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NASA NTRS1981

Multilevel measurements of surface temperature over undulating terrain planted to barley

A ground and aircraft program was conducted to extend ground based methods for measuring soil moisture and crop water stress to aircraft and satellite altitudes. A 260ha agricultural field in California was used over the 1977-78 growing season. For cloud free days ground based temperature measurements over bare soil were related to soil moisture content. Water stress resulted from too much water, not from lack of it, as was expected. A theoretical examination of the canopy air temperature difference as affected by vapor pressure deficit and net radiation was developed. This analysis shows why surface temperatures delineate crop water stress under conditions of low humidity, but not under high humidity conditions. Multilevel temperatures acquired from the ground, low and high altitude aircraft, and the Heat Capacity Mapping Mission (HCMM) spacecraft were compared for two day and one night overpasses. The U-2 and low altitude temperatures were within 0.5 C. The HCMM data were analyzed using both the pre- and post-launch calibrations, with the former being considerably closer in agreement with the aircraft data than the latter.

Reginato, R. J.↗

NASA NTRS1984

A comparison of satellite Doppler and gravimetric geoid undulations considering terrain-corrected gravity data

Geoid undulations derived from Doppler satellite positioning are compared with corresponding values derived from terrestrial and satellite information using three different procedures. Doppler undulations are compared with uncorrected gravimetric undulations, and systematic differences of 1.6 m and 0.4 m are found for western and eastern U.S. stations, respectively. The systematic difference of 1.6 m was reduced to 0.1 m when terrain-related corrections were applied. Undulations computed from a spherical harmonic expansion to degree 180 yielded standard deviations only slightly poorer than the combined data. A more systematic difference in the western than in the eastern stations remained.

Rapp, R. H.↗

NASA NTRS2013

Mechanism for Deploying a Long, Thin-Film Antenna from a Rover

Observations with radio telescopes address key problems in cosmology, astrobiology, heliophysics, and planetary science including the first light in the Universe (Cosmic Dawn), magnetic fields of extrasolar planets, particle acceleration mechanisms, and the lunar ionosphere. The Moon is a unique science platform because it allows access to radio frequencies that do not penetrate the Earth's ionosphere and because its far side is shielded from intense terrestrial emissions. A radio antenna can be realized by using polyimide film as a substrate, with a conducting substance deposited on it. Such an antenna can be rolled into a small volume for transport, then deployed by unrolling, and a robotic rover offers a natural means of unrolling a polyimide film-based antenna. An antenna deployment mechanism was developed that allows a thin film to be deposited onto a ground surface, in a controlled manner, using a minimally actuated rover. The deployment mechanism consists of two rollers, one driven and one passive. The antenna film is wrapped around the driven roller. The passive roller is mounted on linear bearings that allow it to move radially with respect to the driven roller. Springs preload the passive roller against the driven roller, and prevent the tightly wrapped film from unspooling or "bird's nesting" on the driven spool. The antenna deployment mechanism is integrated on the minimally-actuated Axel rover. Axel is a two-wheeled rover platform with a trailing boom that is capable of traversing undulated terrain and overcoming obstacles of a wheel radius in height. It is operated by four motors: one that drives each wheel; a third that controls the rotation of the boom, which orients the body mounted sensors; and a fourth that controls the rover's spool to drive the antenna roller. This low-mass axle-like rover houses its control and communication avionics inside its cylindrical body. The Axel rover teleoperation software has an auto-spooling mode that allows a user to automatically deploy the thin-film antenna at a rate proportional to the wheel speed as it drives the rover along its trajectory. The software allows Axel to deposit the film onto the ground to prevent or minimize relative motion between the film and the terrain to avoid the risk of scraping and antenna with the terrain.

Lazio, Joseph↗

NASA NTRS2024

Computing Proximity to Threat Along Uncertain Trajectory to Support Urban Air Mobility

Many airspace threats affect the selection of a flight route, such as terrain, physical obstacles, adverse weather, and special-use airspace, among others. Threat avoidance during Urban Air Mobility (UAM) and Low Altitude Mobility (LAM) flights is especially challenging due to their lower cruising altitudes. These operations may be exposed to buildings, towers, trees, terrain undulations, etc., along much of their flight route. Moreover, these low-altitude flights in urban environments are expected to encounter very busy airspace, increasing the workload associated with threat avoidance. The Proximity to Threat (PtT) function aims to support onboard or remote pilots by computing the risk from geospatial threats in the airspace along an aircraft’s flight path. The threats are both static entities and dynamic airspace restrictions that have been modeled and stored in geo-referenced mapping databases. The flight path may be specified by waypoints, airways, or similar discrete route elements or by a time series of closely spaced position and altitude points. Flight path uncertainty can also be taken into account by assuming both the position and altitude to be sampled from two normal distributions, each being specified by a mean and variance. PtT uses this additional information to verify that the flight path remains clear of threats along a wider path or if a position is reached earlier or later than anticipated, assuring the pilot or operator that there will be an available safety margin even if the aircraft deviates due to one or more occurrences of unexpected wind gusts, mechanical failures, airspeed changes, collision avoidance maneuvers, etc. The client can specify an uncertainty confidence level to bound the set of trajectories evaluated for threats so that the confidence level corresponds to the client’s risk tolerance under the expected conditions. PtT can be used as a pre-flight planning tool to determine a safe route through known threats and in-flight to avoid emerging or changing threats. In this report, we present the PtT function, discuss how the trajectory uncertainty is incorporated into the PtT function, and describe the use of this PtT function in a representative scenario.

urban air mobility↗

NASA NTRS1979

Evolution of Martian polar landscapes - Interplay of long-term variations in perennial ice cover and dust storm intensity

The discovery of a new type of Martian polar terrain, called undulating plain, is reported and the evolution of the plains and other areas of the Martian polar region is discussed in terms of the trapping of dust by the perennial ice cover. High-resolution Viking Orbiter 2 observations of the north polar terrain reveal perennially ice-covered surfaces with low relief, wavelike, regularly spaced, parallel ridges and troughs (undulating plains) occupying areas of the polar terrain previously thought to be flat, and associated with troughs of considerable local relief which exhibit at least partial annual melting. It is proposed that the wavelike topography of the undulating plains originates from long-term periodic variations in cyclical dust precipitation at the margin of a growing or receding perennial polar cap in response to changes in insolation. The troughs are proposed to originate from areas of steep slope in the undulating terrain which have lost their perennial ice cover and have become incapable of trapping dust. The polar landscape thus appears to record the migrations, expansions and contractions of the Martian polar cap.

Cutts, J. A.↗

DOE OSTI2026

A Linear Programming Approach to Backtracking for Single-Axis Trackers on Rolling Terrain

In this article, we present a computationally efficient method for determining optimal backtracking rotations for single-axis solar trackers on nonuniform terrain. The method allows for ganged tracking, mechanical rotation constraints, uneven row spacing, and arbitrary maximum allowable shaded fractions (to enable “fractional backtracking”). As with previous 2-D approaches, the method is suitable for terrain that varies in the transverse direction with respect to the rotation axis of the trackers. The novelty of the method lies in formulating the problem of shade avoidance as a linear problem, which is achieved by using the row interception width as the optimization variable instead of rotation angles. Formulating backtracking as a linear problem enables the use of extremely efficient linear programming algorithms, making the method highly scalable, requiring less than 1 min to compute optimal rotation schedules for hundreds of trackers. It also produces more effective backtracking rotations, reducing the frequency of shading by 4× and improving system energy output by 1%–2%.

Optimization↗

NASA NTRS1977

The geology of the Viking Lander 1 site

Stereo pictures show that Viking Lander 1 landed on volcanic terrain of undulating topography in the plains of Chryse. The bedrock is exposed along several ridge crests, and blocks are more numerous than can be attributed to impact ejecta. The presence of a variety of rock types suggests in situ weathering of extrusive and near-surface basaltic igneous rocks along a linear volcanic vent. Fine-grained sediment is present in drift complexes and isolated drifts. A small patch of fine-grained sediment slumped down one of the drift faces during the course of the Viking mission. Otherwise, no other morphological changes unrelated to spacecraft activity have been observed.

Binder, A. B.↗

NASA NTRS2013

Building a 2.5D Digital Elevation Model from 2D Imagery

When projecting imagery into a georeferenced coordinate frame, one needs to have some model of the geographical region that is being projected to. This model can sometimes be a simple geometrical curve, such as an ellipse or even a plane. However, to obtain accurate projections, one needs to have a more sophisticated model that encodes the undulations in the terrain including things like mountains, valleys, and even manmade structures. The product that is often used for this purpose is a Digital Elevation Model (DEM). The technology presented here generates a high-quality DEM from a collection of 2D images taken from multiple viewpoints, plus pose data for each of the images and a camera model for the sensor. The technology assumes that the images are all of the same region of the environment. The pose data for each image is used as an initial estimate of the geometric relationship between the images, but the pose data is often noisy and not of sufficient quality to build a high-quality DEM. Therefore, the source imagery is passed through a feature-tracking algorithm and multi-plane-homography algorithm, which refine the geometric transforms between images. The images and their refined poses are then passed to a stereo algorithm, which generates dense 3D data for each image in the sequence. The 3D data from each image is then placed into a consistent coordinate frame and passed to a routine that divides the coordinate frame into a number of cells. The 3D points that fall into each cell are collected, and basic statistics are applied to determine the elevation of that cell. The result of this step is a DEM that is in an arbitrary coordinate frame. This DEM is then filtered and smoothed in order to remove small artifacts. The final step in the algorithm is to take the initial DEM and rotate and translate it to be in the world coordinate frame [such as UTM (Universal Transverse Mercator), MGRS (Military Grid Reference System), or geodetic] such that it can be saved in a standard DEM format and used for projection.

Padgett, Curtis W.↗

NASA NTRS1987

Cratering history of Miranda

The surface of the southern hemisphere of Miranda imaged by Voyager 2 is divisible into two general types of terrain: cratered terrain, characterized by numerous craters and undulating intercrater plains; and basins, circular to rectangular areas of complex morphology having large-scale albedo markings. To determine the relative ages of the terrains and the length of geological activity, crater-frequency data were compiled for various parts of the cratered terrain and basins. Crater-frequency data indicate that the cratered terrain is the oldest terrain on Miranda and that it was locally resurfaced.

Plescia, J. B.↗

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↗

NASA NTRS2005

Satellite Gravity Drilling the Earth

Analysis of satellite-measured gravity and topography can provide crust-to-core mass variation models for new insi@t on the geologic evolution of the Earth. The internal structure of the Earth is mostly constrained by seismic observations and geochemical considerations. We suggest that these constraints may be augmented by gravity drilling that interprets satellite altitude free-air gravity observations for boundary undulations of the internal density layers related to mass flow. The approach involves separating the free-air anomalies into terrain-correlated and -decorrelated components based on the correlation spectrum between the anomalies and the gravity effects of the terrain. The terrain-decorrelated gravity anomalies are largely devoid of the long wavelength interfering effects of the terrain gravity and thus provide enhanced constraints for modeling mass variations of the mantle and core. For the Earth, subcrustal interpretations of the terrain-decorrelated anomalies are constrained by radially stratified densities inferred from seismic observations. These anomalies, with frequencies that clearly decrease as the density contrasts deepen, facilitate mapping mass flow patterns related to the thermodynamic state and evolution of the Earth's interior.

vonFrese, R. R. B.↗

NASA NTRS1989

Progress in the development of high degree potential coefficient models

A natural extension of the recent satellite derived potential coefficient models is the development of high degree (maximum 180 or 360) expansions. Such expansions are based on the combination of the satellite derived models with terrestrial gravity data and satellite altimeter data. Such models are useful for more precise geoid undulation computations, for simulation studies involving different typed of future missions (e.g., gradiometry), and as reference fields for different types of gravimetric computations. The attention is to the effect of the terrain, ellipsoidal terms, and weighting. The basic methods used for the high degree solutions are reviewed. Various correction terms are described and recent models are discussed and compared.

Rapp, Richard H.↗

NASA NTRS2004

Topographic variations in chaos on Europa: Implications for diapiric formation

Disrupted terrain, or chaos, on Europa, might have formed through melting of a floating ice shell from a subsurface ocean [Cam et al., 1998; Greenberg et al., 19991, or breakup by diapirs rising from the warm lower portion of the ice shell [Head and Pappalardo, 1999; Collins et al., 20001. Each model makes specific and testable predictions for topographic expression within chaos and relative to surrounding terrains on local and regional scales. High-resolution stereo-controlled photoclinometric topography indicates that chaos topography, including the archetypal Conamara Chaos region, is uneven and commonly higher than surrounding plains by up to 250 m. Elevated and undulating topography is more consistent with diapiric uplift of deep material in a relatively thick ice shell, rather than melt-through and refreezing of regionally or globally thin ice by a subsurface ocean. Vertical and horizontal scales of topographic doming in Conamara Chaos are consistent with a total ice shell thickness >15 km. Contact between Europa's ocean and surface may most likely be indirectly via diapirism or convection.

Schenk, Paul M.↗

NASA NTRS1989

Geoid undulation computations at laser tracking stations

The accuracy of numerical computations of gravimetric undulations using recently proposed modifications of the classical Stokes formula is investigated. The basic formulations of the methods are outlined, and results from trial computations are presented in tables and graphs and compared with actual gravity data and/or GEOS-3/Seasat sea-surface heights. Although all of the methods gave similar results, the method of Sjoberg (1986) is recommended because of its superior theoretical precision. The importance of including terrain-corrected free-air anomalies in the computations is indicated.

Despotakis, Vasilios K.↗

NASA NTRSDate not supplied

Large Impact Features on Icy Galilean Satellites: Implications for Ice Shell Thickness and Habitability.

Nowhere in the solar system are impact morphologies observed in greater variety than on the icy Galilean satellites. This is very likely a consequence of the structural and thermal state of the crust at the time of impact, and perhaps impact velocity. We have conducted a multi-disciplinary investigation to study how these features formed. The particular combination of geophysical factors and impactor characteristics that is shared by these satellites is likely responsible for these features. We have derived Digital Terrain Models for a number of these features, which have been used as a tool for producing facies maps. Impact features on Ganymede and Callisto are relatable to impact features on Europa, with implications for its ice shell history. We have identified two broad classes of these impact features: (a) Crater forms, which variously include pits, central domes, and crater rims; and (b) Palimpsests (including pene-palimpsests), which all have smooth enclosed central plains, an extensive outer undulating plains unit, concentric arcuate ridges(in the case of pene-palimpsests), and no recognizable rim. The very large, measured volume of the undulating plains unit of the pene-palimpsest Buto, Ganymede, substantially exceeds the amount of target material that could have been both melted and excavated by the impact event itself. Therefore, we conclude that the undulating plains material was derived from a fluid or “slushy” layer in the near-surface target at the time of impact. The recognition of undulating plains as the dominant unit in Memphis and Nidaba, two other palimpsests on Ganymede that we have mapped(which display highly variable crater counts, with Buto being the least cratered),leads us to a working hypothesis that these plains only form where and when the target has substantial near surface fluid or “slush.” By extension, all other impact features on Ganymede and Callisto, such as those with central pits and central domes, formed in targets with no pre-existing, or at most inconsequential, amounts of fluid or “slush.” Supporting this conclusion, modeling by members of our group indicates that the present topography of impact features with central pits and domes can be largely explained by the behavior of ice alone, with no or little contribution from fluids. Our study supports explanations for the formation and final appearance of palimpsests (and pene-palimpsests) that are entirely applicable to this feature class, and sharply distinct from explanations for other impact features (crater forms) on Ganymede and Callisto.

Jeffrey M Moore↗

NASA NTRS1988

Electrical structure and its implication across the lower- and upper-crustal settings of South India

Measurements of a large scale MMA experiment covering both the granulite and greenstone terrains of Archeans in the southern part of India is re-visited and re-analyzed. The induced field variations contain the signatures of crustal and subcrustal electrical conductivities, although substantially distorted by the sea-land interfaces and cenozoic sediments. However, through a selection of some reconnaissance profiles and temporal variations, an attempt is made to deduce whether: (1) significant differences exist between the electrical structures of the high and low grade complexes (i.e., if the electrical conductivity of the lower crust is due to minerological composition or is intrinsic to the positioning at depths greater than 15 km); (2) the probable seaward extension of the continental crust and its transition to oceanic type may also contribute (through intracrustal DC-like telluric sheets) to the induction field in addition to or rather than the sharply localized zones; (3) the observed parameters are indicative of a formal anisotropy and/or undulations in the deep crust; and (4) the postulate of relatively hotter Indian shield is reflected particularly with regard to differential metamorphism. In the last case, the crust-mantle coupling in this region - unlike other similar areas - seems to be markedly affected by the evolution of Ne-plate velocity field.

Raval, U.↗