Effect of heteroscedasticity and heterogeneousness on outlier detection for geodetic networks

The robustness of an outlier detection method strongly depends on the weights of observations, i.e., the type of the stochastic model applied (homoscedasticity, heteroscedasticity and heterogeneousness). In this paper, we have investigated how the reliability of the robust methods and tests for outliers changes depending on the weights of the observations in geodetic networks. Furthermore, the contribution of the directions and distances to horizontal control network with regard to reliability are investigated separately. The concept of a breakdown point is used as a global measure of robustness against outliers. The mean success rate (MSR) is found to be a practical tool for confirming the breakdown point. Many different “good” data samples are generated for each network and then deliberately contaminated using a Monte-Carlo simulation. Six robust methods and Baarda’s test are applied to the corrupted samples and the degree of corruption is varied. The performance of each method is measured using both local and global MSRs. Our research shows: (1) The MSRs of Baarda’s test change depending on the strength of the heteroscedasticity, but do not change for trilateration and leveling networks, (2) the global MSRs of robust methods do not differ considerably from the local ones     

三种GNSS模糊度解算方法成功率比较

介绍了在航模糊度求解的模型。在航模型每个历元均需要多估计一组坐标矢量,因而降低模糊度求解的精度。用取整法、引导取整法和整数最小二乘法三种模糊度固定方法,比较了在静态模型和在航模型下整周模糊度求解的成功率和需要的初始化时间,为动态平台的糊度解算提供参考。     

Congruent,decreasing trends of gentoo penguins and Crozet shags at sub-Antarctic Marion Island suggest food limitation through common environmental forcing

Numbers of gentoo penguins Pygoscelis papua and Crozet shags Phalacrocorax [atriceps] melanogenis breeding annually at Marion Island, one of South Africa's Prince Edward Islands in the South-West Indian Ocean, were strongly correlated over 19 split-years from 1994/1995 to 2012/2013. Both species decreased between the mid-1990s and the mid-2000s, exhibited a partial recovery in the late-2000s and then decreased to their lowest recorded levels in 2012/2013. In both instances, the partial recoveries in the late-2000s were associated with improved breeding success. At a colony of gentoo penguins, breeding success was negatively correlated with the date of arrival of adults to breed. Gentoo penguins and Crozet shags are demersal feeders in inshore waters around Marion Island and there is considerable overlap in the composition of their diets. Therefore, trends in their populations may be driven by food availability, which is likely to be influenced by benthic production around the island. We propose that, in South Africa, and based on the current assessment, the Crozet shag, which elsewhere breeds only at the Crozet Islands, is now Critically Endangered, and the more widely ranging gentoo penguin is Endangered.     

Invasion of Sargassum muticum in intertidal rockpools: Patterns along the Atlantic Iberian Peninsula

Spatial patterns of non-indigenous species show scale-dependent properties. Sargassum muticum is an invasive macroalga widely distributed along the Atlantic Iberian Peninsula. Despite being quite abundant from Norway to South Portugal, there is little information about its patterns of distribution, particularly at a large spatial scale (i.e. thousands of kilometres). Here, we examined the spatial variation in the invasion success of S. muticum from rockpools at multiple spatial scales using a hierarchical design. In addition, we analysed how the richness of native assemblages was related to its invasion success and how this relationship changed over different scales. Most of the variation in the invasion success was found at the smallest scales of pool and plot. Furthermore, the invasibility of native macroalgal assemblages was related to the native species richness, but causes that determined invasion success could not be separated from the effects provoked by the invader. Results suggest that small-scale (centimetres to metres) processes contribute considerably to the heterogeneity of S. muticum invasion success.     

Long-term community changes on a high-latitude coral reef in the Greater St Lucia Wetland Park, South Africa

South African coral reefs are limited in size but, being marginal, provide a model for the study of many of the stresses to which these valuable systems are being subjected globally. Soft coral cover, comprising relatively few species, exceeds that of scleractinians over much of the reefs. The coral communities nevertheless attain a high biodiversity at this latitude on the East African coast. A long-term monitoring programme was initiated in 1993, entailing temperature logging and image analysis of high resolution photographs of fixed quadrats on representative reef. Sea temperatures rose by 0.15 degrees C p.a. at the site up to 2000 but have subsequently been decreasing by 0.07 degrees C p.a. Insignificant bleaching was encountered in the region during the 1998 El Nino Southern Oscillation (ENSO) event, unlike elsewhere in East Africa, but quantifiable bleaching occurred during an extended period of warming in 2000. Peak temperatures on the South African reefs thus appear to have attained the coral bleaching threshold. While this has resulted in relatively little bleaching thus far, the increased temperatures appear to have had a deleterious effect on coral recruitment success as other anthropogenic influences on the reefs are minimal. Recruitment success diminished remarkably up to 2004 but appears again to be improving. Throughout, the corals have also manifested changes in community structure, involving an increase in hard coral cover and reduction in that of soft corals, resulting in a 5.5% drop in overall coral cover. These "silent" effects of temperature increase do not appear to have been reported elsewhere in the literature.     

一种综合利用像方和物方信息的多影像匹配方法

A novel method for multi-image matching by synthesizing image and object-space information is proposed. Firstly, four levels of image pyramids are generated according to the rule that the next pyramid level is generated from the previous level using the average gray values of the 3 by 3 pixels, and the first level of pyramid image is generated from the original image. The initial horizontal parallaxes between the reference image and each searching image are calculated at the highest level of the image pyramid. Secondly, corresponding image points are searched in each stereo image pair from the third level of image pyramid, and the matching results in all stereo pairs are integrated in the object space, by which the mismatched image points can be eliminated and more accurate spatial information can be obtained for the subsequent pyramid image matching. The matching method based on correlation coefficient with geometric constraints and global relaxation matching is introduced in the process of image matching. Finally, the feasibility of the method proposed in this paper is verified by the experiments using a set of digital frame aerial images with big overlap. Compared with the traditional image matching method with two images, the accuracy of the digital surface model (DSM) generated using the proposed method shows that the multi-image matching method can eliminate the mismatched points effectively and can improve the matching success rate significantly. Supported by the National Natural Science Foundation of China (Nos. 40771176, 40721001).     

无先验信息的改进目标函数单历元模糊度正确率分析

基于CA码和双频载波相位信息建立双差伪距和宽巷相位观测模型以浮点变换方法生成模糊度备选空间将改进的目标函数L1相位残差平方和与L2相位残差平方和之和替换传统的目标函数浮点解与真解残差二次型作为模糊度搜索的准则18h实测静态数据的计算结果表明在模糊度求解的正确率可靠性和可用性方面改进的目标函数优于传统的目标函数.     

北斗星上多径对宽巷模糊度解算的影响分析

通过引入北斗星上多径参数,量化了北斗星上多径对宽巷模糊度解算的影响;从理论上分析了该影响量在非差、单差和双差条件下的特性,并采用零基线、短基线和长基线3组实测数据进行了分析与验证。结果表明:星上多径对非差宽巷模糊度估值的影响在三类卫星上表现出不同的特性,在MEO卫星上最大,可达1周;星间单差无法消除星上多径偏差影响,进而PPP宽巷模糊度的解算将受到影响;星上多径不会对零基线双差宽巷模糊度解算造成影响,对短基线双差宽巷模糊度解算的影响也可忽略,但长基线双差宽巷模糊度解算则受严重影响;星上多径会导致长基线双差宽巷模糊度平滑收敛缓慢,经改正后模糊度固定成功率能够显著提高,单历元取整成功率从52.7%提升到61.4%,平滑20个历元模糊度固定成功率即可从68.4%提升到95.5%。     

Addition of Phosphorus and Nitrogen Support the Invasiveness of Alternanthera Philoxeroides Under Water Stress

Coordination of plant functional traits with changes in the environment is helpful to understand the mechanisms underlying both invasiveness and adaptation of plants. Thus, to investigate the performance and functional traits in invasive Alternanthera philoxeroides (Mart.), an experiment of water stress is conducted with different nutrient concentrations. Alternanthera philoxeroides plants are grown under natural and nutrient soils and subjected to three levels of nitrogen (N) and phosphorus (P) solution: ambient P and N concentration (P?N?), P addition with an ambient N concentration (P+N?), and P addition with high N concentration (P+N+) in combination with three different irrigation water levels as 1) 100% irrigation, 2) 50% irrigation, and 3) 25% deficit irrigation. Based on results, A. philoxeroides produces significantly higher biomass in both soils under 100% irrigation with P+N? treatment and exhibits higher values of leaf area and root length. However, 25% irrigation with P?N? treatment in both soils exerts a significant negative effect on relative growth rate and root/shoot ratio of A. philoxeroides plants. Under 50% irrigation in soils with both P+N? and P+N+ treatments, high values of leaf nitrogen are recorded. Moreover, nutrient soil is more supportive to A. philoxeroides than natural soil.     

Calanoid copepod resting egg abundance and hatching success in the sediment of the Seine estuary (France)

Benthic, viable resting eggs of calanoid copepods were found for the first time in the Seine estuary (France) during July 2008. Vertical distribution of the resting eggs in the sediment was determined up to 10 cm depth. Hatching success of the eggs extracted from different 1-cm thick sediment layers was experimentally tested immediately after extraction and after a long refractory phase (i.e. 11 months) of storage at low temperature (4–5 °C). The hatching success of resting eggs obtained immediately after sediment incubation was lower (0.72%) than the value observed after 11 months (4.50%) with an overall hatching success of 2.37%. The marine, calanoid copepod Temora longicornis was the primary species to hatch from the eggs; however, the estuarine calanoid copepod Eurytemora affinis also hatched from resting eggs. The mean abundance of eggs found in sediment (1.42 × 10⁶ eggs m⁻²) was comparable to that reported for other marine and estuarine calanoid copepods. The Seine estuary sediment had a high variability of egg abundance (between 0.14 and 8.10 × 10⁷ eggs m⁻³) suggesting that the hydrodynamics of this macrotidal estuary are likely responsible for this variability. Significant sediment resuspension occurs in the Seine estuary during flood periods and spring tides leading to resting eggs to contribute along the year to the nauplii recruitment of calanoid copepods. On average, around 400,000 nauplii m⁻³ month⁻¹ of the main calanoid copepods can emerge from the surface layer sediment in the Seine estuary, suggesting that resting eggs could play an important role in the population dynamics of key calanoid copepods in the Seine estuary.