A review of global satellite-derived snow products

Snow cover over the Northern Hemisphere plays a crucial role in the Earth’s hydrology and surface energy balance, and modulates feedbacks that control variations of global climate. While many of these variations are associated with exchanges of energy and mass between the land surface and the atmosphere, other expected changes are likely to propagate downstream and affect oceanic processes in coastal zones. For example, a large component of the freshwater flux into the Arctic Ocean comes from snow melt. The timing and magnitude of this flux affects biological and thermodynamic processes in the Arctic Ocean, and potentially across the globe through their impact on North Atlantic Deep Water formation.     

Variations in polar rain flux according to IMF geometries observed by STSAT-1

We examined polar rain flux observed by STSAT-1 in the northern polar cap and compared it with solar wind parameters. We found that the differential energy spectrum of polar rain was similar to that of the solar wind for the energy range 100 eV – 1 keV, although we cannot rule out the possibility of a small amount of acceleration. On the other hand, the low-energy component of the solar wind showed no correlation and, naturally, the solar wind density had only a weak correlation with the polar rain flux. Polar rain flux in the northern hemisphere is most significant for the condition of the interplanetary magnetic field components Bz < 0, Bx < 0, and By > 0, and in this case it correlated well with the magnitude of By and Bz. For other interplanetary magnetic field conditions, the correlation was insignificant. The results are consistent with those reported previously.     

X-ray Spectroscopy of Astrophysical Dust

High spectral resolution X-ray instruments on powerful X-ray satellites (e.g. Chandra, XMM-Newton) pointed through dust and gas at bright black holes and neutron stars can be used to study dust and intervening material in unique ways. With the new subfield of Condensed Matter Astrophysics as its goal, I will discuss current efforts to combine techniques and knowledge from condensed matter physics and astrophysics to determine the species-specific quantity and composition of interstellar gas and dust in the ISM and ionized environments. Prospects for improving on this work in future X-ray missions with higher throughput and spectral resolution are also presented in the context of spectral resolution goals for gratings and calorimeters.     

A Novel Feedforward Compensation Canceling Input Filter-Regulator I nteraction

The interaction between the input filter and the control loop of switching regulators often results in detrimental effects, such as loop instability, degradation of transient response, and audiosusceptibility, etc. The concept of pole-zero cancellation is employed to mitigate some of these detrimental effects and is implemented using a novel feedforward loop, in addition to existing feedback loops of a buck regulator. Experimental results are presented which show excellent correlation with theory.     

The FLUKA code for space applications: recent developments.

The FLUKA Monte Carlo transport code is widely used for fundamental research, radioprotection and dosimetry, hybrid nuclear energy system and cosmic ray calculations. The validity of its physical models has been benchmarked against a variety of experimental data over a wide range of energies, ranging from accelerator data to cosmic ray showers in the earth atmosphere. The code is presently undergoing several developments in order to better fit the needs of space applications. The generation of particle spectra according to up-to-date cosmic ray data as well as the effect of the solar and geomagnetic modulation have been implemented and already successfully applied to a variety of problems. The implementation of suitable models for heavy ion nuclear interactions has reached an operational stage. At medium/high energy FLUKA is using the DPMJET model. The major task of incorporating heavy ion interactions from a few GeV/n down to the threshold for inelastic collisions is also progressing and promising results have been obtained using a modified version of the RQMD-2.4 code. This interim solution is now fully operational, while waiting for the development of new models based on the FLUKA hadron-nucleus interaction code, a newly developed QMD code, and the implementation of the Boltzmann master equation theory for low energy ion interactions.     

Effects of a Finite-Width Decision Threshold on Binary CPSK and FSK Communication Systems

The function of the receiver in a binary digital communication system is to make a binary (?space?, ?mark? or ?"0?, ?1?) decision by comparing the signal values from the mark and space filters (or correlators) at known successive time intervals (?bit? or ?baud? time intervals). When the signal value out of the mark filter is greater than that out of the space filter, it is decided that mark or 1 is transmitted, and vice versa. It is of fundamental importance to know the exact instant of time at which the two filter outputs are to be compared. This is the problem of synchronization between the transmitter and the receiver. In this paper, we assume a system that is perfectly synchronized. In a practical system, the difference between the two filter outputs must differ from a threshold by some finite amount in order to cause the device to respond reliably. The examination of the effects of this dead zone (finite-width decision threshold) on digital transmission systems is of important practical interest. Its effects on binary differentially coherent phase-shift-keying, and m-level phase-shift-keying systems have been investigated previously. In this paper we consider its effects on binary coherent phase-shift-keying (CPSK), coherent orthogonal (CFSK), and noncoherent orthogonal (NCFSK) systems. The probability of bit error and the channel capacity of each system is obtained in terms of the dead zone threshold.     

Meteorological variations in the middle clouds of Venus from VEGA balloon in situ measurements

Instruments aboard the gondolas of the two VEGA balloons obtained in situ measurements of pressure, temperature, vertical velocity relative to the balloon, cloud particle backscatter, lightning and the ambient light level. Atmospheric motions at the balloon float altitudes were also determined from Earth-based tracking results. To illustrate the history of the balloon flights and to facilitate comparisons between some of the different observed quantities, measurements of pressure, temperature and backscatter are presented as time series for the entire lifetime of each balloon. Both long and short period variations have been detected. In addition, the environmental entropy encountered by each balloon will be discussed.     

NASA Automation and Robotics Technology Program

This paper presents an overview of NASA's Automation and Robotics (A&R) technology development program, covering its history, objectives, organization and content. This program is being carried out by the Office of Aeronautics and Space Technology (OAST) which has the responsibility to provide long range, high risk aerospace technology.     

Advanced Technologies Demonstrated by the Miniature Integrated Camera and Spectrometer (MICAS) Aboard Deep Space 1

MICAS is an integrated multi-channel instrument that includes an ultraviolet imaging spectrometer (80–185 nm), two high-resolution visible imagers (10–20 μrad/pixel, 400–900 nm), and a short-wavelength infrared imaging spectrometer (1250–2600 nm). The wavelength ranges were chosen to maximize the science data that could be collected using existing semiconductor technologies and avoiding the need for multi-octave spectrometers. It was flown on DS1 to validate technologies derived from the development of PICS (Planetary Imaging Camera Spectrometer). These technologies provided a novel systems approach enabling the miniaturization and integration of four instruments into one entity, spanning a wavelength range from the UV to IR, and from ambient to cryogenic temperatures with optical performance at a fraction of a wavelength. The specific technologies incorporated were: a built-in fly-by sequence; lightweight and ultra-stable, monolithic silicon-carbide construction, which enabled room-temperature alignment for cryogenic (85–140 K) performance, and provided superb optical performance and immunity to thermal distortion; diffraction-limited, shared optics operating from 80 to 2600 nm; advanced detector technologies for the UV, visible and short-wavelength IR; high-performance thermal radiators coupled directly to the short-wave infrared (SWIR) detector optical bench, providing an instrument with a mass less than 10 kg, instrument power less than 10 W, and total instrument cost of less than ten million dollars. The design allows the wavelength range to be extended by at least an octave at the short wavelength end and to ∼50 microns at the long wavelength end. Testing of the completed instrument demonstrated excellent optical performance down to 77 K, which would enable a greatly reduced background for longer wavelength detectors. During the Deep Space 1 Mission, MICAS successfully collected images and spectra for asteroid 9969 Braille, Mars, and comet 19/P Borrelly. The Borrelly encounter was a scientific hallmark providing the first clear, high resolution images and excellent, short-wavelength infrared spectra of the surface of an active comet’s nucleus.