On uncertainties in carbon flux modelling and remotely sensed data assimilation: The Brasschaat pixel case

Uncertainty on carbon fluxes is determined by the uncertainties of ecosystem model structure, data and model parameter uncertainties and the temporal and spatial inaccuracy of the input data retrieval. The objective of this paper is to understand the error propagation and uncertainty of evaporative fraction (EF), soil moisture content (SMC) and water limited net ecosystem productivity (NEP). In this respect, C-Fix and spaceborne remote sensing are used for the ‘Brasschaat’ pixel. A simple model based on error theory and a Monte-Carlo approach are used. Different error scenarios are implemented to assess input uncertainty on EF, SMC and NEP as estimated with C-Fix.     

C. M. Carollo,H. C. Ferguson and R. F. G. Wyse (eds.), The Formation of Galactic Bulges

Space Science Reviews -     

Ground-multi path mitigation via polarization steering of GPS signal

Multipath (MP) is the dominant error source in Global Positioning System (GPS) code-based position solutions requiring high accuracy. A technique is introduced here to mitigate error due to ground-reflected MP signals. The technique uses two orthogonal dipoles to capture the direct GPS signal and the ground-reflected GPS signal. Adjusting the amplitude and phase of the received voltage between the two dipoles can reduce the impact of MP error. Theoretical derivations of this technique are performed for a GPS signal upon reflection from dry soil, seawater, and fresh water. The theoretical results are verified with a real world experiment on the aforementioned surfaces. GPS pseudo-range (PR) and carrier-to-noise ratio (C/No) measurements for specific satellites are used to verify the predicted theoretical results.     

Experimental results for Titan aerobot thermo-mechanical subsystem development

This paper describes experimental results from a development program focused on maturing Titan aerobot technology in the areas of mechanical and thermal subsystems. Results from four key activities are described: first, a cryogenic balloon materials development program involving coupon and cylinder tests and culminating in the fabrication and testing of an inflated 4.6 m long prototype blimp at 93 K; second, a combined lab experiment and numerical simulation effort to assess potential problems resulting from radioisotope power source waste heat generation near an inflated blimp; third, an aerial deployment and inflation development program consisting of laboratory and helicopter drop tests on a near full scale (11 m long) prototype blimp; and fourth, a proof of concept experiment demonstrating the viability of using a mechanically steerable high gain antenna on a floating blimp to perform direct to Earth telecommunications from Titan. The paper provides details on all of these successful activities and discusses their impact on the overall effort to produce mature systems technology for future Titan aerobot missions.     

Planetary Magnetic Dynamo Effect on Atmospheric Protection of Early Earth and Mars

In light of assessing the habitability of Mars, we examine the impact of the magnetic field on the atmosphere. When there is a magnetic field, the atmosphere is protected from erosion by solar wind. The magnetic field ensures the maintenance of a dense atmosphere, necessary for liquid water to exist on the surface of Mars. We also examine the impact of the rotation of Mars on the magnetic field. When the magnetic field of Mars ceased to exist (about 4 Gyr ago), atmospheric escape induced by solar wind began. We consider scenarios which could ultimately lead to a decrease of atmospheric pressure to the presently observed value of 7 mbar: a much weaker early martian magnetic field, a late onset of the dynamo, and high erosion rates of a denser early atmosphere.     

Recent work correlating the 11-year solar cycle with atmospheric elements grouped according to the phase of the Quasi-Biennial Oscillation

Atmospheric elements at all levels from the surface to the Middle Atmosphere show a probable association with the 11-year solar cycle in northern winter, which can be observed only if the data are grouped according to the phase of the Quasi-Biennial Oscillation. As the correlations are often of opposite sign in the East and West phase of the QBO, the correlation coefficients are mostly small when one uses as full time series of an atmospheric element. The spatial patterns of the correlations resemble well-known teleconnection patterns. The sparse data and short series on the Southern Hemisphere permit only a limited investigation. Good relationships are found in the antarctic stratosphere in spring and at sea level in winter.Statistical tests suggest that our results did not occur by chance, but since we cannot examine data from before 1952 because we do not know the phase of the QBO before then, and since there is no physical explanation for the large correlation coefficients, we cannot yet exclude the possibility that the results are due to sample variation.Affiliate Scientist at NCAR.Visiting Scientist, Freie Universität Berlin.The National Center for Atmospheric Research is sponsored by the National Science Foundation.     

Flare precursors and onset

We report on the progress of a search for precursors that have direct physical connections to the start of subsequent solar flares. The discussion includes recent results at radio, visible, ultraviolet, and x-ray wavelengths, which are relevant to the pre-impulsive (onset) phase. We also relate the aspects of a theoretical scenario, based on magnetic reconnection with transport-coefficient phase changes, for explaining flare onset. The pertinent time scales for pre-impulsive temporal developments are discussed.     

Perturbation solution of attitude motion under body-fixed torques

Approximate analytical solutions are established for the attitude rates and angles of a rigid body subjected to a constant body-fixed torque. The perturbation solutions obtained are valid for any arbitrary inertia parameters. The small parameter is defined as the ratio between representative transverse rotation rate and the spin or scan rate. The results should be useful for quickly evaluating the attitude response of a spin-stabilised or scanning spacecraft to a variety of torque inputs. The applicability of the theory is illustrated by means of practical examples such as the spin-down due to rate coupling of ESA's GEOS spacecraft and the prediction of the attitude drift of the HIPPARCOS satellite during payload initialisation. Furthermore, the compact first-order results should be suitable for implementation in on-board manoeuvre or attitude control software.