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At least 1,027 records · Page 57

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NASA NTRS2015

Experimental and Computational Sonic Boom Assessment of Boeing N+2 Low Boom Models

Near-field pressure signatures were measured and computational predictions made for several sonic boom models representing Boeing's Quiet Experimental Validation Concept (QEVC) supersonic transport, as well as three axisymmetric calibration models. Boeing developed the QEVC under a NASA Research Announcement (NRA) contract for Experimental Systems Validations for N+2 Supersonic Commercial Transport Aircraft, which was led by the NASA High Speed Project under the Fundamental Aeronautics Program. The concept was designed to address environmental and performance goals given in the NRA, specifically for low sonic boom loudness levels and high cruise efficiency, for an aircraft anticipated to enter service in the 2020 timeframe. Wind tunnel tests were conducted on the aircraft and calibration models during Phases I and II of the NRA contract from 2011 to 2013 in the NASA Ames 9- by 7-Foot and NASA Glenn 8- by 6-Foot Supersonic Wind Tunnels. Sonic boom pressure signatures were acquired primarily at Mach 1.6 and 1.8, and force and moment data were acquired from Mach 0.8 to 1.8. The sonic boom test data were obtained using a 2-in. flat-top pressure rail and a 14-in. round-top tapered "reflection factor 1" (RF1) pressure rail. Both rails capture an entire pressure signature in one data point, and successive signatures at varying positions along or above the rail were used to improve data quality through spatial averaging. The sonic boom data obtained by the rails were validated with high-fidelity numerical simulations of off-body pressures using the CFD codes USM3D, Cart3D, and OVERFLOW. The test results from the RF1 rail showed good agreement between the computational and experimental data when a variety of testing techniques including spatial averaging of a series of pressure signatures were employed, however, reflections off the 2-in. flat-top rail caused distortions in the signatures that did not agree with the CFD predictions. The 9 x 7 and 8 x 6 wind tunnels generally produced comparable data.

pressure signature↗

NASA NTRS1973

Identification of phenological stages and vegetative types for land use classification

The author has identified the following significant results. Multispectral reflectance signatures have been obtained from computer printouts from scene 1049-20505. Those signatures have been grouped for 13 dominant physical features in the Matanuska Susitna Valley area of Alaska. The derived signatures will be validated and tested by requesting another symbol-coded computer printout for the same area. It is expected that ERTS-1 imagery collected during late autumn and early spring will provide separations of signatures that are confounded in the 1049-20505 scene. Separating bogs and forests should be much improved when either snow covered or when grasses are brown. Photographs have been made of projections on the color additive viewer, each scene being projected with six different filter combinations. The products will be analyzed and those best suited used for producing color transparencies at a scale of 1:250,000 for overlaying on standard quadrangle maps. Color prints will be processed for use in the field. From digital MSS signatures derived to date, identification has been made of which bands are the most powerful for automated classification of dominant physical features. It has been found that separations among density ranges increase with longer wavelengths. Deriving MSS digital signatures has proven valuable to both digital and visual processing of ERTS-1 data.

Branton, C. I.↗

NASA NTRS1980

A study of the sonic-boom characteristics of a blunt body at a Mach number of 6

An experimental and analytical study of the sonic boom static pressure signatures generated by a blunt body at mach 6 has shown that finite difference computer programs can be used to give reasonable estimates of the signatures. The calculated near field static pressure signature was extrapolated to the far field by a program using the method of characteristics. A comparison of this extrapolated signature with the signature predicted by far field sonic boom theory (linearized) shows that peak overpressures are about the same, at least up to mach, but the far field theory overestimates the length of the signature.

Ashby, G. C., Jr.↗

NASA NTRS1983

The Mimas ghost revisited: An analysis of the electron flux and electron microsignatures observed in the vicinity of Mimas at Saturn

An analysis of the electron absorption signature observed by the Cosmic Ray System (CRS) on Voyage 2 near the orbit of Mimas is presented. We find that these observations cannot be explained as the absorption signature of Mimas. Combing Pioneer 11 and Voyager 2 measurements of the electron flux at Mimas's orbit (L=3.1), we find an electron spectrum where most of the flux above approx 100 keV is concentrated near 1 to 3 MeV. The expected Mimas absorption signature is calculated from this spectrum neglecting radial diffusion. A lower limit on the diffusion coefficient for MeV electrons is obtained. With a diffusion coefficient this large, both the Voyager 2 and the Pioneer 11 small-scale electron absorption signature observations in Mimas's orbit are enigmatic. Thus we refer to the mechanism for producing these signatures as the Mimas ghost. A cloud of material in orbit with Mimas may account for the observed electron signature if the cloud is at least 1% opaque to electrons across a region extending over a few hundred kilometers.

Chenette, D. L.↗

NASA NTRS1992

Effect of sonic boom asymmetry on subjective loudness

The NASA Langley Research Center's sonic boom apparatus was used in an experimental study to quantify subjective loudness response to a wide range of asymmetrical N-wave sonic boom signatures. Results were used to assess the relative performance of several metrics as loudness estimators for asymmetrical signatures and to quantify in detail the effects on subjective loudness of varying both the degree and direction of signature loudness asymmetry. Findings of the study indicated that Perceived Level (Steven's Mark 7) and A-weighted sound exposure level were the best metrics for quantifying asymmetrical boom loudness. Asymmetrical signatures were generally rated as being less loud than symmetrical signatures of equivalent Perceived Level. The magnitude of the loudness reductions increased as the degree of boom asymmetry increased, and depended upon the direction of asymmetry. These loudness reductions were not accounted for by any of the metrics. Corrections were determined for use in adjusting calculated Perceived Level values to account for these reductions. It was also demonstrated that the subjects generally incorporated the loudness components of the complete signatures when making their subjective judgments.

Leatherwood, Jack D.↗

NASA NTRS1999

Mesoscale Numerical Investigations of Air Traffic Emissions over the North Atlantic during SONEX Flight 8: A Case Study

Chemical data from flight 8 of NASA's Subsonic Assessment (SASS) Ozone and Nitrogen Oxide Experiment (SONEX) exhibited signatures consistent with aircraft emissions, stratospheric air, and surface-based pollution. These signatures are examined in detail, focussing on the broad aircraft emission signatures that are several hundred kilometers in length. A mesoscale meteorological model provides high resolution wind data that are used to calculate backward trajectories arriving at locations along the flight track. These trajectories are compared to aircraft locations in the North Atlantic Flight Corridor over a 27-33 hour period. Time series of flight level NO and the number of trajectory/aircraft encounters within the NAFC show excellent agreement. Trajectories arriving within the stratospheric and surface-based pollution regions are found to experience very few aircraft encounters. Conversely, there are many trajectory/aircraft encounters within the two chemical signatures corresponding to aircraft emissions. Even many detailed fluctuations of NO within the two aircraft signature regions correspond to similar fluctuations in aircraft encountered during the previous 27-33 hours. Results indicate that high resolution meteorological modeling, when coupled with detailed aircraft location data, is useful for understanding chemical signatures from aircraft emissions at scales of several hundred kilometers.

Bieberbach, George, Jr.↗

NASA NTRS1999

Boom Softening and Nacelle Integration on an Arrow-Wing High-Speed Civil Transport Concept

During the last cycle of concept design and wind-tunnel testing, the goal of the low-boom- shaped HSCT concepts (the B-935, the LB-16, and the LB- 1 8) was to meet mission requirements and generate shaped, ground-level pressure signatures with nose shock strengths of 1.0 psf or less. The wind-tunnel tests of these concepts produced results that were partially successful and encouraging although not fully up to expectations. In spite of this, however, these conceptual designs were overly optimistic and not acceptable because: the wing planforms had excessive area; the wing structural aspect ratio was too high; one concept had aft-fuselage rather than under-the-wing engines; and the gross takeoff weights were unrealistically low because of engines that were early, high-tech versions of later, revised, more-realistic engines. The need for reducing the ground-level overpressure shock strengths still existed; a need to be met within more restrictive guidelines of mission performance and gross takeoff weight limitations. Therefore, it was decided that the next conceptual design cycle would focus on decreased nose shock strengths, "boom softening," in the signatures of the Boeing and the McDonnell Douglas baseline concepts rather than low-boom concepts with shaped-signature designs. Overly-optimistic results were not the only problem with these low-sonic-boom concepts. Papers given at the 1994 Sonic-Boom Workshop had demonstrated that the problem of successful nacelle integration on HSCT concepts had only been partially solved. Wind-tunnel pressure signature data, from the HSCT-11B (a.k.a. the LB-18) wind-tunnel model, showed that the Langley HSCT design and analysis method had been successful in reducing the nacelle-volume disturbances in the flow field. This was due.to the engine nacelles mounted behind the wing trailing-edge on the aft fuselage so that no nacelle-wing interference-lift flow-field disturbances were generated. While acceptable from a sonic-boom research point of view, this concept was unacceptable from several practical and structural considerations. Preliminary wind-tunnel pressure signature data from the LB-16 wind-tunnel model, which had the engine nacelles mounted under the wings (the usual location), indicated that the application of the Langley nacelle-integration method had been only partially successful in the reduction of the nacelle-volume with nacelle-wing interference-lift pressure disturbances. So, "boom softening" had to also address the task of successful integration of the engine nacelles, with the engines in the required under-the-wing location. Unless this problem was solved, low-sonic-boom and low-drag modifications to the wing planform, the airfoil shape, and the fuselage longitudinal area distribution could be nullified if the nacelle disturbances added increments to the nose-shock strengths that were removed through component tailoring. In this paper, an arrow-wing boom-softened HSC7 concept which incorporated modifications to a baseline McDonnell Douglas concept is discussed. The analysis of the concept's characteristics will include estimates of weight, center of gravity, takeoff field length, mission range, and predictions of its ground-level sonic-boom pressure signature. Additional modifications which enhanced the softened-boom performance of this concept are also described as well as estimates of the performance penalties induced by these modifications.

Mack, Robert J.↗

NASA NTRS1999

Sonic Boom Prediction and Minimization of the Douglas Reference OPT5 Configuration

Conventional CFD methods and grids do not yield adequate resolution of the complex shock flow pattern generated by a real aircraft geometry. As a result, a unique grid topology and supersonic flow solver was developed at Northrop Grumman based on the characteristic behavior of supersonic wave patterns emanating from the aircraft. Using this approach, it was possible to compute flow fields with adequate resolution several body lengths below the aircraft. In this region, three-dimensional effects are diminished and conventional two-dimensional modified linear theory (MLT) can be applied to estimate ground pressure signatures or sonic booms. To accommodate real aircraft geometries and alleviate the burdensome grid generation task, an implicit marching multi-block, multi-grid finite-volume Euler code was developed as the basis for the sonic boom prediction methodology. The Thomas two-dimensional extrapolation method is built into the Euler code so that ground signatures can be obtained quickly and efficiently with minimum computational effort suitable to the aircraft design environment. The loudness levels of these signatures can then be determined using a NASA generated noise code. Since the Euler code is a three-dimensional flow field solver, the complete circumferential region below the aircraft is computed. The extrapolation of all this field data from a cylinder of constant radius leads to the definition of the entire boom corridor occurring directly below and off to the side of the aircraft's flight path yielding an estimate for the entire noise "annoyance" corridor in miles as well as its magnitude. An automated multidisciplinary sonic boom design optimization software system was developed during the latter part of HSR Phase 1. Using this system, it was found that sonic boom signatures could be reduced through optimization of a variety of geometric aircraft parameters. This system uses a gradient based nonlinear optimizer as the driver in conjunction with a computationally efficient Euler CFD solver (NIIM3DSB) for computing the three-dimensional near-field characteristics of the aircraft. The intent of the design system is to identify and optimize geometric design variables that have a beneficial impact on the ground sonic boom. The system uses a simple wave drag data format to specify the aircraft geometry. The geometry is internally enhanced and analytic methods are used to generate marching grids suitable for the multi-block Euler solver. The Thomas extrapolation method is integrated into this system, and hence, the aircraft's centerline ground sonic boom signature is also automatically computed for a specified cruise altitude and yields the parameters necessary to evaluate the design function. The entire design system has been automated since the gradient based optimization software requires many flow analyses in order to obtain the required sensitivity derivatives for each design variable in order to converge on an optimal solution. Hence, once the problem is defined which includes defining the objective function and geometric and aerodynamic constraints, the system will automatically regenerate the perturbed geometry, the necessary grids, the Euler solution, and finally the ground sonic boom signature at the request of the optimizer.

Siclari, Michael J.↗

NASA NTRS2009

Design of Experiments for Both Experimental and Analytical Study of Exhaust Plume Effects on Sonic Boom

Computational fluid dynamics (CFD) analysis has been performed to study the plume effects on sonic boom signature for isolated nozzle configurations. The objectives of these analyses were to provide comparison to past work using modern CFD analysis tools, to investigate the differences of high aspect ratio nozzles to circular (axisymmetric) nozzles, and to report the effects of under expanded nozzle operation on boom signature. CFD analysis was used to address the plume effects on sonic boom signature from a baseline exhaust nozzle. Nearfield pressure signatures were collected for nozzle pressure ratios (NPRs) between 6 and 10. A computer code was used to extrapolate these signatures to a ground-observed sonic boom N-wave. Trends show that there is a reduction in sonic boom N-wave signature as NPR is increased from 6 to 10. As low boom designs are developed and improved, there will be a need for understanding the interaction between the aircraft boat tail shocks and the exhaust nozzle plume. These CFD analyses will provide a baseline study for future analysis efforts. For further study, a design of experiments has been conducted to develop a hybrid method where both CFD and small scale wind tunnel testing will validate the observed trends. The CFD and testing will be used to screen a number of factors which are important to low boom propulsion integration, including boat tail angle, nozzle geometry, and the effect of spacing and stagger on nozzle pairs. To design the wind tunnel experiment, CFD was instrumental in developing a model which would provide adequate space to observe the nozzle and boat tail shock structure without interference from the wind tunnel walls.

Castner, Raymond S.↗

NASA NTRS2016

Proteomic Assessment of Fluid Shifts and Association with Visual Impairment and Intracranial Pressure in Twin Astronauts

BACKGROUND: Astronauts participating in long duration space missions are at an increased risk of physiological disruptions. The development of visual impairment and intracranial pressure (VIIP) syndrome is one of the leading health concerns for crew members on long-duration space missions; microgravity-induced fluid shifts and chronic elevated cabin CO2 may be contributing factors. By studying physiological and molecular changes in one identical twin during his 1-year ISS mission and his ground-based co-twin, this work extends a current NASA-funded investigation to assess space flight induced "Fluid Shifts" in association with the development of VIIP. This twin study uniquely integrates physiological and -omic signatures to further our understanding of the molecular mechanisms underlying space flight-induced VIIP. We are: (i) conducting longitudinal proteomic assessments of plasma to identify fluid regulation-related molecular pathways altered by long-term space flight; and (ii) integrating physiological and proteomic data with genomic data to understand the genomic mechanism by which these proteomic signatures are regulated. PURPOSE: We are exploring proteomic signatures and genomic mechanisms underlying space flight-induced VIIP symptoms with the future goal of developing early biomarkers to detect and monitor the progression of VIIP. This study is first to employ a male monozygous twin pair to systematically determine the impact of fluid distribution in microgravity, integrating a comprehensive set of structural and functional measures with proteomic, metabolomic and genomic data. This project has a broader impact on Earth-based clinical areas, such as traumatic brain injury-induced elevations of intracranial pressure, hydrocephalus, and glaucoma. HYPOTHESIS: We predict that the space-flown twin will experience a space flight-induced alteration in proteins and peptides related to fluid balance, fluid control and brain injury as compared to his pre-flight protein/peptide signatures. Conversely, the trajectory of these protein signatures will remain relatively constant in his ground based co-twin. METHODS: We are using proteomic and standard immunoelectrophoresis techniques to delineate the change in protein signatures throughout the course of a long duration space flight in relation to the development of VIIP. We are also applying a novel cell-based metaboloic organ system assay ("Organs on a Plate") to address how these circulating biomarkers affect physiological processes at the cellular and organ level which could result in VIIP symptoms. These molecular data will be correlated with physiological measures (eg. extra and intracellular fluid volume, vascular filling/flow patterns, MRI, and Optic Coherence Tomography. DISCUSSION: Pre- and in-flight data collection is in progress for the space-flown twin, and similar data have been obtained from the ground-based twin. Biosamples will be batch processed when received from ISS after the conclusion of the 1-year mission. Omic and Physiological measures from the twin astronauts will be compared to similar data being collected on twin subjects who participated in simulated microgravity study. bed rest study.

Rana, Brinda K.↗

NASA NTRS2022

USM3D Simulations for the Third AIAA Sonic Boom Prediction Workshop

The NASA USM3D flow solver was used to compute test cases for the Third AIAA Sonic Boom Prediction Workshop (SBPW3). The test cases included a nearfield biconvex shock-plume interaction wind tunnel model and the C608 Low Boom Flight Demonstrator. Numerical simulations were conducted on the mixed-element and tetrahedral grids provided by the workshop committee, as well as a family of grids generated by an in-house approach known as BoomGrid. The nearfield pressure signatures were extracted and propagated to the ground, and the perceived loudness levels on the ground were computed. The USM3D nearfield pressure signatures, corresponding ground signatures, and loudness levels on the ground were compared with that of mean values from other workshop participants. The effect of three flux-limiters on the accuracy of nearfield pressure signature prediction was investigated and results were compared with that of mean values from other workshop participants. The effect of using wall-function models for predicting nearfield pressure signatures was also evaluated. Results showed that the overpressure signatures extracted from the wall-modeled simulations and the wall-resolved simulations are in good agreement. The use of wall functions (wall-modeled simulations) allowed for approximately 23% savings in the time to solution and yielded comparable perceived loudness levels on the ground to the wall-resolved Reynolds-averaged Navier Stokes simulations.

Supersonics↗

NASA NTRS2023

X-59 Sonic Boom Test Results from the NASA Glenn 8- by 6-Foot Supersonic Wind Tunnel

A wind tunnel test was conducted to investigate near-field sonic boom pressure signatures of the X-59 Low-Boom Flight Demonstrator aircraft. A 1.62%-scale model of the aircraft was fabricated for the wind tunnel test, which took place in the NASA Glenn 8- by 6-Foot Supersonic Wind Tunnel in September and October 2021. The model had provisions for being mounted by a swept blade strut that attached at top of model ahead of the inlet, or by a rear-entry sting that held the model at the location of the nacelle. The model had alternate parts for ±0.5° deflections of the flaps, ailerons, and stabilator, and ±1° deflections of the T-tail. Off-body static pressure measurements of the flow field below the model were made on a pressure rail which had 420 orifices along its tip. The model was positioned at various heights from the rail by vertical movement of the tunnel strut, and at various longitudinal stations relative to the rail by means of a linear actuator mounted between the wind tunnel strut and the balance. Spatial averaging of model pressure signatures acquired over a range of longitudinal positions reduced the effects of tunnel flow distortions and the interference of the rail flow field and shocks on the model pressure signatures. The test was run at approximate Mach numbers of 1.36, 1.4, and 1.47, and the model was set at various angles of attack and roll relative to the rail. Plots of the model signatures for representative variations of Mach number, model angles, control deflections, and height relative to the rail are provided throughout the report. Repeatability was generally very good and gave confidence in the quality of the measurements. The signatures measured at various heights from the rail provided insight into the aging of the model shocks as they propagated from 1.2 to 3 body lengths from the model. Off-track signatures up to 45° from centerline obtained by rolling the model gave indications of the shock flow fields across the width of the sonic boom carpet. The deflections of the various control surfaces allowed assessment of the boom sensitivity to the control surface movements.

Sonic boom↗

NASA NTRS2023

X-59 Sonic Boom Test Results from the NASA Glenn 8- by 6-Foot Supersonic Wind Tunnel

Sonic boom↗

NASA NTRS1973

A study of methods which predict supersonic flow fields from body geometry, distance, and Mach number

A study of seven methods for predicting flow-field pressure signatures from the parameters Mach number, body geometry, and field-path distance has been made. The methods included the method of characteristics, which served as a standard of comparison; a shock-capturing method; three Whitham theory methods; a modified characteristics method; and a bicharacteristics method. Results from each method were also compared with recently obtained wind-tunnel data for a cone-cylinder model at Mach numbers of 2.96 and 4.63 with ratios of radial distance to cone length of 2 and 5. The comparisons at a Mach number of 2.96 showed that signatures from all the methods correlated well with wind-tunnel data and with the signatures predicted by the method of characteristics. At a Mach number of 4.63, however, the agreement between the signatures obtained in the wind tunnel and those predicted by theory varied from good to poor, as did the agreement between the signatures obtained by the method of characteristics and the other six methods. It should be noted that these results and comparisons indicate pressure prediction capabilities only for the near-field flow about bodies of revolution.

Mack, R. J.↗

NASA NTRS1985

Correlation of predicted and measured sonic boom characteristics from the reentry of STS-1 orbiter

Characteristics from sonic boom pressure signatures recorded at 11 locations during reentry of the Space Shuttle Orbiter Columbia are correlated with characteristics of wind tunnel signatures extrapolated from flight altitudes for Mach numbers ranging from 1.23 to 5.87. The flight pressure signature were recorded by microphones positioned at two levels near the descent groundtrack along the California corridor. The wind tunnel signatures used in theoretical predictions were measured using a 0.0041-scale model Orbiter. The mean difference between all measured and predicted overpressures is 12 percent from measured levels. With one exception, the flight signatures are very similar to theoretical n-waves.

Garcia, F., Jr.↗

NASA NTRS1992

Computational/experimental analysis of three low sonic boom configurations with design modifications

The Euler code, designated AIRPLANE, which uses an unstructured tetrahedral mesh was used to compute near-field sonic boom pressure signatures on three modern low sonic boom configurations: the Mach 2, Mach 3, and Haglund models. The TEAM code which uses a multi-zoned structured grid was used to calculate pressure signatures for the Mach 2 model. The computational pressure signatures for the Mach 2 and Mach 3 models are compared with recent experimental data. The computed pressure signatures were extracted at distances less than one body length below the configuration and extrapolated to the experimental distance. The Mach 2 model was found to have larger overpressures off-ground-track than on-ground-track in both computational and experimental results. The correlations with the experiment were acceptable where the signatures were not contaminated by instrumentation and model-support hardware. AIRPLANE was used to study selected modifications to improve the overpressures of the Mach 2 model.

Cliff, Susan E.↗

NASA NTRS1992

Sonic boom prediction for the Langley Mach 2 low-boom configuration

Sonic boom pressure signatures and aerodynamic force data for the Langley Mach 2 low sonic boom configuration were computed using the TranAir full-potential code. A solution-adaptive Cartesian grid scheme is utilized to compute off-body flow field data. Computations were performed with and without nacelles at several angles of attack. Force and moment data were computed to measure nacelle effects on the aerodynamic characteristics and sonic boom footprints of the model. Pressure signatures were computed both on and off ground-track. Near-field pressure signature computations on ground-track were in good agreement with experimental data. Computed off ground-track signatures showed that maximum pressure peaks were located off ground-track and were significantly higher than the signatures on ground-track. Bow shocks from the nacelle inlets increased lift and drag, and also increased the magnitude of the maximum pressure both on and off ground-track.

Madson, Michael D.↗

NASA NTRS1993

Gravity investigation of the Manson impact structure, Iowa

The Manson crater, of probable Cretaceous/Tertiary age, is located in northwestern Iowa (center at 42 deg. 34.44 min N; 94 deg. 33.60 min W). A seismic reflection profile along an east west line across the crater and drill hole data indicate a crater about 35 km in diameter having the classic form for an impact crater, an uplifted central peak composed of uplifted Proterozoic crystalline bedrock, surrounded by a 'moat' filled with impact produced breccia and a ring graben zone composed of tilted fault blocks of the Proterozoic and Paleozoic country rocks. The structure has been significantly eroded. This geologic structure would be expected to produce a significant gravity signature and study of that signature would shed additional light on the details of the crater structure. A gravity study was undertaken to better resolve the crustal structure. The regional Bouguer gravity field is characterized by a southeastward decreasing field. To first order, the Bouguer gravity field can be understood in the context of the geology of the Precambrian basement. The high gravity at the southeast corner is associated with the mid-continent gravity high; the adjacent low to the northwest results from a basin containing low-density clastic sediments shed from the basement high. Modeling of a simple basin and adjacent high predicts much of the observed Bouguer gravity signature. A gravity signature due to structure associated with the Manson impact is not apparent in the Bouguer data. To resolve the gravity signature of the impact, a series of polynomial surfaces were fit to the Bouguer gravity field to isolate the small wavelength residual anomalies. The residual gravity obtained after subtracting a 5th- or 6th-order polynomial seems to remove most of the regional effects and isolate local anomalies. The pattern resolved in the residual gravity is one of a gravity high surrounded by gravity lows and in turn surrounded by isolated gravity highs. The central portion of the crater is characterized by two positive anomalies having amplitudes of about plus 4 mGal separated by a gentle saddle located approximately at the crater center.

Plescia, J. B.↗