UCL University College London Eprints
UCL Eprints collects the work of UCL researchers and makes it freely available over the web, helping the worldwide scholarly community to discover UCL research. Institutional repositories like UCL Eprints complement the traditional academic publishing and scholarly communications processes. They raise the visibility of research and help to maximise its impact. UCL researchers are encouraged to deposit a copy of each journal article, conference paper, working paper, and any other research output, in the UCL Eprints at the earliest opportunity, ensuring that their research reaches as wide an audience as possible.
Mostrando recursos 61 - 80 de 317,334
PITCH ANGLE DIFFUSION OF LOW-ENERGY ELECTRONS BY WHISTLER MODE WAVES - JOHNSTONE, AD; WALTON, DM; LIU, R; HARDY, DA
It has often been argued that electrons with energy below approximately 10 keV cannot be pitch-angle diffused by whistler mode waves because they have less than a critical minimum parallel energy. We show that there is no theoretical justification for an energy threshold based on the grounds of either resonance or instability and present energy/pitch angle plots from the low energy plasma analyzer (LEPA) on the CRRES spacecraft which support this analysis because they have features to be expected from a whistler mode interaction. This shows that whistler mode diffusion is responsible for a substantial amount of low-energy electron precipitation...
Satellite sensor intercalibration over Dome C: An introduction to QA4EO and the ESA GlobAlbedo project - Potts, D; Mackin, S; Muller, JP; Fox, N
In this paper, the response of 7 Earth observation satellite sensors from multiple platforms, as well as different sensors on the same platform, are cross-compared over the Dome C plateau, Antarctica, during the austral summer of 2008-2009. A single, unified methodology is employed to remove geometric, temporal and atmospheric biases between different sensors with a range of spatial resolutions, bandwidths and overpass times. The result assumes no “correct” baseline value, only relative responses. The method is derived from an in-depth sensitivity analysis, presented elsewhere , , that takes into account: BRDF effect, cloud cover, macro-scale hoar-frost change and variations in...
The creation, assessment and 3D visualisation of multi-resolution DTMs for the assessment of Mars potential landing sites for surface exploration. - Kim, JR; Lin, SY; Muller, JP; Warner, N; Gupta, S
One of the key issues for planetary, especially Mars surface exploration, is how landing sites for future rovers, sample return missions and landers can be objectively selected considering topographic variables such as slope, altitude and roughness as well as their physical scattering properties and how a detailed pre-assessment of selected landing sites can be performed. For these purposes, stereo analysis has been proposed as the best possible solution to provide reliable topographic data. Recently, a number of successful missions to Mars have taken place involving the ESA (European Space Agency) Mars Express mission including the HRSC (High Resolution Stereo Camera)...
Stereo retrievals of cloud and smoke winds and heights from EO platforms: past, present and future - Muller, JP; Fisher, D; Yershov, V
The justification for the use of stereo motion vectors (SMVs) derived from instruments such as the NASA MISR (Multiangle Imaging Spectro-Radiometer), ESA AATSR (Advanced Along Track Scanning Radiometer) and future Sentinel-3 SLSTR is given. Examples are shown of cloud-top heights and winds (Stereo Motion Vectors, SMVs) using the M2/3 stereo matching system described by (Muller et al., 2002) and its modification, M4, for AATSR (Muller et al., 2007). Examples are also shown of the application of a modified scheme, M6 for smoke-plume injection height (Fisher et al., 2012) and its validation using CALIPSO. A new algorithm for better discrimination of...
Exploiting ten years of MERIS data over land surfaces - Gobron, N; Dash, J; Arino, O; Gascon, LH; Muller, JP
Envisat's Medium Resolution Imaging Spectrometer (MERIS) acquired multi-spectral imagery of the Earth in the optical domain over terrestrial surfaces for a decade at global scale. For the last ten years, scientists have used multi-spectral data or terrestrial geophysical products for characterizing the state of the global system and its variability. Our paper shows highlights of several achievements of the use of MERIS data over terrestrial surfaces but specifically focuses on regional to global scale applications. We first summarize daily operational biophysical parameters and present examples of their uses for the monitoring of land surface states and changes, especially related to...
Global warping coefficients for improving ATSR co-registration - Fisher, D; Muller, J
Globally applicable warping coefficients for improving the co-registration between the forward and nadir views of the series of Along-Track Scanning Radiometer (ATSR) instruments are presented. The coefficients are derived from a polynomial- based warp, using a least squares fit on a set of automatically detected forward to nadir tie points. In-depth statistical analysis is presented here covering both an independent analysis of the warping coefficients using the Pyramidal-Gotcha algo- rithm and a global assessment using the Speeded Up Robust Features tie-pointing algorithm. This independent assessment shows that the co-registration between the nadir and forward views improves in all cases to...
Degradation of Cyanobacterial Biosignatures by Ionizing Radiation - Dartnell, LR; Storrie-Lombardi, MC; Mullineaux, CW; Ruban, AV; Wright, G; Griffiths, AD; Muller, J; Ward, JM
Primitive photosynthetic microorganisms, either dormant or dead, may remain today on the martian surface, akin to terrestrial cyanobacteria surviving endolithically in martian analog sites on Earth such as the Antarctic Dry Valleys and the Atacama Desert. Potential markers of martian photoautotrophs include the red edge of chlorophyll reflectance spectra or fluorescence emission from systems of light-harvesting pigments. Such bio- signatures, however, would be modified and degraded by long-term exposure to ionizing radiation from the unshielded cosmic ray flux onto the martian surface. In this initial study into this issue, three analytical techniques—absorbance, reflectance, and fluorescence spectroscopy—were employed to determine the...
Photostability and fluorescence-based detection of PAHs on the Martian surface - Dartnell, LR; Patel, MR; Storrie-Lombardi, MC; Ward, JM; Muller, JP
Even in the absence of any biosphere on Mars, organic molecules, including polycyclic aromatic hydrocarbons (PAHs), are expected on its surface due to delivery by comets and meteorites of extraterrestrial organics synthesized by astrochemistry, or perhaps in situ synthesis in ancient prebiotic chemistry. Any organic compounds exposed to the unfiltered solar ultraviolet spectrum or oxidizing surface conditions would have been readily destroyed, but discoverable caches of martian organics may remain shielded in the subsurface or within surface rocks. We have studied the stability of three representative polycyclic aromatic hydrocarbons (PAHs) in a Mars chamber, emulating the ultraviolet spectrum of unfiltered...