoff RG produce different numbers of phases, a violation of the expectation for universal behavior from a real-space RG. We discuss extensions of our work to ℤ N models, SU(N) models and nonzero temperature.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2022

Nonlinear quantum behavior of ultrashort-pulse optical parametric oscillators

The quantum features of ultrashort-pulse optical parametric oscillators (OPOs) are investigated theoretically in the nonlinear regime near and above threshold. Viewing the pulsed OPO as a multimode open quantum system, we rigorously derive a general input-output model that features nonlinear coupling among many cavity (i.e., system) signal modes and a broadband single-pass (i.e., reservoir) pump field. Under appropriate assumptions, our model produces a Lindblad master equation with multimode nonlinear Lindblad operators describing two-photon dissipation and a multimode four-wave-mixing Hamiltonian describing a broadband, dispersive optical cascade, which we show is required to preserve causality. To simplify the multimode complexity of the model, we employ a supermode decomposition to perform numerical simulations in the regime where the pulsed supermodes experience strong single-photon nonlinearity. We find that the quantum nonlinear dynamics induces pump depletion as well as corrections to the below-threshold squeezing spectrum predicted by linearized models. We also observe the formation of non-Gaussian states with Wigner-function negativity and show that the multimode interactions with the pump, both dissipative and dispersive, can act as effective decoherence channels. Finally, we briefly discuss some experimental considerations for potentially observing such quantum nonlinear phenomena with ultrashort-pulse OPOs on nonlinear nanophotonic platforms.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2024

Molten flux growth of single crystals of quasi-1D hexagonal chalcogenide BaTiS3

Abstract BaTiS 3 , a quasi-1D complex chalcogenide, has gathered considerable scientific and technological interest due to its giant optical anisotropy and electronic phase transitions. However, the synthesis of high-quality BaTiS 3 crystals, particularly those featuring crystal sizes of millimeters or larger, remains a challenge. Here, we investigate the growth of BaTiS 3 crystals utilizing a molten salt flux of either potassium iodide, or a mixture of barium chloride and barium iodide. The crystals obtained through this method exhibit a substantial increase in volume compared to those synthesized via the chemical vapor transport method, while preserving their intrinsic optical and electronic properties. Our flux growth method provides a promising route toward the production of high-quality, large-scale single crystals of BaTiS 3 , which will greatly facilitate advanced characterizations of BaTiS 3 and its practical applications that require large crystal dimensions. Additionally, our approach offers an alternative synthetic route for other emerging complex chalcogenides. Graphical Abstract

Materials Science↗
DOE OSTI2025

Orientation reversal and the Chern-Simons natural boundary

We show that the fundamental property of preservation of relations, underlying resurgent analysis, provides a new perspective on crossing a natural boundary, an important general problem in theoretical and mathematical physics. This reveals a deeper rigidity aspect of resurgence in a quantum field theory path integral. The physical context here is the non-perturbative completion of complex Chern-Simons theory that associates to a 3-manifold a collection of q-series invariants labeled by Spinc structures, for which crossing the natural boundary corresponds to orientation reversal of the 3-manifold. Our new resurgent perspective leads to a practical numerical algorithm that generates q-series which are dual to unary q-series composed of false theta functions. Until recently, these duals were only known in a limited number of cases, essentially based on Ramanujan’s mock theta functions, and the common belief was that the duals might not even exist in the general case. Resurgence analysis identifies as primary objects Mordell integrals: up to changes of variables, they are Laplace transforms of resurgent functions. Their unique Borel summed transseries decomposition on either side of the Stokes line is simply the unique decomposition into real and imaginary parts. In turn, the latter are combinations of unary q-series in terms of q and its modular counterpart $\overset{\sim }{q}$ , and are resurgent by construction. The Mordell integral is analytic across the natural boundary of the q and $\overset{\sim }{q}$ series, and uniqueness of a similar decomposition which preserves algebraic relations on the other side of the boundary defines the unique boundary crossing of the q series. We demonstrate that this continuation can be efficiently implemented numerically. In the cases where unique mock modular identities are known, they are found by this numerical procedure, but the procedure can go well beyond the known list of identities. A particularly interesting feature of the resurgent approach is that it reveals new aspects, and is very different from other known approaches based on indefinite theta series, Appell-Lerch sums, and representation theory of logarithmic vertex operator algebras.

Chern-Simons theories↗
DOE OSTI2020

$\testit{d}$-wave superconductivity and Bogoliubov-Fermi surfaces in Rarita-Schwinger-Weyl semimetals

In this work, we uncover the properties of complex tensor ($\textit{d}$-wave) superconducting order in three-dimensional Rarita-Schwinger-Weyl semimetals that host pseudospin-$\frac{3}{2}$ fermions at a fourfold linear band-crossing point. Although the general theory of $\textit{d}$-wave order was originally developed for materials displaying quadratic band touching, it directly applies to the case of semimetals with linear dispersion, several candidate compounds of which have been discovered experimentally very recently. The spin-$\frac{3}{2}$ nature of the fermions allows for the formation of spin-2 Cooper pairs which may be described by a complex second-rank tensor order parameter. In the case of linear dispersion, for the chemical potential at the Fermi point and at strong coupling, the energetically preferred superconducting state is the uniaxial nematic state, which preserves time-reversal symmetry and provides a full (anisotropic) gap for quasiparticle excitations. In contrast, at a finite chemical potential, we find that the usual weak-coupling instability is toward the “cyclic state,” well known from the studies of multicomponent Bose-Einstein condensates, which breaks time-reversal symmetry maximally, has vanishing average value of angular momentum, and features 16 small Bogoliubov-Fermi surfaces. The Rarita-Schwinger-Weyl semimetals provide therefore the first example of weakly coupled, three-dimensional, isotropic $\textit{d}$-wave superconductors where the $\textit{d}$-wave superconducting phase is uniquely selected by the quartic expansion of the mean-field free energy, and is not afflicted by the accidental degeneracy first noticed by Mermin over 40 years ago. We discuss the appearance and stability of the Bogoliubov-Fermi surfaces in absence of inversion symmetry in the electronic Hamiltonian, as in the case at hand.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
NASA NTRS1993

Multiscale Morphological Filtering for Analysis of Noisy and Complex Images

Images acquired with passive sensing techniques suffer from illumination variations and poor local contrasts that create major difficulties in interpretation and identification tasks. On the other hand, images acquired with active sensing techniques based on monochromatic illumination are degraded with speckle noise. Mathematical morphology offers elegant techniques to handle a wide range of image degradation problems. Unlike linear filters, morphological filters do not blur the edges and hence maintain higher image resolution. Their rich mathematical framework facilitates the design and analysis of these filters as well as their hardware implementation. Morphological filters are easier to implement and are more cost effective and efficient than several conventional linear filters. Morphological filters to remove speckle noise while maintaining high resolution and preserving thin image regions that are particularly vulnerable to speckle noise were developed and applied to SAR imagery. These filters used combination of linear (one-dimensional) structuring elements in different (typically four) orientations. Although this approach preserves more details than the simple morphological filters using two-dimensional structuring elements, the limited orientations of one-dimensional elements approximate the fine details of the region boundaries. A more robust filter designed recently overcomes the limitation of the fixed orientations. This filter uses a combination of concave and convex structuring elements. Morphological operators are also useful in extracting features from visible and infrared imagery. A multiresolution image pyramid obtained with successive filtering and a subsampling process aids in the removal of the illumination variations and enhances local contrasts. A morphology-based interpolation scheme was also introduced to reduce intensity discontinuities created in any morphological filtering task. The generality of morphological filtering techniques in extracting information from a wide variety of images obtained with active and passive sensing techniques is discussed. Such techniques are particularly useful in obtaining more information from fusion of complex images by different sensors such as SAR, visible, and infrared.

Kher, A.↗