An evaluation of some systematic error sources affecting terrestrial gravity anomalies

Terrestrial free-air gravity anomalies form a most essential data source in the framework of gravity field determination. Gravity anomalies depend on the datums of the gravity, vertical, and horizontal networks as well as on the definition of a normal gravity field; thus gravity anomaly data are affected in a systematic way by inconsistencies of the local datums with respect to a global datum, by the use of a simplified free-air reduction procedure and of different kinds of height system. These systematic errors in free-air gravity anomaly data cause systematic effects in gravity field related quantities like e.g. absolute and relative geoidal heights or height anomalies calculated from gravity anomaly data. In detail it is shown that the effects of horizontal datum inconsistencies have been underestimated in the past. The corresponding systematic errors in gravity anomalies are maximum in mid-latitudes and can be as large as the errors induced by gravity and vertical datum and height system inconsistencies. As an example the situation in Australia is evaluated in more detail: The deviations between the national Australian horizontal datum and a global datum produce a systematic error in the free-air gravity anomalies of about −0.10 mgal which value is nearly constant over the continent     

Single epoch ambiguity resolution for Galileo with the CAR and LAMBDA methods

This paper investigates single epoch ambiguity resolution performance using Galileo four frequency data. Two commonly used ambiguity resolution methods are used in the tests, including the Cascade Ambiguity Resolution (CAR) and the Least-Squares Ambiguity Decorrelation Adjustment (LAMBDA) methods. For CAR method, four optimal combinations are carefully selected according to their wavelength to noise ratios and success rate for ambiguity fixing. The test results show, in general, the LAMBDA method performs better than the CAR method. The speed of ambiguity resolution is closely related to the carrier phase measurement precision. With carrier phase measurement precision of 3 mm, single epoch ambiguity resolution can be achieved at every epoch with simulated 1-s interval 24-h Galileo data (total epochs 86,400). With the increase of carrier phase noise, ambiguity resolution performances become worse. When the noise level is increased to 12 mm, single epoch ambiguity resolution can only be achieved about 50% of epochs.     

An evaluation of measures for quantifying map information

A real-time map must not contain too much information. Therefore, we need measures of map information that could be guidelines for the selection of data layers and the real-time generalisation process. In this paper we evaluate measures of the amount of information and the distribution of information. The evaluation is performed by (1) defining measures, (2) implementing the measures, (3) computing the measures for some test maps, and finally (4) comparing the values of the measures with human judgement of the map information. For amount of information, we found that the measures number of objects, number of points and object line length had better correspondence with human judgement than object area. We also found that measures based on the size of Voronoi regions of objects (respectively points) can be used for identifying the distribution of information. The results are based on the testing of only building objects. Future work should extend the test, using all object types.     

An evaluation of solar radiation pressure strategies for the GPS constellation

The subtle effects of different Global Positioning System (GPS) satellite force models are becoming apparent now that mature processing strategies are reaching new levels of accuracy and precision. For this paper, we tested several approaches to solar radiation pressure (SRP) modeling that are commonly used by International GNSS Service (IGS) analysis centers. These include the GPS Solar Pressure Model (GSPM; Bar-Sever and Kuang in The Interplanetary Network Progress Report 42-160, 2005) and variants of the so-called DYB model (Springer et al. in Adv Space Res 23:673–676, 1999). Our results show that currently observed differences between GPS orbit solutions from the various IGS analysis centers are in large part explained by differences between their respective approaches to modeling SRP. DYB-based strategies typically generate orbit solutions that have the smallest differences with respect to the IGS final combined solution, largely because the DYB approach is most commonly used by the contributing analysis centers. However, various internal and external metrics, including ambiguity resolution statistics and satellite laser ranging observations, support continued use of the GSPM-based approach for precise orbit determination of the GPS constellation, at least when using the GIPSY-OASIS software.     

An evaluation of integrating multisourced sensors for disaster management

Disaster management and in particular disaster response phase are highly time-sensitive and dynamic processes, demanding that real-time information reaches disaster responders prior making critical decisions. During the last decade, disaster management has been widely enabled through utilizing spatial data sourcing and related technologies in the whole process of collection, access, and usage of disaster information. Currently, there are unique challenges that cannot be met without incorporating in situ sensing as an emerging technology for sourcing and managing disaster information. These include (1) high temporal and spatial resolution of information, (2) broad range of disaster data, and (3) automated operations. Incorporating in situ sensing into the disaster management process can potentially address such challenges by providing data that support all of these requirements. Following an examination of current concepts and methods for integrating multisourced sensors, a framework of the requirements for integrating in situ sensors for disaster management, is suggested. Based on this framework and its components, an evaluation of the methods is developed and applied. The results highlight that information integration of multisourced sensors is a major challenge and has not yet adequately addressed for sensor data enablement of disaster management.     

W0: an estimate in the Finnish Height Datum N60, epoch 1993.4, from twenty-five GPS points of the Baltic Sea Level Project

Based upon a data set of 25 points of the Baltic Sea Level Project, second campaign 1993.4, which are close to mareographic stations, described by (1) GPS derived Cartesian coordinates in the World Geodetic Reference System 1984 and (2) orthometric heights in the Finnish Height Datum N60, epoch 1993.4, we have computed the primary geodetic parameter W ₀(1993.4) for the epoch 1993.4 according to the following model. The Cartesian coordinates of the GPS stations have been converted into spheroidal coordinates. The gravity potential as the additive decomposition of the gravitational potential and the centrifugal potential has been computed for any GPS station in spheroidal coordinates, namely for a global spheroidal model of the gravitational potential field. For a global set of spheroidal harmonic coefficients a transformation of spherical harmonic coefficients into spheroidal harmonic coefficients has been implemented and applied to the global spherical model OSU 91A up to degree/order 360/360. The gravity potential with respect to a global spheroidal model of degree/order 360/360 has been finally transformed by means of the orthometric heights of the GPS stations with respect to the Finnish Height Datum N60, epoch 1993.4, in terms of the spheroidal “free-air” potential reduction in order to produce the spheroidal W ₀(1993.4) value. As a mean of those 25 W ₀(1993.4) data as well as a root mean square error estimation we computed W ₀(1993.4)=(6 263 685.58 ± 0.36) kgal × m. Finally a comparison of different W ₀ data with respect to a spherical harmonic global model and spheroidal harmonic global model of Somigliana-Pizetti type (level ellipsoid as a reference, degree/order 2/0) according to The Geodesist's Handbook 1992 has been made. Received: 7 November 1996 / Accepted: 27 March 1997     

An evaluation of unsupervised and supervised learning algorithms for clustering landscape types in the United States

Knowledge of landscape type can inform cartographic generalization of hydrographic features, because landscape characteristics provide an important geographic context that affects variation in channel geometry, flow pattern, and network configuration. Landscape types are characterized by expansive spatial gradients, lacking abrupt changes between adjacent classes; and as having a limited number of outliers that might confound classification. The US Geological Survey (USGS) is exploring methods to automate generalization of features in the National Hydrography Data set (NHD), to associate specific sequences of processing operations and parameters with specific landscape characteristics, thus obviating manual selection of a unique processing strategy for every NHD watershed unit. A chronology of methods to delineate physiographic regions for the United States is described, including a recent maximum likelihood classification based on seven input variables. This research compares unsupervised and supervised algorithms applied to these seven input variables, to evaluate and possibly refine the recent classification. Evaluation metrics for unsupervised methods include the Davies–Bouldin index, the Silhouette index, and the Dunn index as well as quantization and topographic error metrics. Cross validation and misclassification rate analysis are used to evaluate supervised classification methods. The paper reports the comparative analysis and its impact on the selection of landscape regions. The compared solutions show problems in areas of high landscape diversity. There is some indication that additional input variables, additional classes, or more sophisticated methods can refine the existing classification.     

Vertical accuracy evaluation of SRTM-GL1, GDEM-V2, AW3D30 and CartoDEM-V3.1 of 30-m resolution with dual frequency GNSS for lower Tapi Basin India

Abstract

Shuttle Radar Topography Mission (SRTM-GL1), Advanced Space Borne Thermal Emission and Reflection Radiometer- Global DEM (GDEM-V2), recently released Advanced Land Observing Satellite (‘DAICHI’) DEM (AW3D30) and Indian National Cartosat-1 DEM v3 (CartoDEM-V3.1) provide free topographic data at a 30-m resolution for Indian peninsula. In this research study, the vertical accuracy of DEM is evaluated for above data-sets and compared with high accuracy dual frequency GNSS of a millimetre accuracy. The extensive field investigation is carried out using a stratified random fast static DGPS survey for collecting 117 high accuracy ground control points in a predominantly agriculture catchment. Further, the effect of land cover, slope and low-lying coastal zone on DEM vertical accuracy was also analysed and presented in this study.     

An evaluation of Guided Regularized Random Forest for classification and regression tasks in remote sensing

New Earth observation missions and technologies are delivering large amounts of data. Processing this data requires developing and evaluating novel dimensionality reduction approaches to identify the most informative features for classification and regression tasks. Here we present an exhaustive evaluation of Guided Regularized Random Forest (GRRF), a feature selection method based on Random Forest. GRRF does not require fixing a priori the number of features to be selected or setting a threshold of the feature importance. Moreover, the use of regularization ensures that features selected by GRRF are non-redundant and representative. Our experiments based on various kinds of remote sensing images, show that GRRF selected features provides similar results to those obtained when using all the available features. However, the comparison between GRRF and standard random forest features shows substantial differences: in classification, the mean overall accuracy increases by almost 6% and, in regression, the decrease in RMSE almost reaches 2%. These results demonstrate the potential of GRRF for remote sensing image classification and regression. Especially in the context of increasingly large geodatabases that challenge the application of traditional methods.     

An evaluation of Radarsat-2 individual and combined image dates for land use/cover mapping

Various land use/cover types exhibit seasonal characteristics which can be captured in remotely sensed imagery. This study examined how different seasons of Radarsat-2 data influence land use/cover classification accuracies for two study sites. Two dates of Radarsat-2 C-band quad-polarised images were obtained for Washington, DC, USA and Wad Madani, Sudan. Spectral signatures were extracted and used with a maximum likelihood decision rule for classification and thematic accuracies were then determined. Both despeckled radar and derived texture measures were examined. Thematic accuracies for the two despeckled image dates were similar with a difference of 3% for Washington and 6% for Sudan. Merging the despeckled images for both seasons increased overall accuracy by 2% for Washington and 9% for Sudan. Further combining the original radar for both seasons with derived texture measures increased overall accuracies by 9% for Washington and 16% for Sudan for final overall accuracy values of 73 and 82%.     

An evaluation of sampling and full enumeration strategies for Fisher Jenks classification in big data settings

Large data contexts present a number of challenges to optimal choropleth map classifiers. Application of optimal classifiers to a sample of the attribute space is one proposed solution. The properties of alternative sampling‐based classification methods are examined through a series of Monte Carlo simulations. The impacts of spatial autocorrelation, number of desired classes, and form of sampling are shown to have significant impacts on the accuracy of map classifications. Tradeoffs between improved speed of the sampling approaches and loss of accuracy are also considered. The results suggest the possibility of guiding the choice of classification scheme as a function of the properties of large data sets.     

An evaluation of remote sensing derived soil pH and average spring groundwater table for ecological assessments

Ecological assessments such as species distribution modelling and benchmarking site quality towards regulations often rely on full spatial coverage information of site factors such as soil acidity, moisture regime or nutrient availability. To determine if remote sensing (RS) is a viable alternative to traditional data sources of site factor estimates, we analysed the accuracy (using ground truth validation measurements) of traditional and RS sources of pH and mean spring groundwater level (MSL, in m) estimates. Traditional sources were a soil map and hydrological model. RS estimates were obtained using vegetation indicator values (IVs) from a Dutch national system as an intermediate between site factors and spectral response. IVs relate to those site factors that dictate vegetation occurrence, whilst also providing a robust link to canopy spectra. For pH, the soil map and the RS estimate were nearly as accurate. For MSL, the RS estimates were much closer to the observed groundwater levels than the hydrological model, but the error margin of the estimates still exceeded the tolerance range of moisture sensitive vegetation. The relatively high accuracy of the RS estimates was made possible by the availability of local calibration points and large environmental gradients in the study site. In addition, the error composition of the RS estimates could be analysed step-by-step, whereas the traditional sources had to be accepted ‘as-is’. Also considering that RS offers high spatial and temporal resolution at low costs, RS offered advantages over traditional sources. This will likely hold true for any other situation where prerequisites of accurate RS estimates have been met.     

An evaluation of supervised classifiers for indirectly detecting salt-affected areas at irrigation scheme level

Soil salinity often leads to reduced crop yield and quality and can render soils barren. Irrigated areas are particularly at risk due to intensive cultivation and secondary salinization caused by waterlogging. Regular monitoring of salt accumulation in irrigation schemes is needed to keep its negative effects under control. The dynamic spatial and temporal characteristics of remote sensing can provide a cost-effective solution for monitoring salt accumulation at irrigation scheme level. This study evaluated a range of pan-fused SPOT-5 derived features (spectral bands, vegetation indices, image textures and image transformations) for classifying salt-affected areas in two distinctly different irrigation schemes in South Africa, namely Vaalharts and Breede River. The relationship between the input features and electro conductivity measurements were investigated using regression modelling (stepwise linear regression, partial least squares regression, curve fit regression modelling) and supervised classification (maximum likelihood, nearest neighbour, decision tree analysis, support vector machine and random forests). Classification and regression trees and random forest were used to select the most important features for differentiating salt-affected and unaffected areas. The results showed that the regression analyses produced weak models (<0.4 R squared). Better results were achieved using the supervised classifiers, but the algorithms tend to over-estimate salt-affected areas. A key finding was that none of the feature sets or classification algorithms stood out as being superior for monitoring salt accumulation at irrigation scheme level. This was attributed to the large variations in the spectral responses of different crops types at different growing stages, coupled with their individual tolerances to saline conditions.     

The ideas of Mr. Dupuy about the use and future arrangement of tables of correlatives

Zusammenfassung Die Ideen und Anregungen, die der Ingenieur-Geograph Dr. MichelDupuy, Paris, hinsichtlich der vielseitigen Verwendungsm?glichkeiten von Korrelatentabellen (Tafeln der Kehrmatrizen von Winkelnormalgleichungs-Systemen) in der geod?tischen Praxis an dieser Stelle ver?ffenllicht hat, werden ebenso lebhaft begrü?t wie seine Vorschl?ge zur weiteren Verfolgung des vonBoltz, Friedrich, Marcantoni und dem Verfasser eingeschlagenen Weges. Stellungnahme zu den Anregungen im einzelnen. Vorschlag eines Gedankenauslausches zwischen den interessierten Fachleulen verschiedener Nationalit?t.

---

The ideas of Mr. Dupuy about the use and future arrangement of tables of correlatives

Summary The author deals with the ideas of Dr. MichelDupuy (Paris), concerning the future arrangement of tables of correlatives (tables of inverse matrices of angle equation systems) and their use in practical theoretical work published in this periodical. Following the author, the proposals of Dr.Dupuy, referred in detail, are of high value and exchange of ideas between interested specialists of different nationality seems to be worth of consideration.

---

Resumen El autor discute las ideas de Mr.Dupuy (Paris) relativas a la confección de las tablas de correlativas (matrices inversas de las matrices de las ecuaciones de ángulos) y a su uso desde el punto de vista práctico y teórico. Según el autor, las propuestas de Mr.Dupuy son muy importantes y los cambios de ideas entre especialistas de los diferentes paises merecerian ser examinadas.

---

Sommario L'A. discute le idee del Sig.Dupuy (Parigi) relative alla costruzione di tavole di correlativi (matrici inverse delle matrici delle equazioni agli angoli) ed il loro uso dal punto di vista pratico e teoretico. Secondo l'A. le considerazioni del Sig.Dupuy sono importantissime e gli scambi d'idee tra specialisti di differenti Paesi meritano incoraggiamento.

     

Assessing the suitability of GlobeLand30 for mapping land cover in Germany

Global land cover (LC) maps have been widely employed as the base layer for a number of applications including climate change, food security, water quality, biodiversity, change detection, and environmental planning. Due to the importance of LC, there is a pressing need to increase the temporal and spatial resolution of global LC maps. A recent advance in this direction has been the GlobeLand30 dataset derived from Landsat imagery, which has been developed by the National Geomatics Center of China (NGCC). Although overall accuracy is greater than 80%, the NGCC would like help in assessing the accuracy of the product in different regions of the world. To assist in this process, this study compares the GlobeLand30 product with existing public and online datasets, that is, CORINE, Urban Atlas (UA), OpenStreetMap, and ATKIS for Germany in order to assess overall and per class agreement. The results of the analysis reveal high agreement of up to 92% between these datasets and GlobeLand30 but that large disagreements for certain classes are evident, in particular wetlands. However, overall, GlobeLand30 is shown to be a useful product for characterizing LC in Germany, and paves the way for further regional and national validation efforts.     

《中国改革开放30年地图集》选题研究与创意设计

紧紧围绕"纪念改革开放30年"这一主题,对展示内容的设计和地图表现方法进行了深入的研究与实践,总结出一套行之有效的设计思想,可供类似工作参考.     

Experience with the ULISS-30 inertial survey system for local geodetic and cadastral network control

The capability of the recently developed SAGEM ULISS-30 inertial survey system for performing local surveys at high accuracies have been tested in a field campaign carried out November 1989 on the island of Fyn, Denmark, in cooperation with the Swedish National Land Survey. In the test a number of lines between existing national geodetic control points were surveyed, along with points in the less reliably determined cadastral network, forming an irregular network pattern of 10–15 km extent. The survey involved frequent offset measurements (up to 50–100 m) with an ISS-integrated total station. The profile geometries were not particularly suited for inertial surveys, with narrow and rather winding roads, necessitating frequent vehicle turns. In addition to the pure inertial surveys a kinematic GPS/inertial test was also carried out, using a pair of Ashtech L-XII receivers. The inertial survey results, analyzed with a smoothing algoritm utilizing common points on forward/backward runs, indicate that 5-cm accuracies are possible on reasonably straight profiles of 5 km length, corresponding to a 10 ppm best-case accuracy for double-run traverses. On longer, more winding traverses error levels of 10–20 cm are typical. To handle the inertial data optimally, proper network adjustments are required. A discussion of suitable adjustment models of both conventional and collocation type is included in the paper.     

城市总体规划实施评估的大数据技术集成创新探索 ——以珠海为例

以大数据技术在珠海城市总体规划实施评估中的集成应用为实例,总结了城市总体规划实施评估的5项大数据关键技术,梳理了涉及用地、人口、空间格局、交通体系、公共服务、绿地系统等多个专项的大数据分析模块,探索形成了一套大数据支撑的城市总体规划实施评估理论方法与分析技术集成体系。     

An evaluation of potential solar radio emission power threat on GPS and GLONASS performance

The L-band solar radio emission has recently been regarded as a potential threat to stable GPS and GLONASS performance. However, the threat has not been completely investigated or assessed so far. We evaluate in detail the occurrence of GPS/GLONASS signal tracking failures under the direct exposure of wideband solar radio emission. By means of theoretical analysis, we found that the solar radio emission power level of 1,000?sfu (solar flux units) or higher can cause GPS/GLONASS signal tracking failures especially at L2 frequency. In order to prove this evaluation, we investigated GPS/GLONASS signal tracking failures at L1 and L2 frequencies during power solar flares X6.5 (December 6, 2006) and X3.4 (December 13, 2006). Comparing these events with weaker solar flare X17.2 on October 28, 2003, we found that L2 signal tracking failures appeared when the solar radio emission power exceeds 1,000?sfu. Therefore, our theoretical and experimental results confirm the earlier results by other authors.