Beyond the spatio-temporal limits of atmospheric radars: inverse problem techniques and MIMO systems

The Earth’s upper atmosphere (UA) is a highly dynamic region dominated by atmospheric waves and stratified turbulence covering a wide range of spatio-temporal scales. A comprehensive study of the UA requires measurements over a broad range of frequencies and spatial wavelengths, which are prohibitively costly. To improve the understanding of the UA, an investment in efficient and large observational infrastructures is required. This work investigates remote sensing techniques based on MIMO and inverse problems techniques to improve the capabilities of current atmospheric radars

A Study in GPS-Denied Navigation Using Synthetic Aperture Radar

In modern navigation systems, GPS is vital to accurately piloting a vehicle. This is especially true in autonomous vehicles, such as UAVs, which have no pilot. Unfortunately, GPS signals can be easily jammed or spoofed. For example, canyons and urban cities create an environment where the sky is obstructed and make GPS signals unreliable. Additionally, hostile individuals can transmit personal signals intended to block or spoof GPS signals. In these situations, it is important to find a means of navigation that doesn’t rely on GPS. Navigating without GPS means that other types of sensors or instruments must be used to replace the information lost from GPS. Some examples of additional sensors include cameras, altimeters, magnetometers, and radar. The work presented in this thesis shows how radar can be used to navigate without GPS. Specifically, synthetic aperture radar (SAR) is used, which is a method of processing radar data to form images of a landscape similar to images captured using a camera. SAR presents its own unique set of benefits and challenges. One major benefit of SAR is that it can produce images of an area even at night or through cloud cover. Additionally, SAR can image a wide swath of land at an angle that would be difficult for a camera to achieve. However, SAR is more computationally complex than other imaging sensors. Image quality is also highly dependent on the quality of navigation information available. In general, SAR requires that good navigation data be had in order to form SAR images. The research here explores the reverse problem where SAR images are formed without good navigation data and then good navigation data is inferred from the images. This thesis performs feasibility studies and real data implementations that show how SAR can be used in navigation without the presence of GPS. Derivations and background materials are provided. Validation methods and additional discussions are provided on the results of each portion of research

Innovative Adaptive Techniques for Multi Channel Spaceborne SAR Systems

Synthetic Aperture Radar (SAR) is a well-known technology which allows to coherently combine multiple returns from (typically) ground-based targets from a moving radar mounted either on an airborne or on a space-borne vehicle. The relative motion between the targets on ground and the platform causes a Doppler effect, which is exploited to discriminate along-track positions of targets themselves. In addition, as most of conventional radar, a pulsed wide-band waveform is transmitted periodically, thus allowing even a radar discrimination capability in the range direction (i.e. in distance). For side-looking acquisition geometries, the along-track and the range directions are almost orthogonal, so that the two dimensional target discrimination capabiliy results in the possibility to produce images of the illuminated area on ground. A side-looking geometry consists in the radar antenna to be, either mechanically or electronically, oriented perpendicular to the observed area. Nowadays technology allows discrimination capability (also referred to as resolution) in both alongtrack and range directions in the order of few tenths of centimeters. Since the SAR is a microwave active sensor, this technology assure the possibility to produce images of the terrain independently of the sunlight illumination and/or weather conditions. This makes the SAR a very useful instrument for monitoring and mapping both the natural and the artificial activities over the Earth’s surface. Among all the limitations of a single-channel SAR system, this work focuses over some of them which are briefly listed below: a) the performance achievable in terms of resolution are usually paid in terms of system complexity, dimension, mass and cost; b) since the SAR is a coherent active sensor, it is vulnerable to both intentionally and unintentionally radio-frequency interferences which might limit normal system operability; c) since the Doppler effect it is used to discriminate targets (assumed to be stationary) on the ground, this causes an intrinsic ambiguity in the interpretation of backscattered returns from moving targets. These drawbacks can be easily overcome by resorting to a Multi-cannel SAR (M-SAR) system

Préparation à l'utilisation des observations de l'imageur d'éclairs de Météosat troisième génération pour la prévision numérique à courte échéance

En guise d'analyse initiale, une intercomparaison d'observations d'éclairs au-dessus de la Corse issues du détecteur Lightning Imaging Sensor de la Station Spatiale Internationale (ISS-LIS), du réseau de Météorage de basse fréquence (LF) et du réseau Lightning Mapping Array (LMA) SAETTA révèle que des enregistrements coïncidents des trois systèmes de localisation des éclairs peuvent être identifiés. Les éclairs de grande extension et de longue durée sont plus susceptibles d'être simultanément détectés par ISS-LIS et Météorage que les éclairs de petite extension et de courte durée. En utilisant les informations fournies par SAETTA, on constate que l'efficacité de détection des éclairs de l'instrument spatial ISS-LIS se dégrade pour les éclairs détectés par Météorage qui ne s'étendent pas sur plus de 7 km d'altitude. Cette méthodologie d'intercomparaison est aussi appliquée pour analyser les enregistrements du capteur spatial ISS-LIS par rapport aux observations du réseau National Lightning Detection Network (NLDN) sur le sud-est des États-Unis. Dans l'ensemble, les caractéristiques des éclairs analysées dans les deux régions ne sont pas seulement similaires quand elles sont comparées aux enregistrements du détecteur spatial ISS-LIS, mais aussi lorsque l'on compare leurs statistiques telles que décrites indépendamment par Météorage et NLDN. Il est conclu que Météorage et NLDN détectent et localisent les éclairs de la même manière. Avec l'avènement du détecteur spatial géostationnaire (GEO) Geostationary Lightning Mapper (GLM), les observations coïncidentes de ce même détecteur GLM avec des observations du réseau terrestre NLDN sont analysées en détail pour construire un algorithme complexe générant des données synthétiques géostationnaires d'éclairs à partir des données du réseau NLDN. Ce générateur de données synthétiques d'éclairs utilise d'abord différentes caractéristiques des éclairs déduites des observations NLDN et GLM pour entraîner des modèles d'apprentissage automatique, et crée ensuite les différents pixels lumineux constituant chaque éclair synthétique à partir des caractéristiques de ce même éclair. Enfin, ce générateur est appliqué aux enregistrements du réseau français Météorage afin de simuler des observations synthétiques de l'imageur Lightning Imager (LI) de la mission Meteosat Troisième Génération (MTG) au-dessus de la France. Finalement, la densité d'étendue des éclairs (FED) est calculée à partir de ces données synthétiques MTG-LI. La FED sert ensuite de source de données pour un nouveau schéma d'assimilation de données d'éclairs (LDA) dans le modèle opérationnel français AROME-France. Ici, une restitution bayésienne à 1 dimension (1DBay) inverse la densité FED et fournit des profils d'humidité relative. La méthode 1DBay s'avère efficace pour supprimer la convection parasite et pour favoriser la convection dans les régions à FED positive. En dernier lieu, les profils d'humidité relative restitués sont assimilés à l'aide du système variationnel 3D (3DVar) du modèle AROME-France. Malgré les résultats prometteurs de la méthode 1DBay, l'analyse AROME-France contredit les profils d'humidité relative restitués dans la mesure où l'humidité est augmentée dans certaines régions où les profils d'humidité relative restitués suggèrent une réduction de l'humidité de l'ébauche.As an initial analysis, an intercomparison of lightning observations over Corsica from the Lightning Imaging Sensor on the International Space Station (ISS-LIS), the Low Frequency (LF) Meteorage network, and the SAETTA Lightning Mapping Array (LMA) reveals that coincident flashes of all three lightning locating systems can be identified. Large and long-duration flashes are more likely detected by both ISS-LIS and Meteorage than small and short-duration flashes. Using the information provided by SAETTA, it is found that the flash detection efficiency of ISS-LIS degrades for flashes detected by Meteorage that do not extend over 7 km of altitude. This intercomparison methodology is further applied to analyze records of ISS-LIS relative to National Lightning Detection Network (NLDN) observations over the southeastern USA. Overall, the flash characteristics analyzed in both French and US regions are not only similar from ISS-LIS records, but also when comparing their statistics as depicted by Meteorage and NLDN. It is concluded that Meteorage and NLDN detect and locate lightning similarly. With the advent of the Geostationary Lightning Mapper (GLM) concurrent geostationary (GEO) GLM and ground-based NLDN lightning observations are analyzed in detail to develop a complex algorithm to generate GEO lightning pseudo-observations from NLDN records. The so-called GEO lightning pseudo-observation generator first relates NLDN and GLM flash characteristics to train machine learning models, and secondly creates pseudo-GEO events from the simulated GEO flash characteristics. Finally, this generator is applied to simulate synthetic Meteosat Third Generation (MTG) Lightning Imager (LI) observations over France using Meteorage records as input. Eventually, Flash Extent Density (FED) is inferred from that pseudo MTG-LI data. Pseudo MTG-LI FED serves as data source for a new lightning data assimilation (LDA) scheme in the French operational model AROME-France. Here, a 1-dimensional Bayesian (1DBay) retrieval inverts the FED observations and provides relative humidity (RH) profiles. The 1DBay proves to suppress spurious convection and promote convection in regions with positive FED. As a last step, retrieved RH profiles are assimilated using the 3D variational (3DVar) system of AROME-France. Despite promising results of the 1DBay, the AROME-France analysis contradicts the retrieved RH profiles in that humidity is increased in some regions where the retrieved RH profiles suggest a reduction of the background humidity

Radar Technology

In this book “Radar Technology”, the chapters are divided into four main topic areas: Topic area 1: “Radar Systems” consists of chapters which treat whole radar systems, environment and target functional chain. Topic area 2: “Radar Applications” shows various applications of radar systems, including meteorological radars, ground penetrating radars and glaciology. Topic area 3: “Radar Functional Chain and Signal Processing” describes several aspects of the radar signal processing. From parameter extraction, target detection over tracking and classification technologies. Topic area 4: “Radar Subsystems and Components” consists of design technology of radar subsystem components like antenna design or waveform design

Innovative Adaptive Techniques for Multi Channel Spaceborne SAR Systems

Synthetic Aperture Radar (SAR) is a well-known technology which allows to coherently combine multiple returns from (typically) ground-based targets from a moving radar mounted either on an airborne or on a space-borne vehicle. The relative motion between the targets on ground and the platform causes a Doppler effect, which is exploited to discriminate along-track positions of targets themselves. In addition, as most of conventional radar, a pulsed wide-band waveform is transmitted periodically, thus allowing even a radar discrimination capability in the range direction (i.e. in distance). For side-looking acquisition geometries, the along-track and the range directions are almost orthogonal, so that the two dimensional target discrimination capabiliy results in the possibility to produce images of the illuminated area on ground. A side-looking geometry consists in the radar antenna to be, either mechanically or electronically, oriented perpendicular to the observed area. Nowadays technology allows discrimination capability (also referred to as resolution) in both alongtrack and range directions in the order of few tenths of centimeters. Since the SAR is a microwave active sensor, this technology assure the possibility to produce images of the terrain independently of the sunlight illumination and/or weather conditions. This makes the SAR a very useful instrument for monitoring and mapping both the natural and the artificial activities over the Earth’s surface. Among all the limitations of a single-channel SAR system, this work focuses over some of them which are briefly listed below: a) the performance achievable in terms of resolution are usually paid in terms of system complexity, dimension, mass and cost; b) since the SAR is a coherent active sensor, it is vulnerable to both intentionally and unintentionally radio-frequency interferences which might limit normal system operability; c) since the Doppler effect it is used to discriminate targets (assumed to be stationary) on the ground, this causes an intrinsic ambiguity in the interpretation of backscattered returns from moving targets. These drawbacks can be easily overcome by resorting to a Multi-cannel SAR (M-SAR) system

3D space intersection features extraction from Synthetic Aperture Radar images

The main purpose of this Thesis is to develop new theoretical models in order to extend the capabilities of SAR images space intersection techniques to generate three dimensional information. Furthermore, the study aims at acquiring new knowledge on SAR image interpretation through the three dimensional comprehension of the scene. The proposed methodologies allow to extend the known radargrammetric applications to vector data generation, exploiting SAR images acquired with every possible geometries. The considered geometries are points, circles, cylinders and lines. The study assesses the estimation accuracy of the features in terms of absolute and relative position and dimensions, analyzing the nowadays operational SAR sensors with a special focus on the national COSMO-SkyMed system. The proposed approach is original as it does not require the direct matching between homologous points of different images, which is a necessary step for the classical radargrammetric techniques; points belonging to the same feature, circular or linear, recognized in different images, are matched through specific models in order to estimate the dimensions and the location of the feature itself. This approach is robust with respect to the variation of the viewing angle of the input images and allows to better exploit archive data, acquired with diverse viewing geometries. The obtained results confirm the validity of the proposed theoretical approach and enable important applicative developments, especially in the Defence domain: (i) introducing original three dimensional measurement tools to support visual image interpretation; (ii) performing an advanced modelling of building counting only on SAR images; (iii) exploiting SAR images as a source for geospatial information and data; (iv) producing geospatial reference information, such as Ground Control Point, without any need for survey on the ground

Scientific applications of radio and radar tracking in the space program Conference proceedings

Radar and radio tracking applications in space progra

Advanced Signal Processing For Multi-Mission Airborne Radar

With the technological advancement of the 21st century, functions of different radars are being merged. A multi-functional system brings the technology of remote sensing to a wide array of applications while at the same time reduces costs of implementation and operation. Ground-based multi-mission radars have been studied in the past. The airborne counterpart deserves a through study with additional and stringent requirements of cost, size, weight, and power.In this dissertation, multi-mission functions in an airborne radar is performed using modular, software-based architecture. The software-based solution is chosen instead of proposing new hardware, primarily because evaluation, validation, and certification of new hardware is onerous and time consuming. The system implementations are validated using simulations as well as field measurements. The simulations are carried out using Mathworks® Phased Array System Toolbox. The field measurements are performed using an enhanced commercial airborne radar system called Polarimetric Airborne Radar Operating at X-band Version 1 (PARADOX1), which is an X-band, vertically polarized, solid state, pulsed radar.The shortcomings of PARADOX1 originate from small aperture size and low power. Various signal processing algorithms are developed and applied to PARADOX1 data to enhance the data quality. Super-resolution algorithms in range, angle, and Doppler domains, for example, have proven to effectively enhance the spatial resolution. An end-to-end study of single-polarized weather measurements is performed using PARADOX1 measurements. The results are compared with well established ground-based radars. The similarities, differences as well as limitations (of such comparisons) are discussed. Sense and Avoid (SAA) tracking is considered as a core functionality and presented in the context of safe integration of Unmanned Aerial Vehicles (UAV) in national airspace. A "nearly" constant acceleration motion model is used in conjunction with Kalman Filter and Joint Probabilistic Data Association (JPDA) to perform tracking operations. The basic SAA tracking function is validated through simulations as well as field measurements.The field-validations show that a modular, software-based enhancement to an existing radar system is a viable solution in realizing multi-mission functionalities in an airborne radar. The SAA tracking is validated in ground-based tests using an x86 based PC with a generic Linux operating system. The weather measurements from PARADOX1 and the subsequent data quality enhancements show that PARADOX1 data products are comparable to those of existing ground based radars

Navigation and guidance requirements for commercial VTOL operations

The NASA Langley Research Center (LaRC) has undertaken a research program to develop the navigation, guidance, control, and flight management technology base needed by Government and industry in establishing systems design concepts and operating procedures for VTOL short-haul transportation systems in the 1980s time period. The VALT (VTOL Automatic Landing Technology) Program encompasses the investigation of operating systems and piloting techniques associated with VTOL operations under all-weather conditions from downtown vertiports; the definition of terminal air traffic and airspace requirements; and the development of avionics including navigation, guidance, controls, and displays for automated takeoff, cruise, and landing operations. The program includes requirements analyses, design studies, systems development, ground simulation, and flight validation efforts