<abstract><title style='display:none'>Abstract</title>Digital Elevation Models (DEMs) comprise valuable source of elevation data required for many engineering applications. Contour lines, slope - aspect maps are part of their many uses. Moreover, DEMs are used often in geographic information systems (GIS), and are the most common basis for digitally-produced relief maps. This paper proposes a method of generating DEM by using Google Earth elevation data which is easier and free. The case study consisted of three different small regions in the northern beach in Egypt. The accuracy of the Google earth derived elevation data are reported using root mean square error (RMSE), mean error (ME) and maximum absolute error (MAE). All these accuracy statistics were computed using the ground coordinates of 200 reference points for each region of the case study. The reference data was collected with total station survey. The results showed that the accuracies for the prepared DEMs are suitable for some certain engineering applications but inadequate to meet the standard required for fine/small scale DEM for very precise engineering study. The obtained accuracies for terrain with small height difference can be used for preparing large area cadastral, city planning, or land classification maps.In general, Google Earth elevation data can be used only for investigation and preliminary studies with low cost. It is strongly concluded that the users of Google Earth have to test the accuracy of elevation data by comparing with reference data before using it.</abstract>

Investigation of the Accuracy of Google Earth Elevation Data

<abstract><title style='display:none'>ABSTRACT</title> The GNSS standard positioning solution determines the coordinates of the GNSS receiver and the receiver clock offset from measurements of at least four pseudoranges. For GNSS positioning, a direct solution was derived for five and ten observed satellites without linearisation of the observation equations and application of the least squares method. The article presents the basic principles of methods for solving the positioning problem, the formulas and their derivation. The numerical examples with simulated pseudorange data confirm the correct performance of the proposed algorithm. The presented algorithms should be further tested with real measurements in other domains of positioning and navigation as well.</abstract>

GNSS positioning algorithms using methods of reference point indicators

<abstract xml:lang="en"><title style='display:none'>The Lambda Method for the GNSS Compass</title>Global Navigation Satellite System carrier phase ambiguity resolution is the key to high precision positioning and attitude determination. In this contribution we consider the GNSS compass model. We derive the integer least-squares estimators and discuss the various steps involved in the ambiguity resolution process. This includes the method that has successfully been used in (<italic>Park and Teunissen</italic>, 2003). We emphasize the unaided, single frequency, single epoch case, since this is considered the most challenging mode of GNSS attitude determination.</abstract>

The Lambda Method for the GNSS Compass

<abstract><title style='display:none'>ABSTRACT</title>How to accelerate signal acquisition and shorten starting time are key problems in the Global Positioning System (GPS). GPS satellite almanac plays an important role in signal reception period. Almanac accuracy directly affects the speed of GPS signal acquisition, the start time of the receiver, and even the system performance to some extent. Combined with precise ephemeris products released by the International GNSS Service (IGS), the authors analyse GPS satellite almanac from the first day to the third day in the 1805th GPS week (from August 11 to 13, 2014 in the Gregorian calendar). The results show that mean of position errors in three-dimensional coordinate system varies from about 1 kilometer to 3 kilometers, which can satisfy the needs of common users.</abstract>

Positional Accuracy of Gps Satellite Almanac

<abstract><title style='display:none'>Abstract</title>Each GNSS constellation operates its own system times; namely, GPS system time (GPST), GLONASS system time (GLONASST), BeiDou system time (BDT) and Galileo system time (GST). They could be traced back to Coordinated Universal Time (UTC) scale and are aligned to GPST. This paper estimates the receiver clock offsets to three timescales: GPST, GLONASST and BDT. The two measurement scenarios use two identical multi-GNSS geodetic receivers connected to the same geodetic antenna through a splitter. One receiver is driven by its internal oscillators and another receiver is connected to the external frequency oscillators, caesium frequency standard, kept as the Thailand standard time scale at the National Institute of Metrology (Thailand) called UTC(NIMT). The three weeks data are observed at 30 seconds sample rate. The receiver clock offsets with respected to the three system time are estimated and analysed through the geodetic technique of static Precise Point Positioning (PPP) using a data processing software developed by Wuhan University - Positioning And Navigation Data Analyst (PANDA) software. The estimated receiver clock offsets are around 32, 33 and 18 nanoseconds from GPST, GLONASST and BDT respectively. This experiment is initially stated that each timescale is inter-operated with GPST and further measurements on receiver internal delay has to be determined for clock comparisons especially the high accuracy clock at timing laboratories.</abstract>

Precise Receiver Clock Offset Estimations According to Each Global Navigation Satellite Systems (GNSS) Timescales

<abstract xml:lang="en"><title style='display:none'>The Benefits of Inclined-Orbit Operations for Geostationary Orbit Communication Satellites</title>Geostationary orbit (GEO) communication satellites can be extended in lifetime by switching to inclined-orbit operations. In this mode, a small amount of propellant is reserved to maintain the assigned orbit longitude. Inclination is allowed to build up at a rate of approximately 0.8○ per year. Developing these space resources can bring out a number of benefits. Besides communication application, these satellites can be used to construct navigation constellation of the Chinese Area Positioning System (CAPS). In this present paper, the realization way of communication and navigation applications is studied and the benefits and problems are explained.</abstract>

The Benefits of Inclined-Orbit Operations for Geostationary Orbit Communication Satellites

<abstract>
<title style='display:none'>Abstract</title>
<italic>In situ</italic> resource utilization (ISRU) activities are receiving increasing attention, both from space agencies and among the international science and industrial community. Prominent examples of ongoing ISRU space programs are the NASA Artemis program and the Terrae Novae program run by the European Space Agency. In technical sciences, there are at least three groups of activities related to ISRU: prospecting bodies in the context of space missions, technological investigations related to surface infrastructure and operations, and conceptual analyses of future mining activities. The present paper belongs to the third group and brings new insights into a potential open pit mine operating on the Moon. There are several novel contributions: the definition of the objectives of the mine, based on economic indicators; a conceptual description of a pit architecture dedicated to excavating ilmenite-rich feedstock; and a qualitative and quantitative description of the chosen processes and the mine’s topology. In the paper, there are also added links to other papers connected with ISRU activities.
</abstract>

A Conceptual Open Pit Mine Architecture for the Moon Environment

<abstract>
<title style='display:none'>Abstract</title>
Nowadays, space debris is one of the main subjects of discussion regarding satellites in Earth's orbit. Right now, there are about 26,000 orbiting satellites and only few of these satellites are operational. Recently, the Polish space sector has been strongly growing and delivering instruments working in space. The first part of this paper describes the several space instruments designed in the Space Research Centre Polish Academy of Science (SRC PAS). Instruments such as SWI, RPPWI, LPPWI, Ebox or Pre-boxes have been created for a mission to Jupiter named “JUICE”. After fulfilling their scientific mission, these instruments can increase the amount of debris in space. This is one of the reasons for taking up the topic of space debris reduction and the use of technical solutions used in this mission for the proposed solution presented later.
The second part of this paper describes the new methods related to space debris. The activities can be related to the space debris removal programmes. The paper describes two methods developed by Polish scientists used for removal of space debris. One of them is the new capture method and mechanism designed for it. The special mechanism is based on tubular boom application for opening the net, to capture the space debris. The main parts of the mechanism are mechanisms which have been used in the JUICE space mission. The paper describes the main idea for these new methods, and for the design part prepared the strength confirmation by structural analysis. The main function of the mechanism has been verified by simulations and tests performed in laboratories.
</abstract>

Space Debris Capture - About New Methods of Tethered Space Net Opening by Tubular Booms

<abstract>
<title style='display:none'>Abstract</title>
This paper presents an R-based approach to mapping dynamics of the flooded areas in the Inner Niger Delta (IND), Mali, using time series analysis of Landsat 8–9 satellite images. As the largest inland wetland in West Africa, the habitats of IND offers high potential for biodiversity of the flood-dependent eco systems. IND is one of the most productive areas in West Africa. Mapping flooded areas based on satellite images enables to provide strategies for land management and rice planting and modelling vegetation types of IND. Our approach is based on using libraries of R programming language for processing six Landsat images, and each image was taken on November from 2013 to 2022. By capturing spatial and temporal structures of the satellite images on 2013, 2015, 2018, 2020, 2021 and 2022, the remote sensing data are combined to yield estimates of landscape dynamics that is temporally coherent, while helping to analyse fluctuations of spatial extent in fluvial wetlands caused by the hydrological processes of seasonal flooding. Further, by allowing packages of R to support image processing, an approach to mapping vegetation by NDVI, SAVI and EVI indices and visualising changes in distribution of different land cover classes over time is realised. In this context, processing Earth observation data by advanced scripting tools of R language provides new insights into complex interlace of climate-hydrological processes and vegetation responses. Our study contributes to the sustainable management of natural resources and improving knowledge on the functioning of IND ecosystems in Mali, West Africa.
</abstract>

Time Series Analysis of Landsat Images for Monitoring Flooded Areas in the Inner Niger Delta, Mali

<abstract>
<title style='display:none'>Abstract</title>
Our research aims to evaluate the triple-frequency GPS/Galileo/BeiDou kinematic precise point positioning (PPP) accuracy for the international maritime organization (IMO) positioning accuracy and integrity requirements. The real-time Centre National d’Etudes Spatiales (CNES) satellite orbit and clock products are used to simulate real-time scenarios. GPS/Galileo/BeiDou observations are collected from a moving vessel. Both dual-frequency and triple-frequency ionosphere-free PPP models are developed. Different satellite system combinations are used, including GPS-only, GPS/Galileo, GPS/BeiDou, and GPS/Galileo/BeiDou. The GPS-only differential solution is used as a reference. It is found that both dual- and triple-frequency kinematic PPP solutions achieve the IMO accuracy requirements at 95% confidence level for ocean, coastal, port approach, port, inland waterways, and track control navigation applications, except the automatic docking application. Moreover, the PPP solutions fulfilled the IMO integrity requirements for all navigation phase applications, but the GPS and GPS/BeiDou PPP solutions did not fulfill the automatic docking integrity requirement.
</abstract>

Evaluation of Triple-Frequency GPS/Galileo/Beidou Kinematic Precise Point Positioning Using Real-Time CNES Products for Maritime Applications

<abstract>
<title style='display:none'>Abstract</title>
Global Navigation Satellite Systems (GNSSs) are one of the techniques that can be used for the deformation monitoring caused by earthquakes. GNSSs enable the monitoring of specific areas affected by earthquakes in real-time and post-processing modes. This paper provides a novel method for the short-term displacement detection based on the phase residuals of GNSS observations. The study examines a natural earthquake from October 26, 2016, in Italy with Mw 6.1. In the proposed methodology, the residuals of the GNSS phase observations are derived using Precise Point Positioning. Then, residuals are transformed to the frequency domain using a wavelet transform, and the earthquake moment is identified using the anomalies detected in the scalogram, which do not appear in stable conditions. The described methodology allows for detecting the starting and ending moments of the earthquake. The methods described detected that the moment of the earthquake is visible in the residues 8 seconds after the seismic catalog time. The conducted experiments show that the use of signal analysis tools allows it to properly detect the ground vibrations in the residuals of GNSS phase observations and thus confirms the registration of ground vibrations in satellite observation data recorded by a GNSS receiver.
</abstract>

Using GNSS Phase Observation Residuals and Wavelet Analysis to Detect Earthquakes

<abstract>
<title style='display:none'>Abstract</title>
In this paper, the results of the orbit determination of two Chinese rocket bodies from low earth orbit (LEO) regime based on the picosecond laser measurements provided by one laser sensor are presented. A new approach was implemented that involved using a set of single laser measurements known as full-rate measurements instead of normal points. The computation strategy was applied using three different scenarios, and several key parameters such as root mean square (RMS), RMS of position (RMSPOS), RMS of velocity (RMSVEL), and alert time were determined. The results obtained indicate that the most optimal solution is to use short orbital arcs that are 24 h long. In this case, the average RMSPOS is approximately 345–530 m, the average RMSVEL is approximately 1 m/s, and the average arc RMS is approximately 3.7–7.0 cm. The determined alert time parameter, which refers to the time during which the laser observation of a given object should be repeated, is on average approximately 19.5 h.
If longer orbital arcs, such as 2 days or more, are used, RMSPOS and RMSVEL actually reach the level of single centimeters and single millimeters per second, respectively. However, the arc RMS increases significantly to at least decimeters and even above 1 m in some cases. This suggests that the long arc approach is not a favorable solution.
In addition, an interesting discovery has been presented that some Chinese launchers are equipped likely with the laser retroreflectors that can easily reflect the laser beam.
</abstract>

Orbit Determination of Chinese Rocket Bodies from the Picosecond Full-Rate Laser Measurements

<abstract xml:lang="en"><title style='display:none'>A General Multivariate Formulation of the Multi-Antenna GNSS Attitude Determination Problem</title>Global Navigation Satellite System (GNSS) carrier phase ambiguity resolution is the key to high precision positioning, navigation and attitude determination. In this contribution we present a general formulation for the multi-antenna GNSS attitude determination problem. This multivariate formulation provides a general framework for solving various GNSS attitude determination problems. With the use of this formulation we show how the constrained integer least-squares carrier phase ambiguities and corresponding attitude matrix can be solved.</abstract>

A General Multivariate Formulation of the Multi-Antenna GNSS Attitude Determination Problem

<abstract><title style='display:none'>ABSTRACT</title> Google Earth is a virtual globe, map and geographical information program that is controlled by Google corporation. It maps the Earth by the superimposition of images obtained from satellite imagery, aerial photography and GIS 3D globe. With millions of users all around the globe, GoogleEarth® has become the ultimate source of spatial data and information for private and public decision-support systems besides many types and forms of social interactions. Many users mostly in developing countries are also using it for surveying applications, the matter that raises questions about the positional accuracy of the Google Earth program. This research presents a small-scale assessment study of the positional accuracy of GoogleEarth® Imagery in Riyadh; capital of Kingdom of Saudi Arabia (KSA). The results show that the RMSE of the GoogleEarth imagery is 2.18 m and 1.51 m for the horizontal and height coordinates respectively.</abstract>

College of Engineering, Aswan University, Aswan, Egypt

College of Engineering, King Saud University, Riyadh, KSA

Positional Accuracy Assessment of Googleearth in Riyadh

<abstract><title style='display:none'>Abstract</title> On April 1, 2013 IGS launched the real-time service providing products for Precise Point Positioning (PPP). The availability of real-time makes PPP a very powerful technique to process GNSS signals in real-time and opens a new PPP applications opportunities. There are still, however, some limitations of PPP, especially in the kinematic mode. A significant change in satellite geometry is required to efficiently de-correlate troposphere delay, receiver clock offset, and receiver height. In order to challenge PPP limitations, the GNSS-WARP (Wroclaw Algorithms for Real-time Positioning) software has been developed from scratch at Wroclaw University of Environmental and Life Science in Poland. This paper presents the GNSS-WARP software itself and some results of GNSS data analysis using PPP and PPP-RTK (Real-Time Kinematic) technique. The results of static and kinematic processing in GPS only and GPS + GLONASS mode with final and real-time products are presented. Software performance validation in postprocessing mode confirmed that the software can be considered as a state-ofthe- art software and used for further studies on PPP algorithm development. The real-time positioning test made it possible to assess the quality of real-time coordinates, which is a few millimeters for North, East, Up in static mode, a below decimeter in kinematic mode. The accuracy and precision of height estimates in kinematic mode were improved by constraining the solution with an external, near real-time troposphere model. The software also allows estimation of real-time ZTD, however, the obtained precision of 11.2 mm means that further improvements in the software, real-time products or processing strategy are required.</abstract>

GNSS-Warp Software for Real-Time Precise Point Positioning

<abstract xml:lang="en"><title style='display:none'>Sensitivity of Lageos Orbits to Global Gravity Field Models</title>Precise orbit determination is an essential task when analyzing SLR data. The quality of the satellite orbits strongly depends on the models used for dynamic orbit determination. The global gravity field model used is one of the crucial elements, which has a significant influence on the satellite orbit and its accuracy. We study the impact of different gravity field models on the determination of the LAGEOS-1 and -2 orbits for data of the year 2008. Eleven gravity field models are compared, namely JGM3 and EGM96 based mainly on SLR, terrestrial and altimetry data, AIUB-CHAMP03S based uniquely on GPS-measurements made by CHAMP, AIUB-GRACE03S, ITG-GRACE2010 based on GRACE data, and the combined gravity field models based on different measurement techniques, such as EGM2008, EIGEN-GL04C, EIGEN51C, GOCO02S, GO-CONS-2-DIR-R2, AIUB-SST. The gravity field models are validated using the RMS of the observation residuals of 7-day LAGEOS solutions. The study reveals that GRACE-based models have the smallest RMS values (i.e., about 7.15 mm), despite the fact that no SLR data were used to determine them. The coefficient C20 is not always well estimated in GRACE-only models. There is a significant improvement of the gravity field models based on CHAMP, GRACE and GOCE w.r.t. models of the pre-CHAMP era. The LAGEOS orbits are particularly sensitive to the long wavelength part of the gravity fields. Differences of the estimated orbits due to different gravity field models are noticeable up to degree and order of about 30. The RMS of residuals improves from about 40 mm for degree 8, to about 7 mm for the solutions up to degrees 14 and higher. The quality of the predicted orbits is studied, as well.</abstract>

Sensitivity of Lageos Orbits to Global Gravity Field Models

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Artificial Satellites

The Journal of Space Research Centre of Polish Academy of Sciences

 Artificial Satellites is a journal of planetary geodesy, affiliated to the Space Research Centre, Polish Academy of Sciences. It offers a forum for scientific publications on such aspects of...

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 Artificial Satellites is a journal of planetary geodesy, affiliated to the Space Research Centre, Polish Academy of Sciences. It offers a forum for...

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