Latitudinal Variation of the Underlying Heliospheric Magnetic Field Direction: Comparison of the Ulysses First and Second Orbits

We discuss the underlying direction of the heliospheric magnetic field measured by Ulysses in the latitude range 6° S-65° S by examining distributions of the magnetic field azimuthal angle with respect to the simple Parker spiral model. During the first Ulysses traversal of this latitude range in 1992–1994, while solar activity was declining, the shape of the distributions obtained at high latitudes in the fast solar wind differed from that at lower latitudes. In the present data set, obtained during rising solar activity, both field polarities are present at all latitudes and the peaks of the distributions agree with the predicted spiral direction to first approximation. However, compared to the first orbit, a significantly greater percentage of the observed field vectors have large deviations from the spiral direction. This revised version was published online in August 2006 with corrections to the Cover Date.     

A compact dopplergraph/magnetograph suitable for space-based measurements of solar oscillations and magnetic fields

A compact Dopplergraph/magnetograph placed in a continuous solar-viewing orbit will allow us to make major advancements in our understanding of solar internal structure and dynamics. An international program is currently being conducted at JPL and Mt. Wilson to develop such an instrument. By combining a unique magneto-optical resonance filter with CID and CCD cameras we have been able to obtain full- and partial-disk Dopplergrams and magnetograms. Time series of the velocity images are converted into k-ω power spectra which show clear- the solar nonradial p-mode oscillations. Magnetograms suitable for studying the long-term evolution of solar active regions have also been obtained with this instrument. A flight instrument based on this concept is being studied for possible inclusion in the SOHO mission.     

Ulysses charged particle measurements between 1 and 5 AU from the sun.

Proton fluxes obtained by two instruments carried on the ESA/NASA Ulysses spacecraft are reported for the period from launch in October 1990 till Jupiter encounter in February 1992. Proton energy ranges are 24-59, 71-99, 130-320, 320-2100 and > 2100 MeV. The Sun was very active during this period, the events of March 1991 being some of the largest of the solar cycle. The relationship between events on the Sun and the observed proton flux is discussed.     

Additional results on `reducing geometric dilution of precisionusing ridge regression'

R.J. Kelly (1990) presented preliminary results on the feasibility of using ridge regression to reduce the effects of geometric dilution of precision (GDOP) error inflation in position-fix navigation systems. Results indicate that the ridge technique will not reduce bias inflation due to the effects of GDOP in applications where bias-like measurement errors persist for time periods which greatly exceed the response time of an aircraft's guidance loop. This conclusion will preclude the use of ridge regression on navigation systems whose dominant error sources are bias-like. This applies in particular to the Global Positioning System (GPS) selective availability error source. All the simulation results given in Kelly's work are, however, valid for the conditions defined. Although ridge regression has not yielded a satisfactory solution to the general GDOP problem, it has illuminated the role that multicollinearity plays in navigation signal processors such as the Kalman filter. After a background discussion, bias inflation, initial position guess errors, ridge parameter selection methodology, and the recursive ridge filter, are discussed     

Satellites for the study of ocean primary productivity

Estimates of global marine primary productivity are currently based upon the ¹⁴C method for determining rates of plankton photosynthesis and upon the relatively sparse data available using shipboard sampling techniques. With recent advances in remote sensing and in multiplatform (ship, aircraft, and satellite) sampling strategies, it is now possible to significantly lower the variance in estimates of phytoplankton abundance and of population growth rates.Multiplatform sampling strategies are essential to assess the mean and variance of phytoplankton biomass on a regional or on a global basis. The relative errors associated with shipboard and satellite estimates of phytoplankton biomass and primary productivity, as well as the increased statistical accuracy now possible from the utilization of contemporaneous data from both sampling platforms, are discussed. It is shown that one of the more exciting and potentially useful aspects of oceanographic research today is our new ability to view large areas of the ocean synoptically.     

The identification of mesospheric frontal gravity-wave events at a mid-latitude site

Mesospheric frontal-type gravity waves are an uncommon type of wave disturbance that occurs in the mesospheric OH, Na, O₂, and O(¹S) nightglow. They are understood to be the result of gravity waves exhibiting various degrees of non-linear behavior. Despite their similar appearance in all-sky images, careful analysis reveals that there are at least two distinct types of frontal wave disturbances, each with completely different consequences in terms of vertical momentum transport and deposition. Therefore, a correct identification is important in order to characterize their propagation modes. In this report we present the frontal gravity wave activity that occurred during a twelve-month period at Millstone Hill (42.6°N, 172.5°W), a mid-latitude site, to illustrate their range of behaviors.     

Remote sensing: A case for moving space data towards the public good

This paper discusses whether current international and national regulation of remote sensing activities achieves a true balance between proprietary interests of producers of remote sensing data and information and the needs of the community in accessing that data and information. By subjecting remote sensing data to general copyright restrictions that are often coupled with exclusive licences, irrespective of type or use of data and/or information, the development of important secondary information markets could be negatively hampered. In the long run, over-regulating access to space data may prove counter-productive in the information age. Using examples of different modes of information dissemination currently being practised, the paper highlights the balances to be drawn between legal issues of private ownership of data and information and public good interests. It concludes with suggestions for a more coherent regulatory approach.     

The ACE Magnetic Fields Experiment

The magnetic field experiment on ACE provides continuous measurements of the local magnetic field in the interplanetary medium. These measurements are essential in the interpretation of simultaneous ACE observations of energetic and thermal particles distributions. The experiment consists of a pair of twin, boom- mounted, triaxial fluxgate sensors which are located 165 inches (=4.19 m) from the center of the spacecraft on opposing solar panels. The electronics and digital processing unit (DPU) is mounted on the top deck of the spacecraft. The two triaxial sensors provide a balanced, fully redundant vector instrument and permit some enhanced assessment of the spacecraft's magnetic field. The instrument provides data for Browse and high-level products with between 3 and 6 vector s−1 resolution for continuous coverage of the interplanetary magnetic field. Two high-resolution snapshot buffers each hold 297 s of 24 vector s−1 data while on- board Fast Fourier Transforms extend the continuous data to 12 Hz resolution. Real-time observations with 1-s resolution are provided continuously to the Space Environmental Center (SEC) of the National Oceanographic and Atmospheric Association (NOAA) for near- instantaneous, world-wide dissemination in service to space weather studies. As has been our team's tradition, high instrument reliability is obtained by the use of fully redundant systems and extremely conservative designs. We plan studies of the interplanetary medium in support of the fundamental goals of the ACE mission and cooperative studies with other ACE investigators using the combined ACE dataset as well as other ISTP spacecraft involved in the general program of Sun-Earth Connections. This revised version was published online in June 2006 with corrections to the Cover Date.     

The Juno Magnetic Field Investigation

The Juno Magnetic Field investigation (MAG) characterizes Jupiter’s planetary magnetic field and magnetosphere, providing the first globally distributed and proximate measurements of the magnetic field of Jupiter. The magnetic field instrumentation consists of two independent magnetometer sensor suites, each consisting of a tri-axial Fluxgate Magnetometer (FGM) sensor and a pair of co-located imaging sensors mounted on an ultra-stable optical bench. The imaging system sensors are part of a subsystem that provides accurate attitude information (to ～20 arcsec on a spinning spacecraft) near the point of measurement of the magnetic field. The two sensor suites are accommodated at 10 and 12 m from the body of the spacecraft on a 4 m long magnetometer boom affixed to the outer end of one of ’s three solar array assemblies. The magnetometer sensors are controlled by independent and functionally identical electronics boards within the magnetometer electronics package mounted inside Juno’s massive radiation shielded vault. The imaging sensors are controlled by a fully hardware redundant electronics package also mounted within the radiation vault. Each magnetometer sensor measures the vector magnetic field with 100 ppm absolute vector accuracy over a wide dynamic range (to 16 Gauss = \(1.6 \times 10^{6}\mbox{ nT}\) per axis) with a resolution of ～0.05 nT in the most sensitive dynamic range (±1600 nT per axis). Both magnetometers sample the magnetic field simultaneously at an intrinsic sample rate of 64 vector samples per second. The magnetic field instrumentation may be reconfigured in flight to meet unanticipated needs and is fully hardware redundant. The attitude determination system compares images with an on-board star catalog to provide attitude solutions (quaternions) at a rate of up to 4 solutions per second, and may be configured to acquire images of selected targets for science and engineering analysis. The system tracks and catalogs objects that pass through the imager field of view and also provides a continuous record of radiation exposure. A spacecraft magnetic control program was implemented to provide a magnetically clean environment for the magnetic sensors, and residual spacecraft fields and/or sensor offsets are monitored in flight taking advantage of Juno’s spin (nominally 2 rpm) to separate environmental fields from those that rotate with the spacecraft.     

Multipath Limitations on Low-Angle Radar Tracking

This paper investigates the problem of tracking targets at a low elevation angle in the presence of specular and diffuse multipath. Quantitative estimates are derived of the elevation angles, and hence, range, at which targets of specified height can be accurately tracked. A parametric approach is followed in which the long-standing uncertainty of how terrain forward-scatters at low grazing angles is recognized at the outset. Particular attention is given to the effects of target motion which permit rejection of multipath components falling outside the radar tracker's passband. The results are presented in a form which can be readily applied to a spectrum of radar trackers with differing requirements. The limited experimental ental data on the specular and diffuse scattering parameters for several generic types of terrain are applied to estimate the significance of multipath under different situations and to indicate specific areas in which additional experimental data are critically needed.