A review of terrestrial radar interferometry for measuring surface change in the geosciences

This paper presents a review of the current state of the art in the use of terrestrial radar interferometry for the detection of surface changes related to mass movement. Different hardware‐types and acquisition concepts are described, which use either real or synthetic aperture for radar image formation. We present approaches for data processing procedures, paying special attention to the separation of high resolution displacement information from atmospheric phase variations. Recent case studies are used to illustrate applications in terrestrial radar interferometry for change detection. Applications range from detection and quantification of very slow moving (millimeters to centimeters per year) displacements in rock walls from repeat monitoring, to rapid processes resulting in fast displacements (~50 m/yr) acquired during single measurement campaigns with durations of only a few hours. Fast and episodic acting processes such as rockfall and snow avalanches can be assessed qualitatively in the spatial domain by mapping decorrelation caused by those processes. A concluding guide to best practice outlines the necessary preconditions that have to be fulfilled for successful application of the technique, as well as in areas characterized by rapid decorrelation. Empirical data from a Ku‐band sensor show the range of temporal decorrelation of different surfaces after more than two years for rock‐surfaces and after a few seconds to minutes in vegetated areas during windy conditions. The examples show that the displacement field can be measured for landslides in dense grassland, ice surfaces on flowing glaciers and snowpack creep. Copyright © 2014 John Wiley & Sons, Ltd.     

Modification of climate signals by human activities recorded in varved sediments (AD 1608–1942) of Lake Holzmaar (Germany)

Paleolimnological data from varved sediments in Lake Holzmaar (Eifel, Germany) were combined with documentary data on human activities, long-term data from the Historical Climate Database (HISKLID) for Germany and with recent monitoring data to evaluate changes in deposition that arose from climatic and human influences. The sediment data included seasonal layer thickness in an established varve chronology (1608–1942 AD), subannual chemical element counts, and multiannual organic matter data (TOC, TN, δ¹³C_org), all combined on an annual scale. Indicators for detritus deposition (lithogenic element counts and detritus layers) determined the first principal component (PC1) of the sediment data. This detritus PC1 was compared to the first PCs of the seasonal precipitation and temperature from HISKLID. While no relation was found to precipitation, the correlation with the temperature PC1 determined by spring to fall temperatures was significant. From 1608 to 1870, a positive correlation of the PCs suggests an increase of detritus deposition in the lake center with increasing non-winter temperatures. These may be linked by lake-internal sediment redeposition that increases when the periods of winter stratification become shorter and that of lake circulation longer. The detritus deposition is modulated by external detritus input depending on the intensity of erosion-conducive land use (wood pasture, wood cutting, and rotational slash-and-burn cultivation). Detritus input diminished when land use slowed down with population decrease as the consequence of plague epidemics, warfare and emigration. After 1870, forest regeneration and improving agricultural practices led to a stabilization of the catchment. Erosion and detritus deposition decreased progressively. The negative correlation of detritus deposition with the gradually increasing temperature presumably mimics a cause-effect relation, although a link with decreasing freeze–thaw action is possible. The modernization of agriculture proceeded with manuring and fertilizing, which caused an increase of lake productivity as indicated by summer blooms of diatoms with enhanced nutrient demand, increased δ¹³C_org values and sulfur concentrations. Within this well established data base we found combinations of criteria that may be used to deduce natural climatic or anthropogenic influences. The quantitative attribution of these influences remains a challenging task in paleolimnology because their interaction makes the detection of linking mechanisms difficult even at high degree of detail and the processes themselves remain debatable.     

From Tethys to Eastern Paratethys: Oligocene depositional environments, paleoecology and paleobiogeography of the Thrace Basin (NW Turkey)

The Oligocene depositional history of the Thrace Basin documents a unique paleogeographic position at a junction between the Western Tethys and the Eastern Paratethys. As part of the Tethys, shallow marine carbonate platforms prevailed during the Eocene. Subsequently, a three-staged process of isolation started with the Oligocene. During the Early Rupelian, the Thrace Basin was still part of the Western Tethys, indicated by typical Western Tethyan marine assemblages. The isolation from the Tethys during the Early Oligocene is reflected by oolite formation and endemic Eastern Paratethyan faunas of the Solenovian stage. The third phase reflects an increasing continentalisation of the Thrace Basin with widespread coastal swamps during the Late Solenovian. The mollusc assemblages are predominated by mangrove dwelling taxa and the mangrove plant Avicennia is recorded in the pollen spectra. The final continentalisation is indicated by the replacement of the coastal swamps by pure freshwater swamps and fluvial plains during the Late Oligocene (mammal zone MP 26). This paleogeographic affiliation of the Thrace Basin with the Eastern Paratethys after ~32 Ma contrasts all currently used reconstructions which treat the basin as embayment of the Eastern Mediterranean basin.     

Ecogeomorphic state variables and phase‐space construction for quantifying the evolution of vegetated aeolian landscapes

Cellular automaton modelling for the simulation of dune field formation and evolution has developed progressively in aeolian geomorphology in the last decade or so. A model that incorporates the effects of vegetation and its interactions with geomorphic landscape development – the Discrete Ecogeomorphic Aeolian Landscapes (DECAL) model – can replicate a number of important visual and qualitative aspects of the complex evolution of aeolian dune landscapes under the influence of vegetation dynamics in coastal environments. A key challenge in this research area is the analysis and comparison of both simulated and real‐world vegetated dune landscapes using objective and quantifiable principles. This study presents a methodological framework or protocol for numerically quantifying various ecogeomorphic attributes, using a suite of mathematically defined landscape metrics, to provide a rigorous and statistical evaluation of vegetated dune field evolution. Within this framework the model parameter space can be systematically explored and simulation outcomes can be methodically compared against real‐world landscapes. Based on a simplified scenario of parabolic dunes developing out of blow‐outs the resulting dune field realizations are investigated as a function of variable growth vigour of two simulated vegetation types (pioneer grass and successional woody shrub) by establishing a typological phase‐diagram of different landscape classes. The set of simulation outcomes furthermore defines a higher‐dimensional phase‐space, whose axes or dimensions can be interpreted by analysing how individual ecogeomorphic landscape metrics, or state variables, contribute to the data distribution. Principal component analysis can reduce this to a visual three‐dimensional (3D) phase‐space where landscape evolution can be plotted as time‐trajectories and where we can investigate the effects of changing environmental conditions partway through a simulation scenario. The use of landscape state variables and the construction of a 3D phase‐space presented here may provide a general template for quantifying many other eco‐geomorphic systems on the Earth's surface. Copyright © 2010 John Wiley & Sons, Ltd.     

Use of C-Band frequencies for satellite navigation: benefits and drawbacks

Although not considered for the first generation of European Galileo satellites, the use of C-Band frequencies for navigation purposes may be taken into account for a future generation of Galileo. For this reason, a frequency band of 20 MHz bandwidth (5,010–5,030 MHz) has been allocated in the course of the World Radio Communications Conference 2000 held in Istanbul, Turkey. The use of C-Band navigation signals offers both advantages and drawbacks. One example is the ionospheric path delay which is inversely proportional to the (squared) carrier frequency and is therefore significantly smaller at C-Band. On the other hand, the use of C-Band frequencies results in increased attenuation effects such as free space loss or rainfall attenuation. It is therefore necessary to provide a detailed analysis of the effects of C-Band frequencies on the navigation process. In order to assess the feasibility of using C-Band frequencies, various aspects of signal propagation and satellite signal tracking at C-Band are examined in the context of this article. In particular, aspects like free space loss, atmospheric effects, foliage attenuation, code and carrier tracking performance, code noise, phase noise and multipath are discussed with respect to their performance at C-Band. In order to allow comparison with the current GPS system, the performance at C-Band is compared to the L-Band performance under similar or identical conditions. The results of this analysis will finally be discussed with respect to their impact on satellite payload and receiver design.

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An experimental analysis of three methods for highlighting colorful pictographic symbols

Highlighting is one of the key functionalities of any interactive visualization environment. Yet, there is little research on highlighting methods. This article focuses on highlighting of colorful pictographic symbols. Three strategies for highlighting were tested by implementing three highlighting methods that were suggested suitable in the literature on attention, perceptual grouping, and motion detection. An experimental design measuring response times and accuracy was used and subjective opinions were collected. The three available strategies for applying the highlighting effect to a subset of visually salient (i.e., colorful) symbols are: (1) to decrease the saliency of the non-highlighted symbols, (2) to increase the saliency of the highlighted symbols, and (3) to add a connecting element for grouping the highlighted symbols. Of these strategies, adding a connecting element was found to be the least efficient based on the response times, whereas both methods for tuning the saliency difference between the highlighted and non-highlighted symbols were found to be equally efficient. However, decreasing the saliency of the non-highlighted symbols was clearly preferred in the subjective evaluation.     

Extracting commuter-specific destination hotspots from trip destination data – comparing the boro taxi service with Citi Bike in NYC

ABSTRACT

Taxi trajectories from urban environments allow inferring various information about the transport service qualities and commuter dynamics. It is possible to associate starting and end points of taxi trips with requirements of individual groups of people and even social inequalities. Previous research shows that due to service restrictions, boro taxis have typical customer destination locations on selected Saturdays: many drop-off clusters appear near the restricted zone, where it is not allowed to pick up customers and only few drop-off clusters appear at complicated crossing. Detected crossings imply recent infrastructural modifications. We want to follow up on these results and add one additional group of commuters: Citi Bike users. For selected Saturdays in June 2015, we want to compare the destinations of boro taxi and Citi Bike users. This is challenging due to manifold differences between active mobility and motorized road users, and, due to the fact that station-based bike sharing services are restricted to stations. Start and end points of trips, as well as the volumes in between rely on specific numbers of bike sharing stations. Therefore, we introduce a novel spatiotemporal assigning procedure for areas of influence around static bike sharing stations for extending available computational methods.