Engineering topics
Publications and source records attributed to Harris, I..
The two GRACE (Gravity Recovery and Climate Experiment) spacecraft were launched into a near polar circular orbit around the earth in March of 2002. The two spacecraft serve as test masses to measure the Earth's gravitational field.
A science-quality space GPS receiver is being studied for the Primary Atomic Reference Clock in Space (PARCS) mission.
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This paper will describe the design and on-orbit performance of the GRACE Instrument Processing Unit (IPU) that integrates most of the critical science functions required by the GRACE mission to perform its gravity science and atmospheric radio occultation tasks.
We present a technique for converting real-time total electron content (TEC) measurements into gridded vertical delay corrections at the GPS L***sub***1 frequency, which will be broadcast to users every 5 min via geosynchronous satellite. Users will convert these delays to slant corrections for their own particular lines of sight to GPS satellites. To preserve user safety, estimates of the error in the user delay corrections will also be broadcast.
A database for Earth is now being created as the result of the Shuttle Radar Topography Mission (SRTM) during a 11 day Shuttle Endeavour flight in February.
The Federal Aviation Administration (FAA) is implementing a satellite-based navigation system for aircraft using the Global Positioning System (GPS).
The accuracy of single-frequency ocean altimeters benefits from calibration of the total electron content (TEC) of the ionosphere below the satellite.
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Explore the source record for details and available documents.
Explore the source record for details and available documents.
Explore the source record for details and available documents.
The ionospheric storm evolution process was monitored during the January 10, 1997 magnetic cloud event, through measurements of the inonospheric total electron content (TEC) from 150 GPS stations. The first significant response of the inonospheric TEC to the geomagnetic storm was at 0300 UT as an auroral/subauroral enhancement around the Alaskan evening sector.
Based on modeling some interactions between the middle atmosphere and thermosphere are presented. The interactions studied include the thermospheric circulations driven by radiative and auroral heating affecting the O concentration and temperature of the upper mesosphere through the exchange of chemical energy. Considering Kellog's mechanism, an interaction between the mesosphere and thermosphere that is driven by Joule heating is discussed.
A spectral model with spherical harmonics and Fourier components that can simulate atmospheric perturbations in the global geometry of a multiconstituent atmosphere is presented. The boundaries are the planetary surface where the transport velocities vanish and the exobase where molecular heat conduction and viscosity dominate. The time consuming integration of the conservation equations is reduced to computing the transfer function (TF) which describes the dynamic properties of the medium divorced from the complexities in the temporal and horizontal variations of the excitation source. Given the TF, the atmospheric response to a chosen source distribution is then obtained in short order. Theoretical studies are presented to illuminate some properties of gravity waves on earth, Venus and Mars.
The latest Voyager observations have shown large zonal velocities in Neptune's atmosphere, with some indication of alternating jets. Similar wind velocities have also been observed on Venus and are characteristic of planetary atmospheres in general, which is remarkable considering that the available solar or internal heating varies by more than a factor of 1000. A simplified model of the planetary circulation which provides some qualitative understanding is discussed. The basic assumption is that the source driving the circulation is also generating the dissipating eddies which are simulated by diffusion. Thus, the magnitude and structure of the zonal circulation are independent both of the source and the dissipation rate. The zonal velocities are related to the speed of sound and are of comparable magnitude in different atmospheres; although the available heating varies by a large factor, and the planetary parameters vary over a wide range. The alternating jets are described by a convective eigenmode which develops when energy transport out of the planetary interior is important, as is the case on Jupiter, Neptune, and Saturn.
This paper presents some numerical experiments performed with the TFM to study the various wave components excited in the auroral regions that propagate through the thermosphere and lower atmosphere, and to demonstrate the properties of realistic source geometries. The model is applied to the interpretation of satellite measurements, and gravity waves seen in the thermosphere of Venus are discussed. Gravity waves are prominent in the terrestrial thermosphere polar region and can be excited by perturbations in Joule heating and Lorentz force due to magnetospheric processes. Observations from the Dynamics Explorer-2 satellite are used to illustrate the complexity of the phenomenon and to review the TFM that is utilized.
A theoretical multiconstituent model (including O, N2, and O2) which describes the interactions between neutral winds, dynamo electric fields, and ion drifts is used to interpret observations that revealed a dominance of the fundamental diurnal tide in the upper thermosphere and at equatorial latitudes, and its effect on the thermospheric circulation. The model is shown to reproduce reasonably well the magnitudes of the neutral winds, ion drift velocities, and the ratio between the two. A solution for the neutral winds in which the dynamo electric field is forced to zero shows that the dynamo-induced ion drift is very important in accelerating the neutral atmosphere at higher altitudes. The dynamo interaction primarily affects the curl component of the field; its effect on the temperature and density perturbations is small.