Using platforms of opportunity to determine the occurrence and group characteristics of orca (Orcinus orca) in the Hauraki Gulf,New Zealand     

K Hupman  IN Visser  E Martinez  KA Stockin 《新西兰海洋与淡水研究杂志》2013,47(1):132-149

We present the first fine-scale data relating to the occurrence and group characteristics for killer whales (Orcinus orca) in the Hauraki Gulf, New Zealand, as observed from a platform of opportunity (PoP). Group size and composition were examined in relation to water depth and sea surface temperature (SST). From 2000 to 2010, 119 orca encounters were recorded, involving 1 to 18 animals. The encounter rate varied seasonally, being highest in austral spring and lowest in summer. Water depth in which whales were observed was significantly affected by group composition. Sixty-seven percent of groups contained immature animals. Group size was highly skewed towards smaller groups comprising two animals. While this study illustrates that PoPs can be used to indicate the occurrence and group characteristics of highly mobile social species, biases clearly exist. Through identifying such inaccuracies, we present recommendations on how future data should be collected to minimise error and improve datasets for scientific use.  相似文献   

Assessment of observing time-variable gravity from GOCE GPS and accelerometer observations   总被引：2，自引：1，他引：1  

P. N. A. M. Visser  W. van der Wal  E. J. O. Schrama  J. van den IJssel  J. Bouman 《Journal of Geodesy》2014,88(11):1029-1046

An assessment has been made of the possibility to estimate time-variable gravity from GPS-derived orbit perturbations and common-mode accelerometer observations of ESA’s GOCE Earth Explorer. A number of 20-day time series of Earth’s global long-wavelength gravity field have been derived for the period November 2009 to November 2012 using different parameter setups and estimation techniques. These techniques include a conventional approach where for each period, one set of gravity coefficients is estimated, either excluding or including empirical accelerations, and the so-called Wiese approach where higher frequency coefficients are estimated for the very long wavelengths. A principal component analysis of especially the time series of gravity field coefficients obtained by the Wiese approach and the conventional approach with empirical accelerations reveals an annual signal. When fitting this annual signal directly through the time series, the sine component (maximum in spring) displays features that are similar to well-known continental hydrological mass changes for the low latitude areas, such as mass variations in the Amazon basin, Africa and Australia for spatial scales down to 1,500 km. The cosine component (maximum in winter), however, displays large signals that can not be attributed to actual mass variations in the Earth system. The estimated gravity field changes from GOCE orbit perturbations are likely affected by missing GPS observations in case of high ionospheric perturbations during periods of increased solar activity, which is minimal in Summer and maximal towards the end of autumn.  相似文献   

On the relation between weather-related disaster impacts,vulnerability and climate change   总被引：1，自引：0，他引：1  

Hans Visser  Arthur C. Petersen  Willem Ligtvoet 《Climatic change》2014,125(3-4):461-477

Disasters such as floods, storms, heatwaves and droughts can have enormous implications for health, the environment and economic development. In this article, we address the question of how climate change might have influenced the impact of weather-related disasters. This relation is not straightforward, since disaster burden is not influenced by weather and climate events alone—other drivers are growth in population and wealth, and changes in vulnerability. We normalized disaster impacts, analyzed trends in the data and compared them with trends in extreme weather and climate events and vulnerability, following a 3 by 4 by 3 set-up, with three disaster burden categories, four regions and three extreme weather event categories. The trends in normalized disaster impacts show large differences between regions and weather event categories. Despite these variations, our overall conclusion is that the increasing exposure of people and economic assets is the major cause of increasing trends in disaster impacts. This holds for long-term trends in economic losses as well as the number of people affected. We also found similar, though more qualitative, results for the number of people killed; in all three cases, the role played by climate change cannot be excluded. Furthermore, we found that trends in historic vulnerability tend to be stable over time, despite adaptation measures taken by countries. Based on these findings, we derived disaster impact projections for the coming decades. We argue that projections beyond 2030 are too uncertain, not only due to unknown changes in vulnerability, but also due to increasing non-stationarities in normalization relations.  相似文献   

Innovating the IPCC review process—the potential of young talent     

Lianne van der Veer  Hans Visser  Arthur Petersen  Peter Janssen 《Climatic change》2014,125(2):137-148

There is significant potential in young talent for enhancing the credibility of the scientific assessments such as the IPCC’s by contributing to quality assurance and quality control. In this essay, we reflect on an experiment that was done by the Dutch government as part of its government review of a contribution to the IPCC’s Fifth Assessment Report (AR5). In an effort to review the entire Working Group II contribution to the AR5 within the official review period for the Second Order Draft (SOD), the PBL Netherlands Environmental Assessment Agency turned to PhD students. This article shows that a systematic review focusing on transparency and errors of a large scientific assessment document using young talented scientists can be successful if certain conditions are met. The reviewers need to have intrinsic motivation to conduct the review. There needs to be a communication plan that fosters engagement and a clear methodology to guide the reviewers through their task. Based on this experiment in review, we reflect on the wider potential for openness and crowdsourcing in scientific assessment processes such as the IPCC’s.  相似文献   

Energy integral method for gravity field determination from satellite orbit coordinates   总被引：22，自引：1，他引：21  

P. N. A. M. Visser  N. Sneeuw  C. Gerlach 《Journal of Geodesy》2003,77(3-4):207-216

A fast iterative method for gravity field determination from low Earth satellite orbit coordinates has been developed and implemented successfully. The method is based on energy conservation and avoids problems related to orbit dynamics and initial state. In addition, the particular geometry of a repeat orbit is exploited by using a very efficient iterative estimation scheme, in which a set of normal equations is approximated by a sparse block-diagonal equivalent. Recovery experiments for spherical harmonic gravity field models up to degree and order 80 and 120 were conducted based on a 29-day simulated data set of orbit coordinates. The method was found to be very flexible and could be easily adapted to include observations of non-conservative accelerations, such as (to be) provided by satellites like CHAMP, GRACE, and GOCE. A serious drawback of the method is its large sensitivity to satellite velocity errors. Existing orbit determination strategies need to be altered or augmented to include algorithms that focus on optimizing the accuracy of estimated velocities.  相似文献   

Logistic innovation in global supply chains: an empirical test of dynamic transaction-cost theory     

Evert-Jan Visser 《GeoJournal》2007,70(2-3):213-226

Upgrading logistic services in the context of international supply chains is not a smooth process. Upgrading may require the development of co-operative relationships, or alliances, involving large logistic service firms and their customers: multinational enterprises. Both sides may be unwilling and/or unable to engage in upgrading strategies in an alliance context. Fourth-party logistics is an example of a logistic product innovation entailing research-based advice as well as the design and implementation of new supply-chain solutions. It has the potential of stimulating spatial shift in global production networks and regional distribution systems (Visser and Lambooy, Geographisches Zeitschrift 92(heft 1+2):5–20, 2005). Using dynamic transaction-cost theory (Nooteboom, Learning and innovation in organisations and economies, 2000), this paper theoretically specifies and empirically measures three risks associated with the development of fourth-party logistics: dependence, unwanted spillovers, and conservatism. Case-study evidence reveals that dynamic transaction-cost theory partially explains the slow development of new logistic services in an alliance setting. Some aspects of conservatism are found to be relevant, along with risks of dependence due to specific investments in human resources and information systems. Other, not predicted but important factors, however, are the lack of credibility of service innovation by asset-based logistic firms, and strategic considerations of customers regarding logistic organization and control. The first factor implies that firms specializing in fourth-party services are likely to remain (very) limited in number. The second factor implies that this type of service provision is more likely to develop in dynamic port clusters, as customers prefer to tap into a variety of ideas from many different suppliers. In local clusters, interactions between firms can be relatively frequent, casual, short-lived and open, so that the structure of local networks is relatively decentralized, dense and flexible. This stimulates (logistic) innovation (Nooteboom, in Hanusch and Pyka (eds.) Elgar companion to neo Schumpeterian economics, 2006). In global supply chains, interactions between logistic service firms and their customers tend to have the opposite characteristics, which do not stimulate innovation.  相似文献   

TOPEX/Poseidon orbit error assessment   总被引：1，自引：0，他引：1  

A. J. E. Smith  E. T. Hesper  D. C. Kuijper  G. J. Mets  P. N. A. M. Visser  B. A. C. Ambrosius  K. F. Wakker 《Journal of Geodesy》1996,70(9):546-553

This paper discusses the accuracy of TOPEX/Poseidon orbits computed at Delft University, Section Space Research & Technology (DUT/SSR&T), from several types of tracking data,i.e. SLR, DORIS, and GPS. To quantify the orbit error, three schemes are presented. The first scheme relies on the direct altimeter observations and the covariance of the JGM-2 gravity field. The second scheme is based on crossover difference residuals while the third scheme uses the differences of dynamic orbit solutions with the GPS reduced-dynamic orbit. All three schemes give comparable results and indicate that the radial orbit error of TOPEX/Poseidon is 3–4 cm. From the orbit comparisons with GPS reduced dynamic, both the along-track and cross-track errors of the dynamic orbit solutions were found to be within 10–15 cm.  相似文献   

The homonormalisation of white heterosexual leisure spaces in Bloemfontein, South Africa     

Gustav Visser   《Geoforum》2008,39(3):1347-1361

The paper comprises a response to the overwhelming lack of geographical research into South African gay male leisure space development and augments the first detailed analyses of white gay leisure space development in this country by redirecting the geographic focus to a smaller provincial city. The image of gay leisure space that emerges in Bloemfontein is different from those identified and described in large metropolitan complexes. What emerges in this city is the development of gay-coded spaces in which heterosexual leisure spaces are queered, but not with the intent or outcome of generating exclusively gay spaces. Homonormalised spaces are created. It is contended that much of the current debates approach the so-called homonormalistion of gay leisure space from an unhelpful “gay/queer-disempowered” perspective which is inadequate to explain the development of a range of leisure spaces certain gay/queer cohorts created and/or seek out. It is suggested that homonormalised spaces are far more than heteronormativity infiltrating the gay (leisure) world through a range of consumption-led processes/events, or gay male capitulation to such normative hegemonies. It is argued that “homonormalisation” should be understood more reflexively.  相似文献   

Exploring the possibilities for star-tracker assisted calibration of the six individual GOCE accelerometers   总被引：1，自引：0，他引：1  

P. N. A. M. Visser 《Journal of Geodesy》2008,82(10):591-600

A method has been developed and tested for estimating calibration parameters for the six accelerometers on board the Gravity field and steady-state Ocean Circulation Explorer (GOCE) from star tracker observations. These six accelerometers are part of the gradiometer, which is the prime instrument on board GOCE. It will be shown that by taking appropriate combinations of observations collected by the accelerometers, by modeling acceleration terms caused by gravity gradients from an a priori low-degree spherical harmonic expansion, and by modeling rotational acceleration terms derived from star-tracker observations, scale factors of each of the accelerometers can be estimated for each axis. Simulated observations from a so-called end-to-end simulator were used to test the method. This end-to-end simulator includes a detailed model of the GOCE satellite, its instruments and instrument errors, and its environment. Results of the tests indicate that scale factors of all six accelerometers can be determined with an accuracy of around 0.01 for all components on a daily basis.  相似文献   

Algal bioassays: their significance in monitoring water quality with respect to nutrients and toxicants     

Pierre Couture  Simon A. Visser  Raymond van Coillie  Christian Blaise 《Aquatic Sciences - Research Across Boundaries》1985,47(2):127-158

The review focuses on the use of primary producers as a biological tool for evaluating the impact of damage by human activity (eutrophication, toxicity) on the aquatic environment. Studies are discussed following a reductionist approach by using algal bioassays (Selenastrum capricornutum). Variations of algal growth potential (AGP) within watersheds show the impact of human activities such as agriculture and urbanization, on water quality. The study of variation of the AGP in time allowed the investigation of the effect of abiotic (temperature, flow rate) and biotic factors (indigenous primary production) on the concentration of nutrients potentially available to phytoplankton. Seasonal changes of the AGP have further shown the impact of non-point (runoff) or point sources (sewage effluents) on the aquatic system. A staggered relationship was observed between AGP values and chlorophyll a content of indigenous phytoplankton. Values obtained in the laboratory by means of this type of approach would therefore appear to be transferably to natural systems. S. capricornutum was also used to identify toxic characteristics of substances (in pure form or used in formulations) and effluents released into the environment. It was shown that the user of bioassays should use care when evaluating results from tests requiring pretreatment such as storage, autoclaving and filtration. Cautious interpretation is also recommended in order to distinguish between effects of growth-limiting essential elements and the presence of toxic substances. In general it appears from this review that the AGP provides helpful information for a sound management of the aquatic environment.  相似文献