Automated cleaning and uncertainty attribution of archival bathymetry based on a priori knowledge

Hydrographic offices hold large valuable historic bathymetric data sets, many of which were collected using older generation survey systems that contain little or no metadata and/or uncertainty estimates. These bathymetric data sets generally contain large outlier (errant) data points to clean, yet standard practice does not include rigorous automated procedures for systematic cleaning of these historical data sets and their subsequent conversion into reusable data formats. In this paper, we propose an automated method for this task. We utilize statistically diverse threshold tests, including a robust least trimmed squared method, to clean the data. We use LOESS weighted regression residuals together with a Student-t distribution to attribute uncertainty for each retained sounding; the resulting uncertainty values compare favorably with native estimates of uncertainty from co-located data sets which we use to estimate a point-wise goodness-of-fit measure. Storing a cleansed validated data set augmented with uncertainty in a re-usable format provides the details of this analysis for subsequent users. Our test results indicate that the method significantly improves the quality of the data set while concurrently providing confidence interval estimates and point-wise goodness-of-fit estimates as referenced to current hydrographic practices.     

Impact of minimum legal size increases on egg‐per‐recruit production,size structure,and ovigerous females in the American lobster (Homarus americanus) population off the Magdalen Islands (Quebec,Canada): A case study

In the mid 1990s, American lobster (Homarus americanus) from Canadian waters was considered overfished based on estimated levels of egg‐per‐recruit production (EPR). In 1997, the Department of Fisheries Oceans responded by adopting a goal of doubling the level of EPR from its 1996 level. In the Magdalen Islands (Quebec), results from a simulation model indicated that doubling EPR could be reached by increasing the minimum legal size (MLS) from 76 mm to 83 mm carapace length. This was done at a pace of 1 mm per year from 1997 to 2003. Following the increase of MLS, the size structure, mean size, and the abundance of ovigerous females improved significantly in the catches. However, levels of fishing effort are still very high. This could cause undesirable effects such as altering sex ratios and size structure of males, which could lead to sperm limitation, and reducing the contribution of multiple spawners to egg production, which could become an issue if egg quality is important. Consideration of these issues leads to the recommendation of a multidimensional approach to lobster conservation.     

Boreal peatland margins as repository sites of long-term natural disturbances of balsam fir/spruce forests

A multidisciplinary, high-resolution paleoecological study (Lepidoptera and plant remains, macroscopic charcoal, pollen) was conducted on a 4000-yr peat monolith extracted from the margin of an ombrotrophic peatland on Anticosti Island (Gulf of St. Lawrence, eastern Canada) to reconstruct the long-term natural disturbances (insect outbreaks, forest fires) of a balsam fir/spruce forest. We hypothesized that an activity of insect defoliators (spruce budworm, hemlock looper) was the main disturbance factor of conifer forests during the Late Holocene. The earliest remains of spruce budworm and hemlock looper were found ca. 3220 and 2350 cal yr BP, respectively. Peaks of insect head capsules occurred from ca. 1640 to ca. 625 cal yr BP. Low balsam fir pollen concentrations during this period suggest a lengthy episode ( 1000 yr) of high insect activity, resulting in extensive fir dieback and mortality. The long-term dynamics of the pristine balsam fir/spruce forests were mainly governed by the activity of insect defoliators. The limited extent and possibly the low occurrence of forest fires in the maritime environment of Anticosti Island allowed the development of mature coniferous stands propitious for insect infestations. Insect head capsules appeared to be a useful and effective tool for establishing insect presence and activity during the Holocene.     

Fast and Accurate Approximation to Kriging Using Common Data Neighborhoods

Unknown values of a random field can be predicted from observed data using kriging. As data sets grow in size, the computation times become large. To facilitate kriging with large data sets, an approximation where the kriging is performed in sub-segments with common data neighborhoods has been developed. It is shown how the accuracy of the approximation can be controlled by increasing the common data neighborhood. For four different variograms, it is shown how large the data neighborhoods must be to get an accuracy below a chosen threshold, and how much faster these calculations are compared to the kriging where all data are used. Provided that variogram ranges are small compared to the domain of interest, kriging with common data neighborhoods provides excellent speed-ups (2–40) while maintaining high numerical accuracy. Results are presented both for data neighborhoods where the neighborhoods are the same for all sub-segments, and data neighborhoods where the neighborhoods are adapted to fit the data densities around the sub-segments. Kriging in sub-segments with common data neighborhoods is well suited for parallelization and the speed-up is almost linear in the number of threads. A comparison is made to the widely used moving neighborhood approach. It is demonstrated that the accuracy of the moving neighborhood approach can be poor and that computational speed can be slow compared to kriging with common data neighborhoods.     

Neural Network Prediction of Monthly Precipitation: Application to Summer Flood Occurrence in Two Regions of Central Europe

Artificial Neural Network (ANN) models were used to forecast precipitation. Three-layer back propagation ANNs were trained with actual monthly precipitation data from six Czech and four Hungarian meteorological stations for the period 1961-1998. The predicted amounts are the next month's precipitation. Both training and testing ANN results provided a good fit with the actual data and displayed high feasibility in predicting extreme precipitation.     

Fragmentation processes and xenolith transport in a Proterozoic minette dyke,Grenville Province,Québec

 The Mesoproterozoic Rivard minette dyke provides a case example of dyke-parallel fracturing induced by propagation of low-viscosity melts at deep crustal levels. The dyke constitutes a xenolith-choked intrusion breccia and provides samples of an extensive section of the lithosphere underlying the southwestern Grenville Province of Québec at 1.08 Ga. The xenoliths occupy approximately 50% of the volume of the breccia. They are extremely diverse and include pyroxenites and mafic granulites from the upper mantle and lower crust, and Grenvillian gabbroids, gneisses and quartzites. Wall-rock fragments are detached to various extents along dyke-parallel fractures and apophyses. The host lamprophyre magma has a calculated viscosity of ca. 40 Pa·s. Rapid ascent of magma and turbulence are suggested by the presence of large dense fragments and the brittle-to-ductile deformation at the margins of some xenoliths. A minimum ascent velocity of ca. 50 cm·s^–1 is estimated from the settling velocity of a 40 cm long pyroxenite xenolith. The progressive addition of xenoliths increased the effective viscosity of the liquid-solid mixture to 10³ Pa·s during emplacement. This favoured Bingham behaviour and laminar flow of the magma, and xenolith suspension. Field evidence suggests that xenoliths were formed through (1) early fracturing of wall rock by inelastic deformation during dyke propagation, and (2) continuous delamination of wall rock by intrusion of magma along the dyke-parallel fractures. This led to removal of chilled margins, and to fluid infiltration, partial melting and microbrecciation in the wall rock. Pre-existing discontinuities played a minor role in the fracturing process. Xenoliths may thus be abundant in alkaline magmas not only because these magmas ascend rapidly and can transport xenoliths, but possibly also, because their low viscosities promote intense fracturing of wall rock. Received: 10 June 1995 / Accepted: 10 February 1996     

Coronal heating

Louise Harra presents a summary of a meeting at which a wealth of new sources of data – Yohkoh, SOHO, TRACE, XMM-Newton and Chandra – is bringing new insights to studies of solar and stellar coronal heating.     

An Estimate of Eros's Porosity and Implications for Internal Structure

Earth-based spectral measurements and NEAR Shoemaker magnetometer, X-ray, and near-infrared spectrometer data are all consistent with Eros having a bulk composition and mineralogy similar to ordinary chondrite meteorites (OC). By comparing the bulk density of 433 Eros (2.67±0.03 g/cm³) with that of OCs (3.40 g/cm³), we estimate the total porosity of the asteroid to be 21-33%. Macro (or structural) porosity, best estimated to be ∼20%, is constrained to be between 6 and 33%. We conclude that Eros is a heavily fractured body, but we find no evidence that it was ever catastrophically disrupted and reaccumulated into a rubble pile.     

Applications Of Electrical And Electromagnetic Methods For Environmental And Geotechnical Investigations

Electrical and electromagnetic methods are powerful tools in environmentaland geotechnical investigations. Techniques developed for deeper applications, such as mining,geothermal and crustal studies, are scaled for shallow targets by moving to higher frequencies,earlier decay times and/or smaller array configurations. Another extremely important factor is dense stationspacing, to reduce spatial aliasing, and high quality data to resolve small features. Hence, new instrumentsare concerned with making continuous or dense measurements with high precision, and interpretationalmethods fast enough to handle large datasets quickly. Continuously measuring electrical and time-domainelectromagnetic systems have been developed for geological mapping in hydrological investigations withone-dimensional inversion routines that are rapid and robust. At a smaller scale an electrical systemis used for archaeology studies with excellent results. Working to and above the upper limits ofthe quasi-static approximation, a very early time electromagnetic system is proving successful at mapping subsurfaceinfrastructure in areas of conductive, clay cover, where ground penetrating radar is ineffective.Induced polarization (IP) and resistivity systems that employ multiplexing techniques, while not continuouslymeasuring, allow for relatively rapid production rates and dense sampling for applications ranging fromlandfill and contaminant characterization studies, to verifying the integrity of engineeredsubsurface structures and monitoring infiltration in the vadose zone.     

Theoretical and Al CPMAS NMR investigation of aluminum coordination changes during aluminosilicate dissolution

Ab initio molecular orbital calculations were performed, and ²⁷Al CP MAS-NMR spectra were evaluated in order to investigate the possible tetrahedral to octahedral coordination change of Al at the feldspar-water interface under acidic conditions. Aluminum coordination is octahedral in solution, and tetrahedral in feldspar crystals. Whether this change in coordination can occur on feldspar surfaces as part of the dissolution mechanism has been debated. Molecular orbital calculations were performed on aluminosilicate clusters with a few surrounding water molecules to partially account for solvation effects at the feldspar-water interface. The calculations on both fully-relaxed and partially-constrained clusters suggest that the energy difference between ^[4]Al and ^[6]Al where both are linked to three Si-tetrahedra (i.e., Q³ Al) in the feldspar structure, is small enough to allow for the conversion of Q^3[4]Al to Q^3[6]Al in a hydrated layer of feldspar, prior to the release of Al ions to the aqueous solution. The introduction of a few water molecules to the clusters introduced the possibility of multiple optimized geometries for each Al coordination, with energy differences on the order of several hydrogen bonds. The calculation of activation energies and transition states between Q^3[4]Al, Q^3[5]Al, and Q^3[6]Al was complicated by the introduction of water molecules and the use of fully-relaxed aluminosilicate clusters. Calculated isotropic shifts for Q^1[6]Al, Q^2[6]Al, and Q^3[6]Al suggest that the ^[6]Al observed on aluminosilicate glass surfaces using ²⁷Al CP MAS-NMR is Q^1[6]Al and therefore formed as part of the dissolution process. The formation of ^[6]Al in situ on a feldspar surface (as opposed to re-precipitation from solution) has significant implications for the dissolution mechanism and surface chemistry of feldspars.