A Low-Cost Global Navigation Satellite System Positioning Accuracy Assessment Method for Agricultural Machinery

The high-precision positioning and navigation of agricultural machinery represent a backbone for precision agriculture, while its worldwide implementation is in rapid growth. Previous studies improved low-cost global navigation satellite system (GNSS) hardware solutions and fused GNSS data with complementary sources, but there is still no affordable and flexible framework for positioning accuracy assessment of agricultural machinery. Such a low-cost method was proposed in this study, simulating the actual movement of the agricultural machinery during agrotechnical operations. Four of the most commonly used GNSS corrections in Croatia were evaluated in two repetitions: Croatian Positioning System (CROPOS), individual base station, Satellite-based Augmentation Systems (SBASs), and an absolute positioning method using a smartphone. CROPOS and base station produced the highest mean GNSS positioning accuracy of 2.4 and 2.9 cm, respectively, but both of these corrections produced lower accuracy than declared. All evaluated corrections produced significantly different median values in two repetitions, representing inconsistency of the positioning accuracy regarding field conditions. While the proposed method allowed flexible and effective application in the field, future studies will be directed towards the reduction of the operator’s subjective impact, mainly by implementing autosteering solutions in agricultural machinery.

Signal-to-Noise Ratio Analyses of Spaceborne GNSS-Reflectometry from Galileo and BeiDou Satellites

In recent years, Global Navigation Satellite System Reflectometry (GNSS-R) technology has made considerable progress with the increasing of GNSS-R satellites in orbit, the improvements of GNSS-R data processing technology, and the expansion of its geophysical applications. Meanwhile, with the modernization and evolution of GNSS systems, more signal sources and signal modulation modes are available. The effective use of the signals at different frequencies or from new GNSS systems can improve the accuracy, reliability, and resolution of the GNSS-R data products. This paper analyses the signal-to-noise ratio (SNR) of the GNSS-R measurements from Galileo and BeiDou-3 (BDS-3) systems, which is one of the important indicators to measure the quality of GNSS-R data. The multi-GNSS (GPS, Galileo and BDS-3) complex waveform products generated from the raw intermediate frequency data from TechDemoSat-1 (TDS-1) satellite and Cyclone Global Navigation Satellite System (CYGNSS) constellation are used for such analyses. The SNR and normalized SNR (NSNR) of the reflected signals from Galileo and BDS-3 satellites are compared to these from GPS. Preliminary results show that the GNSS-R SNRs from Galileo and BDS-3 are ∼1–2 dB lower than the GNSS-R measurements from GPS, which could be due to the power of the transmitted power and the bandwidth of the receiver. In addition, the effect of coherent integration time on GNSS-R SNR is also assessed for different GNSS signals. It is shown that the SNR of the reflected signals can be improved by using longer coherent integration time (∼0.4–0.8 dB with 2 ms coherent integration and ∼0.6–1.2 dB with 4 ms coherent integration). In addition, it is also shown that the SNR can be improved more efficiently (∼0.2–0.4 dB) for reflected BDS-3 and Galileo signals than for GPS. These results can provide useful references for the design of future spaceborne GNSS-R instrument compatible with reflections from multi-GNSS constellations.

Implantação de uma rede de aferição de equipamentos geodésicos e topográficos

O PRESENTE ARTIGO VERSA SOBRE A IMPLANTAÇÃO DE UMA REDE DE AFERIÇÃO DE INSTRUMENTOS TOPOGRÁFICOS E GEODÉSICOS, PARA QUE SEJA POSSÍVEL QUANTIFICAR E QUALIFICAR ERROS SISTEMÁTICOS APRESENTADOS POR TAIS EQUIPAMENTOS. NESSE CASO, HÁ A NECESSIDADE DE VERIFICAÇÃO DE RETIFICAÇÃO E DE CONTROLE SOBRE A PROPAGAÇÃO DO ERRO EM TRABALHOS DE COLETA DE DADOS. PARA ESSE PROPÓSITO, SERÃO UTILIZADOS MARCOS DE CENTRAGEM FORÇADA NÃO COLINEARES, CONSTRUÍDOS NA ÁREA EXPERIMENTAL DO CAMPUS DA UNIPAMPA, EM ITAQUI (RS). COM O INTUITO DE SE OBTER DADOS QUALITATIVOS DA REDE, CADA MARCO FOI RASTREADO POR RECEPTORES DA CONSTELAÇÃO CONSTITUINTE DO SISTEMA GLOBAL DE NAVEGAÇÃO POR SATÉLITE (GLOBAL NAVIGATION SATELLITE SYSTEM - GNSS). POSTERIORMENTE, ELES FORAM PÓS-PROCESSADOS PELO POSICIONAMENTO POR PONTO PRECISO (PPP), SERVIÇO ONLINE GRATUITO PARA PÓS-PROCESSAMENTO ABSOLUTO, A ¬FIM DE SE OBTER AS COORDENADAS GEODÉSICAS DE CADA VÉRTICE. OS VALORES DO RASTREIO TAMBÉM FORAM COMPARADOS AOS DADOS DE ÂNGULOS E DISTÂNCIAS (COORDENADAS POLARES) QUE SÃO MENSURADOS, A PARTIR DA ESTAÇÃO TOTAL. A ¬FIM DE MINIMIZAR ERROS SISTEMÁTICOS, METODOLOGIAS DOS PARES CONJUGADOS (DIRETA E INVERSA) EM VISADAS RECÍPROCAS, FORAM UTILIZADAS. NA SEQUÊNCIA, O AJUSTAMENTO DE OBSERVAÇÕES FOI APLICADO, UTILIZANDO-SE OS MÉTODOS DOS MÍNIMOS QUADRADOS (MMQ) (CORRELATO E PARAMÉTRICO), SENDO QUE O MÉTODO PARAMÉTRICO MOSTROU-SE MAIS APLICÁVEL NA REDE (MENORES RESÍDUOS). POR ¬FIM, OS RESULTADOS DOS ÂNGULOS E DISTÂNCIAS AJUSTADAS SERVEM COMO BASE PARA VERIFICAÇÃO DO ERRO LINEAR E ANGULAR, FUNDAMENTADOS NAS ESPECIFICAÇÕES TÉCNICAS DO INSTRUMENTO. PALAVRAS-CHAVE: REDE DE AFERIÇÃO. TOPOGRAFIA. GEODÉSIA.

Using CYGNSS Data to Map Flood Inundation during the 2021 Extreme Precipitation in Henan Province, China

On 20 July 2021, parts of China’s Henan Province received the highest precipitation levels ever recorded in the region. Floods caused by heavy rainfall resulted in hundreds of casualties and tens of billions of dollars’ worth of property loss. Due to the highly dynamic nature of flood disasters, rapid and timely spatial monitoring is conducive for early disaster prevention, mid-term disaster relief, and post-disaster reconstruction. However, existing remote sensing satellites cannot provide high-resolution flood monitoring results. Seeing as spaceborne global navigation satellite system-reflectometry (GNSS-R) can observe the Earth’s surface with high temporal and spatial resolutions, it is expected to provide a new solution to the problem of flood hazards. Here, using the Cyclone Global Navigation Satellite System (CYGNSS) L1 data, we first counted various signal-to-noise ratios and the corresponding reflectivity to surface features in Henan Province. Subsequently, we analyzed changes in the delay-Doppler map of CYGNSS when the observed area was submerged and not submerged. Finally, we determined the submerged area affected by extreme precipitation using the threshold detection method. The results demonstrated that the flood range retrieved by CYGNSS agreed with that retrieved by the Soil Moisture Active Passive (SMAP) mission and the precipitation data retrieved and measured by the Global Precipitation Measurement mission and meteorological stations. Compared with the SMAP results, those obtained by CYGNSS have a higher spatial resolution and can monitor changes in the areas affected by the floods over a shorter period.

Validation of the accuracy of geodetic automated measurement system based on GNSS platform for continuous monitoring of surface movements in post-mining areas

The problem involving the monitoring of surface ground movements in post-mining areas is particularly important during the period of mine closures. During or after flooding of a mine, mechanical properties of the rock mass may be impaired, and this may trigger subsidence, surface landslides, uplift, sinkholes or seismic activity. It is, therefore, important to examine and select updating methods and plans for long-term monitoring of post-mining areas to mitigate seismic hazards or surface deformation during and after mine closure. The research assumed the implementation of continuous monitoring of surface movements using the Global Navigation Satellite System (GNSS) in the area of a closed hard coal mine ‘Kazimierz-Juliusz’, located in Poland. In order to ensure displacement measurement results with the accuracy of several millimetres, the accuracy of multi-GNSS observations carried out in real time as a combination of four global navigation systems, Global Positioning System (GPS), Globalnaja Navigacionnaja Sputnikova Sistema (GLONASS), Galileo and BeiDou, was determined. The article presents the results of empirical research conducted at four reference points. The test observations were made in variants comprising measurements based on: GPS, GPS and GLONASS systems, GPS, GLONASS and Galileo systems, GPS, GLONASS, Galileo and BeiDou systems. For each adopted solution, daily measurement sessions were performed using the RTK technique. The test results were subjected to accuracy analyses. Based on the obtained results, it was found that GNSS measurements should be carried out with the use of three navigation systems (GPS, GLONASS, Galileo), as an optimal solution for the needs of continuous geodetic monitoring in the area of the study.

Prospective directions for the development of microwave frequency standards for satellite navigation systems

The state of essential various quantum standards of GNSS frequencies for today are collected and presented, the results of analysis in the direction of modernization of time synchronization systems in global navigation satellite systems are presented. The most perspective directions of modernization of global navigation satellite systems are mentioned – the development of new atomic clocks on the mercury ions -199. The data on experimental satellite gives encouraging results.