Determination of high-precision GPS orbits using triple differencing technique

Summary Precise orbits of the Global Positioning System (GPS) satellites are fundamental constituents of GPS-based space geodesy. Accurate baseline estimates with a precision of one to a few parts in 10⁸ are essential to the study of Earth's dynamics problems. As a by-product of trajectory estimation, high resolution Earth Rotation Parameters (ERPs) can also be determined. A new application of triple differencing for efficient evaluation of GPS orbits in a PC environment is presented here. Initial tests show that this approach is capable of providing orbits that are highly compatible with the results obtained by the International GPS Service for Geodynamics (IGS). This approach allows for completely automated data processing without the overhead of working with very large normal matrices or cycle-slip fixing.     

The porosity and permeability of chondritic meteorites and interplanetary dust particles

Abstract— We have investigated the porosity of a large number of chondritic interplanetary dust particles (IDPs) and meteorites by three techniques: standard liquid/gas flow techniques, a new, noninvasive ultrasonic technique, and image processing of backscattered images. The latter technique is obviously best-suited to sub-kilogram sized samples. We have also measured the gas and liquid permeabilities of some chondrites by two techniques: standard liquid/gas flow techniques, and a new, nondestructive pressure release technique. We find that chondritic IDPs have a somewhat bimodal porosity distribution. Peaks are present at 0 and 4% porosity; a tail then extends to 53%. Type 1–3 chondrite matrix porosities range up to 30%, with a peak at 2%. The bulk porosities for type 1–3 chondrites have the same approximate range as exhibited by the matrix, which indicates that other components of the bulk meteorites (including chondrules and aggregates) have the same average porosity as the matrix. These results reveal that the porosities of primitive materials at scales ranging from nanogram to kilogram are similar, which implies that similar accretion dynamics operated through 12 orders of size magnitude. Permeabilities of the investigated chondrites vary by several orders of magnitude, and there appears to be no simple dependence of permeability with degree of aqueous alteration, chondrite type or porosity.     

THE SUN BELT-SNOW BELT: A CASE OF SLOPPY REGIONALIZING

The Sun Belt has become a part of the American vocabulary without a careful examination of its validity as a region. This analysis, using a variety of techniques and variables taken from the topics of federal involvement, economic well-being, and population change, concludes that the Sun Belt does not emerge as a distinct and homogeneous region. The Snow Belt would be better expressed as the Core (the old Manufacturing Belt).