Examining the C1-P1 Pseudorange Bias

Use of GPS tracking data from different dual-frequency receiver types (cross-correlating vs. codeless) has revealed satellite-dependent biases in pseudorange observables P1 (Y-code) and C1 (C/A, Clear Acquisition code). These biases can have a direct effect on clock estimates, carrier phase bias fixing, and other parameters estimated in GPS data processing. A set of satellite-specific compensatory pseudorange offsets is calculated, and each is applied to a wee of daily global network analyses in which satlellite, receiver, atmospheric, and Earth rotation parameters are estimated. Results from these analyses are then compared to those from corresponding baseline cases in which no biases were applied. There is also some evidence that suggests that the pseudorange biases differ even among codeless receiver models. Hence, a second set of offsets is computed on a different basis, and compared with the baseline model in a similar manner. A preliminary examination of C1-P1 variations over time is presented. Finally, recommendations are made for the use of the calculated offsets, and consideration is given to a future dissemination of updates to these values as necessary. ? 2001 John Wiley & Sons, Inc.     

Efficacy of minnow traps for sampling mummichogs in tidal marshes

We evaluated two types of wire-mesh minnow traps for sampling mummichogs (Fundulus heteroclitus) from intertidal rivulets on the surface of a salt marsh. In field trials, mean catch (no. of fish trap⁻¹) did not differ significantly between trap types nor across soak times ranging from 30 to 240 min. Catch rate (no. of fish trap⁻¹ min⁻¹) was significantly (K-W ANOVA on ranked data, H_4df=24.79; p<0.001) greater at shorter soak times, and larger size classes (>45 mm TL) of fish were relatively more abundant (Kolmogorov-Smirnov test, p<0.0001) in collections from double-funnel cylindrical traps (volume=10,330 cm³) compared to rectangular traps having about twice the volume and a single funnel cylindrical traps (volume=10,330 cm³) compared to rectangular traps having about twice the volume and a single funnel opening. We estimated entry and escape rates by adding marked fish to traps at initial densities of 30, 60, and 120 trap⁻¹ and measuring changes in the numbers of marked and unmarked fish in each trap type at soak times ranging from 15 to 120 min during the flood stage of the tidal cycle. Escape rate was almost, twice as great from the two-funnel cylindrical traps (0.77 fish min⁻¹) than from the single-funnel rectangular type (0.42 fish min⁻¹) but entry rates did not differ significantly (K-W ANOVA, H_4df=0.06; p=0.813) between trap types. Escape rate increased and entry rate decreased as fish density within traps was increased. Escape rates were highest immediately following immersion of the traps, but approached a constant value after 30 min. Trap-specific rates of entry and escape can be affected by a variety of factors including physical characteristics of different trap types, method and timing of trap deployment, and fish behavior. Catch data from minnow traps are unlikely to be useful in measuring relative abundance of mummichogs among habitats unless very short soak times (≤60 min) are used and calibration tests are performed. Use of longer soak times virtually ignores the dynamics involved in determining catch, and is unlikely to provide accurate information on either abundance or size distribution of mummichogs from tidal marsh habitats.     

Aircraft wind measurement considering lift-induced upwash

Flow distortion is a universal consideration in the measurement of wind. Usually the distortion results from deflection of the flow by the support. Instruments mounted on airplanes, however, experience an additional deflection associated with lift, which changes rapidly and continuously during flight. In front of the airplane, this deflection appears as upwash. Characteristic upwash contamination ranges from 0.5 to 2.5 m s^-1, depending on wing loading, flight speed, and forward distance from the wing to the measurement location. On pressure-radome installations the distance from the wing is usually small and the potential for upwash contamination large. Sensors mounted at the end of long probes attached to smaller airplanes with light wing loading are less susceptible to upwash contamination. Since wing loading also depends on the local vertical wind velocity the upwash velocity is directly correlated with vertical wind velocity. Generally, empirical corrections are derived from flight tests. We develop a simple method from principles of aerodynamics which explains these corrections in terms of upwash. The applicability of our approach to moderate upwash is demonstrated with data collected from the NOAA Long-EZ research airplane. More severe upwash conditions require a more sophisticated correction beyond the scope of this paper, but basically derived from the same principles.Oak Ridge Associated Universities, assigned to NOAA/ATDD     

High chromium contents in Tertiary coal deposits of northwestern Washington — A key to their depositional history

Chromium contents obtained from 20 coal and 5 associated rock samples collected from the basal part of the Eocene Chuckanut Formation, in Skagit and Whatcom counties, northwest Washington, range between 30 and 300 ppm (mean 120 ppm whole-coal basis). The lenticular coals, ranging in rank from subbituminous to anthracite, and with an ash content of 12–46%, crop out along the western flank of the Cascade Range. Results of X-ray diffraction analysis of low-temperature ash show that the mineral matter in the coal samples consists predominantly of quartz and clay (kaolinite, illite and chlorite group). However, accessory minerals, isolated from the coal samples and analyzed by X-ray diffraction, scanning electron microscope and optical methods, contain angular fragments and euhedral crystals of the spinel group (chromite, magnetite and trevorite ), kaolinite-serpentine group (antigorite and chrysotile), chlorite group, amphibole group and pyroxene group minerals (augite, diopside and enstatite), all of which are commonly enriched in chromium.Although associated primarily with the inorganic fraction of the coal, concentrations of chromium in the samples show no statistically significant correlation with ash content. Localized concentrations of chromium in the coal are the result of natural contamination from the alteration of detrital chromium-bearing mineral grains introduced into the peat-forming mires from nearby Jurassic ophiolite bodies. The coals formed in the early Eocene, in rapidly subsiding small basins that developed during the uplift and erosion of the pre-Tertiary ophiolite terrain. Scattered bodies of source rock, random distribution of chromium-bearing minerals within the coal and sample heterogeneity account for the variation in Cr contents of the samples.     

Some exact solutions for the flow of fluid through tubes with uniformly porous walls

Summary This paper considers an incompressible fluid flowing through a straight, circular tube whose walls are uniformly porous. The flow is steady and one dimensional. The loss of fluid through the wall is proportional to the mean static pressure in the tube. Several formulations of the wall shear stress are considered; these formulations were motivated by the results from Hamel's radial flow problem, boundary layer flows/and boundary layer suction profiles. For each of these formulations exact solutions for the mean axial velocity and the mean static pressure of the fluid are obtained. Sample results are plotted on graphs. For the constant wall shear stress problem, the theoretical solutions compare favorably with some experimental results.Notations A, B, D, E constant parameters - a, b constant parameters - Ai(z), Bi(z) Airy functions - Ai, Bi derivatives of Airy functions - k constant of proportionality betweenV andp - L length of pores - p,p mean static pressure - p ₀ static pressure outside the tube - p ₀ value ofp atx=0 - Q constant exponent - R inside radius of the tube - T wall shear stress - T ₀ shear parameter - t wall thickness - U free stream velocity - ,u mean axial velocity - u ₀ value ofu atx=0 - V,V mean seepage velocity through the wall - v ₀ mean seepage velocity - x,x axial distance along the tube - z transformed axial distance - z ₀ value ofz atx=0 - mean outflow angle through the wall - cos - density of the fluid - wall shear stress - dynamic viscosity of the fluid - over-bar dimensional terms - no bar nondimensional terms The National Center for Atmospheric Research is sponsored by the National Science Foundation     

Equilibrium temperatures of interstellar iron grains

Because of the relatively low number densities found in typical interstellar clouds, molecules observed there must be produced by a combination of both two-body gas-phase reactions and surface reactions. The latter type includes various catalytic reactions, such as the formation of H₂ on transition metal grains. These reactions are very temperature dependent, the grain temperature appearing in the exponential of the rate equations. Because of the small heat capacities of the grains due to their small sizes, they may be subject to considerable fluctuations in temperature. This problem is examined for iron grains and found to be minimal for sizes greater than 100 Å. Steady-state equilibrium temperatures are then calculated for a size distribution of iron particles ranging from 10³ to 10⁹ atoms per grain by a refined method of an earlier work by one of us (RGT). The results are that iron grain temperatures are significantly greater than those of dielectric grains of comparable size in the same radiation field.