Design and performance analysis of advanced GNSS-R instruments back-end
GNSS reflectometry (GNSS-R) is a set of techniques that uses the reflected GNSS signals over the Earth’s surface as opportunity signals for remote sensing applications. In 1993, the European Space Agency (ESA) suggested to use those signals as a tool to estimate sea height anomalies in an attempt to...
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| Tipo de recurso: | tesis doctoral |
| Estado: | Versión publicada |
| Fecha de publicación: | 2020 |
| País: | España |
| Institución: | CBUC, CESCA |
| Repositorio: | TDR. Tesis Doctorales en Red |
| OAI Identifier: | oai:www.tdx.cat:10803/670632 |
| Acceso en línea: | http://hdl.handle.net/10803/670632 https://dx.doi.org/10.5821/dissertation-2117-337026 |
| Access Level: | acceso abierto |
| Palabra clave: | Àrees temàtiques de la UPC::Enginyeria de la telecomunicació 55 621.3 |
| Sumario: | GNSS reflectometry (GNSS-R) is a set of techniques that uses the reflected GNSS signals over the Earth’s surface as opportunity signals for remote sensing applications. In 1993, the European Space Agency (ESA) suggested to use those signals as a tool to estimate sea height anomalies in an attempt to detect tsunamis before they reach the shore. Since then, GNSS-R has been a subject of topical interest, and has proven its feasibility for a diverse number of applications in land, ice and water bodies, from ground-based, airborne and space-borne instruments. This Ph.D. thesis has its roots in the ESA project PARIS-IoD, which aimed to study the feasibility of GNSS-R for sea altimetry from a space-borne instrument. Unfortunately, the project was canceled shortly after starting this thesis. However, some of the questions that have arisen during the initial phase of the project, have been the goals of this Ph.D. The thesis has two objectives. The first one is to solve some theoretical issues required for the development of next generation of GNSS-R instruments. The second one is to participate in the development of an airborne GNSS-R instrument mimicking the one intended for the PARIS-IoD, and to use it in field campaigns. The main feature of this instrument is that it has two dual-band (L1/L5) array antennas, with two beams per band that are analog steered towards the desired satellite and reflection point. As for the theoretical objectives; this thesis investigates five topics. Firstly, the thesis gives closed-form expressions of the so-called Woodward Ambiguity Functions (WAFs) of the modern GNSS signals as function of the receiver bandwidth. The motivation behind this work is that these equations can be later used in simulators in order to create reference models based on different physical magnitudes. Secondly, the thesis finds the optimum receiver bandwidth for each GNSS signal in terms of altimetric precision. The idea behind this study is that using a large bandwidth produces sharper waveforms, which translates into a higher resolution. However, the thermal noise increases as well with the bandwidth. Thus, there is an optimum bandwidth that minimizes the altimetric error. Thirdly, the thesis studies the impact of sampling the GNSS signals with 1-level on the GNSS-R observables in terms of precision and of sensitivity to changes in the physical magnitudes. This work has importance because if 1-level samples were to be used, then the hardware requirements in terms of FPGA resources, transmission rate, hard drive write speed, and storage capacity will be reduced. Fourthly, the thesis discusses different architectures for real-time correlators in FPGAs compare to those in GPUs. Results show that GPUs can be used for real-time, with the advantage of being much more flexible and easier to program. Finally, the thesis investigates the cross-talk phenomena, or interference between GNSS satellites in the iGNSS-R technique. Results show that this kind of interference is not a problem in space-borne missions, but it does have an impact on airborne and ground-based ones. In such cases, antenna arrays with large directivity should be used. Returning to the instrument design objective, this thesis has two main goals. Firstly, to build the signal processing units inside the receivers and in the transmitter used to generate the calibration signal, and to develop the software to control both. Secondly, to process the data from different airborne fields campaigns using the GPU software mentioned above. The results have shown the feasibility of MIR for soil moisture estimation, sea altimetry, sea state, topography and water body/land transitions. |
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