Meteor44 Video Meteor Photometry

Meteor44 is a software system developed at MSFC for the calibration and analysis of video meteor data. The photometric range of the (8 bit) video data is extended from a visual magnitude range of from 8 to 3 to from 8 to −8 for both meteors and stellar images using saturation compensation. Camera and lens specific saturation compensation coefficients are derived from artificial variable star laboratory measurements. Saturation compensation significantly increases the number of meteors with measured intensity and improves the estimation of meteoroid mass distribution. Astrometry is automated to determine each image's plate coefficient using appropriate star catalogs. The images are simultaneously intensity calibrated from the contained stars to determine the photon sensitivity and the saturation level referenced above the atmosphere. The camera's spectral response is used to compensate for stellar color index and typical meteor spectra in order to report meteor light curves in traditional visual magnitude units. Recent efforts include improved camera calibration procedures and long focal length "streak" meteor photometry. Meteor44 has been used to analyze data from the 2001, 2002 and 2003 MSFC Leonid observational campaigns as well as several lesser showers.     

Determining a tilt in Titan’s north-south albedo asymmetry from Cassini images

Analysis of Titan’s hemispheric brightness asymmetry from mapped Cassini images reveals an axis of symmetry that is tilted with respect to the rotational axis of the solid body. Twenty images taken from 2004 through 2007 show a mean axial offset of 3.8 ± 0.9° relative to the solid body’s pole, directed 79 ± 24° to the west of the sub-solar longitude. These values are consistent with recent measurements of an implied atmospheric spin axis determined from isothermal mapping by [Achterberg, R.K., Conrath, B.J., Gierasch, P.J., Flasar, F.M., Nixon, C.A., 2008. Icarus 197, 549-555].     

Magnetic zones of Mars: Deformation‐controlled origin of magnetic anomalies

Abstract— Intense magnetic anomalies over Martian surface suggest preservation of large volumes of very old crust (>3 Gyr) that formed in the presence of a global magnetic field. The global distribution of the magnetic intensities observed above the Martian crust suggests a division into three zones. Zone 1 is where the magnetic signature is negligible or of relatively low intensity at Mars Global Surveyor (MGS) satellite mapping altitude (400 km). Zone 2 is the region of intermediate crustal magnetic amplitudes and zone 3 is where the highest magnetic intensities are measured. Crater demagnetization near zone 3 reveals the presence of rocks with both high magnetic intensity and coercivity. Magnetic analyses of terrestrial rocks show that compositional banding in orogenic zones significantly enhances both magnetic coercivity and thermal remanent magnetization (TRM) efficiency. Such enhancement offers a novel explanation for the anomalously large intensities inferred of magnetic sources on Mars. We propose that both large magnetic coercivity and intensity near the South Pole is indicative of the presence of a large degree of deformation. Associated compositional zoning creates conditions for large scale magnetic anisotropy allowing magnetic minerals to acquire magnetization more efficiently, thereby causing the distinct magnetic signatures in zone 3, expressed by intense magnetic anomalies. We use a simple model to verify the magnetic enhancement. We hypothesize that magnetically enhanced zone would reside over the down welling plume at the time of magnetization acquisition.     

Numerical simulations of the Mediterranean sea outflow: impact of the entrainment parameterization in an isopycnic coordinate ocean model

Gravity current entrainment is essential in determining the properties of the interior ocean water masses that result from marginal sea overflows. Although the individual entraining billows will be unresolvable in large-scale ocean models for the foreseeable future, some large-scale simulations are now being carried out that do resolve the intermediate scale environment which may control the rate of entrainment. Hallberg [Mon. Wea. Rev. 128 (2000) 1402] has recently developed an implicit diapycnal mixing scheme for isopycnic coordinate ocean models that includes the Richardson number dependent entrainment parameterization of Turner [J. Fluid Mech. 173 (1986) 431], and which may be capable of representing the gravity current evolution in large-scale ocean models. The present work uses realistic regional simulations with the Miami Isopycnic Coordinate Ocean Model (MICOM) to evaluate ability of this scheme to simulate the entrainment that is observed to occur in the bottom boundary currents downstream of the Mediterranean outflow. These simulations are strikingly similar to the observations, indicating that this scheme does produce realistic mixing between the Mediterranean outflow and the North Atlantic Central Water. Sensitivity studies identify the critical Richardson number below which vigorous entrainment occurs as a particularly important parameter. Some of these experiments also show meddies detaching from the Mediterranean undercurrent at locations that appear to be highly influenced by topographic features.     

MaxEnt power spectrum estimation using the Fourier transform for irregularly sampled data applied to a record of stellar luminosity

The principle of maximum entropy is applied to the spectral analysis of a data signal with general variance matrix and containing gaps in the record. The role of the entropic regularizer is to prevent one from overestimating structure in the spectrum when faced with imperfect data. Several arguments are presented suggesting that the arbitrary prefactor should not be introduced to the entropy term. The introduction of that factor is not required when a continuous Poisson distribution is used for the amplitude coefficients. We compare the formalism for when the variance of the data is known explicitly to that for when the variance is known only to lie in some finite range. The result of including the entropic measure factor is to suggest a spectrum consistent with the variance of the data which has less structure than that given by the forward transform. An application of the methodology to example data is demonstrated.     

The NASA Lunar Impact Monitoring Program

NASA’s Meteoroid Environment Office has implemented a program to monitor the Moon for meteoroid impacts from the Marshall Space Flight Center. Using off-the-shelf telescopes and video equipment, the Moon is monitored for as many as 10 nights per month, depending on weather. Custom software automatically detects flashes which are confirmed by a second telescope, photometrically calibrated using background stars, and published on a website for correlation with other observations. Hypervelocity impact tests at the Ames Vertical Gun Range facility have begun to determine the luminous efficiency and ejecta characteristics. The purpose of this research is to define the impact ejecta environment for use by lunar spacecraft designers of the Constellation manned lunar program. The observational techniques and preliminary results will be discussed. The U.S. Government's right to retain a non-exclusive, royalty-free license in and to any copyright is acknowledged.