Modeling Checkpoint-Based Movement with the Earth Mover's Distance

Movement data comes in various forms, including trajectory data and checkpoint data. While trajectories give detailed information about the movement of individual entities, checkpoint data in its simplest form does not give identities, just counts at checkpoints. However, checkpoint data is of increasing interest since it is readily available due to privacy reasons and as a by-product of other data collection. In this paper we propose to use the Earth Mover’s Distance as a versatile tool to reconstruct individual movements or flow based on checkpoint counts at different times. We analyze the modeling possibilities and provide experiments that validate model predictions, based on coarse-grained aggregations of data about actual movements of couriers in London, UK. While we cannot expect to reconstruct precise individual movements from highly granular checkpoint data, the evaluation does show that the approach can generate meaningful estimates of object movements. B. Speckmann and K. Verbeek are supported by the Netherlands Organisation for Scientific Research (NWO) under project nos. 639.023.208 and 639.021.541, respectively. This paper arose from work initiated at Dagstuhl seminar 12512 “Representation, analysis and visualization of moving objects”, December 2012. The authors gratefully acknowledge Schloss Dagstuhl for their support

Trophic overlap between three syntopic semi-aquatic carnivores: Cape clawless otter, spotted-necked otter and water mongoose

Drought conditions in the Eastern Cape Province, South Africa, from 1990 to 1993 caused much of the Bushmans River to dry up, thus forcing Cape clawless otters Aonyx capensis (Schinz), spotted-necked otters Lutra maculicollis (Lichtenstein) and water mongooses Atilax paludinosus (Cuvier) to coexist in restricted ranges. The diet of the three carnivores was compared by analysing their scats to determine the amount of trophic overlap. Expressed as relative percentage frequency, the three most common prey categories found in Cape clawless otter scats were crab Potamonautes perlatus (Milne Edwards) (51%), insect (19%) and fish Tilapia sparrmanii (Smith) (18%). In spotted-necked otter scats, fish (47%), crab (38%) and frog (8%) were the most common, while in water mongoose scats, insect (28%), crab (26%) and mammal (15%) were most abundant. Water mongooses and spotted-necked otters ate similar sizes of crabs, significantly larger than those eaten by the Cape clawless otters. Cape clawless otters ate a wide range of crab sizes, including specimens much larger than those taken by the other two carnivores. Cape clawless otters and water mongooses ate similar size fish, significantly smaller than spotted-necked otters. The results show that even during enforced cohabitation in a relatively small range during drought conditions, there is separation of diets in these three carnivores.Articl

The Last Glacial Maximum and deglaciation in southern South America.

This paper models the extent of the Patagonian icesheet during the Last Glacial Maximum (LGM) and its subsequent deglaciation. It constrains a new coupled icesheet/climate numerical model with empirical evidence and simulates the icesheet at the LGM and at stages of deglaciation. Under LGM conditions an icesheet with a modelled volume slightly in excess of 500,000km3 builds up along the Andes. There is a marked contrast between the maritime and continental flanks of the modelled icesheet, with positive mass balance exceeding 2m in the west and declining tenfold to the east. Modelled ice velocities commonly reach 400myr-1 in the western fjords. The model is most sensitive to variations in temperature and good agreement between modelled ice extent and empirical evidence was achieved by applying a temperature decrease of 6oC relative to present day temperatures with constant wind fields over the model domain. Assuming a stepped start to deglaciation, modelled ice volumes declined sharply, contributing 1.2m to global sea level, 80% of it within 2000 years. The empirical record suggests that such a stepped warming occurredaround17,500– 17,150 cal yr ago

Late-Glacial Glacier Events in Southernmost South America: A Blend of 'Northern' and 'Southern' Hemispheric Climatic Signals?

This paper examines new geomorphological, chronological and modelling data on glacier fluctuations in southernmost South America in latitudes 46–55°S during the last glacial–interglacial transition. Establishing leads and lags between the northern and southern hemispheres and between southern mid-latitudes and Antarctica is key to an appreciation of the mechanisms and resilience of global climate. This is particularly important in the southern hemisphere where there is a paucity of empirical data. The overall structure of the last glacial cycle in Patagonia has a northern hemisphere signal. Glaciers reached or approached their Last Glacial Maxima on two or more occasions at 25–23 ka (calendar) and there was a third less extensive advance at 17.5 ka. Deglaciation occurred in two steps at 17.5 ka and at 11.4 ka. This structure is the same as that recognized in the northern hemisphere and taking place in spite of glacier advances occurring at a time of high southern hemisphere summer insolation and deglaciation at a time of decreasing summer insolation. The implication is that at orbital time scales the ‘northern’ signal dominates any southern hemisphere signal. During deglaciation, at a millennial scale, the glacier fluctuations mirror an antiphase ‘southern’ climatic signal as revealed in Antarctic ice cores. There is a glacier advance coincident with the Antarctic Cold Reversal at 15.3– 12.2 ka. Furthermore, deglaciation begins in the middle of the Younger Dryas. The implication is that, during the last glacial–interglacial transition, southernmost South America was under the influence of sea surface temperatures, sea ice and southern westerlies responding to conditions in the ‘southern’ Antarctic domain. Such asynchrony may reflect a situation whereby, during deglaciation, the world is more sensitized to fluctuations in the oceanic thermohaline circulation, perhaps related to the bipolar seesaw, than at orbital timescales