A New Orbiting Deployable System for Small Satellite Observations for Ecology and Earth Observation

In this paper, we present several study cases focused on marine, oceanographic, and atmospheric environments, which would greatly benefit from the use of a deployable system for small satellite observations. As opposed to the large standard ones, small satellites have become an effective and affordable alternative access to space, owing to their lower costs, innovative design and technology, and higher revisiting times, when launched in a constellation configuration. One of the biggest challenges is created by the small satellite instrumentation working in the visible (VIS), infrared (IR), and microwave (MW) spectral ranges, for which the resolution of the acquired data depends on the physical dimension of the telescope and the antenna collecting the signal. In this respect, a deployable payload, fitting the limited size and mass imposed by the small satellite architecture, once unfolded in space, can reach performances similar to those of larger satellites. In this study, we show how ecology and Earth Observations can benefit from data acquired by small satellites, and how they can be further improved thanks to deployable payloads. We focus on DORA—Deployable Optics for Remote sensing Applications—in the VIS to TIR spectral range, and on a planned application in the MW spectral range, and we carry out a radiometric analysis to verify its performances for Earth Observation studies

The EGNOS Augmentation in Maritime Navigation

The objective of this work is the evaluation of the performances of EGNOS (European Geostationary Navigation Overlay System) augmentation system in maritime navigation by comparing them with those obtained by other positioning methods as Single Point Positioning (SPP) and Differential Global Positioning System (DGPS). Preliminarily, EGNOS performances in an open-sky context were evaluated through static data downloaded by EGNOS RIMS (Ranging and Integrity Monitoring Stations) located in Rome. Then, for the maritime test carried out onboard a boat in the Gulf of Naples, two dual-frequency receivers were used: Xiaomi Mi 8 smartphone and u-blox ZED-F9P multi-band GNSS (Global Navigation Satellite System) receiver, both in kinematic mode. At last, IMO (International Maritime Organization) requirements, established in IMO Resolution A.1046 (27), that a SBAS (Satellite Based Augmentation System) system in particular scenarios (coastal, inland-water, harbor navigation and ocean waters) must respect, were verified

A proposed fault detection and exclusion method applied to multi-GNSS single-frequency PPP

In the last few years, Precise Point Positioning (PPP) has become widespread as a standalone positioning technique. Unlike classical GNSS point positioning, which uses the pseudorange observables from four or more visible satellites and the broadcast ephemeris to obtain the user instantaneous position, PPP takes the advantage of the more precise carrier phase measurements, attempting to account for all the GNSS errors and biases. PPP is able to provide accuracy level comparable to differential positioning. In particular, the single-frequency (SF) PPP technique is attracting great interest, since SF GNSS devices are widely used for most positioning and navigation applications. For this aim, the paper proposes a SF-PPP approach based on the use of code and single-frequency ionosphere-free linear observables combination, collected from GPS and Galileo systems. In addition, an integrity monitoring algorithm is modified to be applied to SF-PPP for the detection, isolation and the removal of faulty measurement sources. The proposed strategy is tested using real and simulated data gathered in static mode. Results demonstrate the effectiveness of the proposed integrity monitoring algorithm, applied to SF-PPP

Usporedba performansi među tehnikama preciznog pozicioniranja s jednofrekvencijskim višestrukim GNSS-om https://doi.org/10.32909/kg.18.32.6

Precise Point Positioning (PPP) is a technique able to compute high accuracy positioning anywhere using a single GNSS receiver and without the need for corrections from reference stations. A wide range of possible PPP algorithms, using different correction models and processing strategies, exist for both post-processing and real-time applications. PPP relies on accurate satellite and clock data, with the use of precise carrier-phase measurements. Single Frequency-PPP (SF-PPP) is currently under investigation by the scientific community, owing to its cheap implementation with respect to classical differential positioning and multi-frequency un-differenced techniques.Unfortunately, the carrier-phase observable is ambiguous by an a priori unknown integer number of cycles, called ambiguity, which is difficult to resolve with SF receivers. The aim of this paper was to study the opportunity provided by the use of a multi-GNSS constellation applied to two widespread SF-PPP models, based on different carrier-phase and code observable combinations. The algorithms were tested using static data collection carried out in an open-sky scenario. The results show decimeter level accuracy on the horizontal and vertical components of the position.Precizno pozicioniranje točke (Precise Point Positioning – PPP) je tehnika koja je u mogućnosti bilo gdje izračunati vrlo precizno pozicioniranje koristeći se jednim prijamnikom GNSS-a bez potrebe za ispravkama referentnih stanica. Postoji širok raspon algoritama za PPP s različitim modelima korekcije i strategije obrade, kako za primjene nakon obrade, tako i za one u stvarnom vremenu. PPP ovisi o točnim podatcima satelita i sata, uz upotrebu preciznih mjerenja faze nosača. Znanstvena zajednica trenutačno ispituje jednofrekvencijski PPP (SF-PPP) zahvaljujući njegovoj jeftinoj primjeni u odnosu na klasično diferencijalno pozicioniranje i višefrekvencijske nediferencirane tehnike.Nažalost, promatrana faza nosača dvosmislena je po apriorno nepoznatom cjelobrojnom broju ciklusa, nazvanom dvosmislenost (ambiguity), što je teško razriješiti s pomoću SF prijamnika. Cilj je ovog rada bio proučiti mogućnost koju daje konstelacija višestrukih GNSS-ova primjenom na dvama široko rasprostranjenim modelima SF-PPP, na temelju različitih faza nosača i opažanih kombinacija kodova. Algoritmi su testirani korištenjem statičkog prikupljanja podataka provedenog u scenariju s otvorenim nebom. Rezultati pokazuju decimetarsku točnost u horizontalnoj i vertikalnoj komponenti položaja

NeQuick Galileo version model: Assessment of a proposed version in operational scenario

The ionosphere is one of the main error sources for single-frequency Global Navigation Satellite System (GNSS) measurements in open-sky scenario. Most widespread GNSS devices are single frequency stand-alone receivers and they can use different Ionospheric Correction Algorithms (ICA) in order to reduce the ionospheric error. In this work two ICA models are considered, specifically Klobuchar and NeQuick-G models. These algorithms are driven by parameters broadcast within GPS and Galileo navigation messages respectively. Hence no additional infrastructure is needed to reduce the ionospheric effects. The main goal of the paper is to analyze the performance of a modified approach for NeQuick-G (defined NeQuick VP) by comparing its performance, in position domain, with respect to the standard NeQuick-G algorithm and to Klobuchar one. NeQuick VP is a methodology proposed to reduce the complexity characterizing NeQuick-G model. The performance is evaluated using real data collected by an open-sky station; the results obtained are analyzed using Root Mean Square (RMS), mean and maximum errors as Key Performance Indicators (KPIs) for both horizontal and vertical components

Robust Estimation Methods Applied to GPS in Harsh Environments

Satellite navigation is very widespread in civil society; many devices and services exploit this technology and several systems are in use or in development phase. GNSS receiver, embedded in devices used in daily life (smartphones, cars and so on), works in several conditions and operational scenarios. Ensuring good positioning accuracy is challenging, especially in environment where receiver measurements are affected by gross errors, such as urban canyons. In this paper, the benefit of robust estimators in case of multiple simultaneous blunders is investigated; several robust estimators were implemented and their performances are compared with classical techniques used in GNSS context (WLS, RAIM) using real data. Effectiveness of these methods raised from tests conducted in static and kinematic mode

Performance Comparison among Multi-GNSS Single Frequency Precise Point Positioning Techniques

Precizno pozicioniranje točke (Precise Point Positioning – PPP) je tehnika koja je u mogućnosti bilo gdje izračunati vrlo precizno pozicioniranje koristeći se jednim prijamnikom GNSS-a bez potrebe za ispravkama referentnih stanica. Postoji širok raspon algoritama za PPP s različitim modelima korekcije i strategije obrade, kako za primjene nakon obrade, tako i za one u stvarnom vremenu. PPP ovisi o točnim podatcima satelita i sata, uz upotrebu preciznih mjerenja faze nosača. Znanstvena zajednica trenutačno ispituje jednofrekvencijski PPP (SF-PPP) zahvaljujući njegovoj jeftinoj primjeni u odnosu na klasično diferencijalno pozicioniranje i višefrekvencijske nediferencirane tehnike. Nažalost, promatrana faza nosača dvosmislena je po apriorno nepoznatom cjelobrojnom broju ciklusa, nazvanom dvosmislenost (ambiguity), što je teško razriješiti s pomoću SF prijamnika. Cilj je ovog rada bio proučiti mogućnost koju daje konstelacija višestrukih GNSS-ova primjenom na dvama široko rasprostranjenim modelima SF-PPP, na temelju različitih faza nosača i opažanih kombinacija kodova. Algoritmi su testirani korištenjem statičkog prikupljanja podataka provedenog u scenariju s otvorenim nebom. Rezultati pokazuju decimetarsku točnost u horizontalnoj i vertikalnoj komponenti položaja.Precise Point Positioning (PPP) is a technique able to compute high accuracy positioning anywhere using a single GNSS receiver and without the need for corrections from reference stations. A wide range of possible PPP algorithms, using different correction models and processing strategies, exist for both post-processing and real-time applications. PPP relies on accurate satellite and clock data, with the use of precise carrier-phase measurements. Single Frequency-PPP (SF-PPP) is currently under investigation by the scientific community, owing to its cheap implementation with respect to classical differential positioning and multi-frequency un-differenced techniques. Unfortunately, the carrier-phase observable is ambiguous by an a priori unknown integer number of cycles, called ambiguity, which is difficult to resolve with SF receivers. The aim of this paper was to study the opportunity provided by the use of a multi-GNSS constellation applied to two widespread SF-PPP models, based on different carrier-phase and code observable combinations. The algorithms were tested using static data collection carried out in an open-sky scenario. The results show decimeter level accuracy on the horizontal and vertical components of the position

Fuzzy logic applied to GNSS

Limiting the weight of bad signals can recover the accuracy of the GNSS solution in signal-degraded scenarios, where multipath reflections and obstructions can easily generate multiple blunders. The fuzzy integration of the available information related to the quality of the received signals is exploited in this paper to derive an effective weighting schema in a Weighted Least Square estimation process. To validate the proposed schema, its performance in the position domain is compared to the most common weighting strategies proposed in the literature, based on GPS data collected through two different High Sensitivity GNSS receivers placed in urban canyons and processed in Single Point Positioning using pseudorange measurements

The EGNOS Augmentation in Maritime Navigation

The objective of this work is the evaluation of the performances of EGNOS (European Geostationary Navigation Overlay System) augmentation system in maritime navigation by comparing them with those obtained by other positioning methods as Single Point Positioning (SPP) and Differential Global Positioning System (DGPS). Preliminarily, EGNOS performances in an open-sky context were evaluated through static data downloaded by EGNOS RIMS (Ranging and Integrity Monitoring Stations) located in Rome. Then, for the maritime test carried out onboard a boat in the Gulf of Naples, two dual-frequency receivers were used: Xiaomi Mi 8 smartphone and u-blox ZED-F9P multi-band GNSS (Global Navigation Satellite System) receiver, both in kinematic mode. At last, IMO (International Maritime Organization) requirements, established in IMO Resolution A.1046 (27), that a SBAS (Satellite Based Augmentation System) system in particular scenarios (coastal, inland-water, harbor navigation and ocean waters) must respect, were verified

Reliability testing for multiple GNSS measurement outlier detection

Due to a rapid development of several Global Navigation Satellite Systems (GNSS), multiple constellations are available to enhance navigation performance and safety. With the growing number of satellite constellations, the task of the GNSS navigation is to deal with the differences among systems but, on the other hand, more great levels of integrity and satellite visibility can be expected. GNSS navigation applications have difficulties in signal degraded scenarios where the GNSS solution can be degraded by errors such as multipath and signals being obscured. RAIM (Receiver Autonomous Integrity Monitoring) is a method necessary for assessing integrity performance levels mainly in safety-critical applications. Classical RAIM techniques are based on the assumption model of a single outlier in the measurements, but with a future of higher satellite availability and for navigation conducted in urban canyon scenarios, the single outlier assumption is unrealistic. Therefore, reliability monitoring techniques need to be modified to be suitable for use cases with high signal degradation levels. The FDE (Fault Detection and Exclusion) schemes analysed in this research for reliability monitoring are the Observation Subset Testing and a modified approach based on a w-test (called in this paper Multiple Faults De-weighting-MFD). In order to improve their performance a novel Channel Quality Index (CQI) parameter was used to describe the measurement confidence and quality. To validate the proposed approaches, tests have been performed using simulated data with GPS, Galileo and BeiDou signals in a multipath environment