A method for discovery and analysis of temporal patterns in complex event data     

Donna J. Peuquet  Anthony C. Robinson  Samuel Stehle  Franklin A. Hardisty  Wei Luo 《International journal of geographical information science》2013,27(9):1588-1611

Pattern analysis techniques currently common within geography tend to focus either on characterizing patterns of spatial and/or temporal recurrence of a single event type (e.g., incidence of flu cases) or on comparing sequences of a limited number of event types where relationships between events are already represented in the data (e.g., movement patterns). The availability of large amounts of multivariate spatiotemporal data, however, requires new methods for pattern analysis. Here, we present a technique for finding associations among many different event types where the associations among these varying event types are not explicitly represented in the data or known in advance. This pattern discovery method, known as T-pattern analysis, was first developed within the field of psychology for the purpose of finding patterns in personal interactions. We have adapted and extended the T-pattern method to take the unique characteristics of geographic data into account and implemented it within a geovisualization toolkit for an integrated computational-geovisual environment we call STempo. To demonstrate how T-pattern analysis can be employed in geographic research for discovering patterns in complex spatiotemporal data, we describe a case study featuring events from news reports about Yemen during the Arab Spring of 2011–2012. Using supplementary data from the Global Database of Events, Language, and Tone, we briefly summarize and reference a separate validation study, then evaluate the scalability of the T-pattern approach. We conclude with ideas for further extensions of the T-pattern technique to increase its utility for spatiotemporal analysis.  相似文献   

LANDSAT Sub-pixel Analysis in Mapping Impact of Climatic Variability on Prairie Pothole Changes     

Bo Zhang  Franklin W Schwartz  Daoqin Tong 《Transactions in GIS》2009,13(2):179-195

The Prairie Pothole Region in the United States contains millions of seasonal, semi-permanent, or permanent lakes and wetlands that typically range in size from 0.1 to 10 ha. These lakes and wetlands are vulnerable to climate change, especially in our study area in South Dakota, in which a period of deluge following a sharp drought considerably expanded the areal extent of prairie pothole lakes during the last decade of the twentieth century. Preliminary estimates of lake areas, determined using LANDSAT 5 and 7 images, had appreciable errors especially for the smallest of these lakes. This article describes a new sub-pixel approach integrated with a CART (Classification and Regression Tree) model using a GIS (Geographical Information System) to quantify mixed water pixels along lake boundaries to improve area estimations for pothole lakes. Errors in estimated area were typically 10% or less for lakes greater than 1 ha in size. An analysis of lakes in our study area demonstrates how lake area changed with the transition from drought to deluge. Small lakes exhibited a distinct seasonal variation in contrast to large lakes that tended to follow precipitation trends more broadly. The total water area of lakes is consistent with broad variation in rainfall.  相似文献   

Gas flux and carbonate occurrence at a shallow seep of thermogenic natural gas   总被引：1，自引：1，他引：0  

Franklin S. Kinnaman  Justine B. Kimball  Luis Busso  Daniel Birgel  Haibing Ding  Kai-Uwe Hinrichs  David L. Valentine 《Geo-Marine Letters》2010,30(3-4):355-365

The Coal Oil Point seep field located offshore Santa Barbara, CA, consists of dozens of named seeps, including a peripheral ～200 m² area known as Brian Seep, located in 10 m water depth. A single comprehensive survey of gas flux at Brian Seep yielded a methane release rate of ～450 moles of CH₄ per day, originating from 68 persistent gas vents and 23 intermittent vents, with gas flux among persistent vents displaying a log normal frequency distribution. A subsequent series of 33 repeat surveys conducted over a period of 6 months tracked eight persistent vents, and revealed substantial temporal variability in gas venting, with flux from each individual vent varying by more than a factor of 4. During wintertime surveys sediment was largely absent from the site, and carbonate concretions were exposed at the seafloor. The presence of the carbonates was unexpected, as the thermogenic seep gas contains 6.7% CO₂, which should act to dissolve carbonates. The average δ¹³C of the carbonates was ?29.2?±?2.8‰ VPDB, compared to a range of ?1.0 to +7.8‰ for CO₂ in the seep gas, indicating that CO₂ from the seep gas is quantitatively not as important as ¹³C-depleted bicarbonate derived from methane oxidation. Methane, with a δ¹³C of approximately ?43‰, is oxidized and the resulting inorganic carbon precipitates as high-magnesium calcite and other carbonate minerals. This finding is supported by ¹³C-depleted biomarkers typically associated with anaerobic methanotrophic archaea and their bacterial syntrophic partners in the carbonates (lipid biomarker δ¹³C ranged from ?84 to ?25‰). The inconsistency in δ¹³C between the carbonates and the seeping CO₂ was resolved by discovering pockets of gas trapped near the base of the sediment column with δ¹³C-CO₂ values ranging from ?26.9 to ?11.6‰. A mechanism of carbonate formation is proposed in which carbonates form near the sediment–bedrock interface during times of sufficient sediment coverage, in which anaerobic oxidation of methane is favored. Precipitation occurs at a sufficient distance from active venting for the molecular and isotopic composition of seep gas to be masked by the generation of carbonate alkalinity from anaerobic methane oxidation.