Report of the panel on international programs

The panel recommends that NASA participate and take an active role in the continuous monitoring of existing regional networks, the realization of high resolution geopotential and topographic missions, the establishment of interconnection of the reference frames as defined by different space techniques, the development and implementation of automation for all ground-to-space observing systems, calibration and validation experiments for measuring techniques and data, the establishment of international space-based networks for real-time transmission of high density space data in standardized formats, tracking and support for non-NASA missions, and the extension of state-of-the art observing and analysis techniques to developing nations

Estimation of Azimuth Phase Undulations with Multisquint Processing in Airborne Interferometric SAR Images

This letter presents a technique to detect and correct phase errors appearing in interferometric airborne synthetic aperture radar (SAR) systems due to the lack of precision in the navigation system. The technique is based on a multisquint processing approach, i.e., by processing the same image pairs with different squint angles we can combine the information of different interferograms to obtain the desired phase correction. Airborne single-pass interferometric data from the Deutsches Zentrum für Luft- und Raumfahrt (DLR) Experimental airborne SAR is used to validate the metho

Measuring long-term and constant rate ground motion by satellite radar interferometry: Avcılar case

Radar interferometrisi (InSAR), birbirine çok yakın görüntüleme geometrileriyle elde edilmiş iki farklı radar görüntüsü arasında oluşan faz farkını hesaplayan bir tekniktir. Faz farkı, uydu platformunda bulunan radar ile yeryüzünde görüntülenen nokta arasındaki uzaklığa karşılık gelmektedir. Günümüzde InSAR, yüzey deformasyonunun ölçülmesinde etkili bir teknik olarak kabul edilmektedir. Diğer yandan, tekniğin uygulanabilirliği radar sinyalinin korelasyonu ve atmosferik etkilerle sınırlıdır. Bu çalışmada, uzun zamanda oluşan yüzey deformasyonunu ölçmek için, ERS-1 ve ERS-2 uydularından elde edilen radar görüntüleri kullanılarak bir strateji geliştirilmiştir. Yöntem, ham SAR verilerinin seçimi, SAR veri-işleme ve post-veri-işleme adımlarını içermektedir.  Çalışmada, Avrupa Uzay Ajansı’nın (ESA) 1992-2002 yılları arasında ERS uydularıyla elde ettiği radar görüntüleri kullanılmıştır. Radar görüntü çiftleri, çeşitli veri-seçimi kriterleriyle belirlenmiştir. Radar görüntülerindeki faz ölçmelerinin yoğunluğu, “permanent saçıcılar” (PS) tekniği kullanılarak azaltılmıştır. 1992 ve 1999 yılları arasındaki maksimum yerdeğiştirme hızı, Avcılar’ın batısında bir noktada -7 mm/yıl olarak belirlenmiştir. Birinci yazarın diğer çalışmalarında detaylı olarak belirtildiği üzere; Avcılar’da uzun zamandır sabit hızda oluşan yer hareketleri, bölgede var olduğu bilinen toprak kaymalarıyla ilişkilidir. Yerdeğiştime hızlarının dağılımı,  yağışlı mevsimde süreksiz olarak oluşan toprak kaymalarının, kayma ve oturma şeklinde bütün sene boyunca sürdüğünü göstermektedir. Anahtar Kelimeler: Uydu radar interferometrisi, yüzey deformasyonu, jeodezi, uzaktan algılama. Radar interferometry (InSAR) is a technique that calculates the phase difference between two radar images acquired by slightly different viewing geometries (Massonnet and Feigl, 1998; Hanssen, 2001; Madsen and Zebker, 1998; Burgmann et al., 2000; Rosen et al., 2000; Gens and van Genderen, 1996). The resultant interference pattern is called an “interferogram”. If certain conditions are met, the phase differences form spatially coherent fringes. Each fringe represents a difference of one cycle of the two-way travel time between the radar aboard the satellite and the target on the ground. Interpreted in units of distance, each fringe represents half the radar wavelength in change of distance, or 28 mm for C-band radars aboard ERS and ENVISAT satellites. While conventional InSAR has been proven to be a very effective technique to measure ground motion, its applicability is limited mainly by radar signal correlation and atmospheric effects. Therefore, to measure slow ground motion occurring over long times requires a challenging effort if conventional InSAR techniques are to be used. If one of the scatterers contributing to the pixel is much more stable than the others, then its contribution to the phase and amplitude measurements will dominate those from the other scatterers. If we can identify these pixels represented by a single strong scattarer, then we can simplify the process of interpreting the interferograms. These persistent scatterers (hence called “PS pixels”) are more reliable because they are less susceptible to all processes causing decorrelation. Accordingly, they have less noise then other pixels. Once the data set has been reduced in size by several orders of magnitude by selecting only the reliable PS pixels in the interferograms, the subsequent interpretation and analysis involving unwrapping and modeling are considerably simpler. Several approaches have been proposed for identifying PS pixels since 2000 (e.g. Hanssen and Usai, 1997; Ferretti et al., 2000, 2001; Colesanti et al., 2003a, 2003b; Lyons and Sandwell, 2003; Hooper et al., 2004; Hooper, 2006). In this study, we establish a radar data selection and processing flow for measuring slow ground motion occuring over long times. We combine different methodologies in raw radar data processing and post-processing. All the steps presented in the study are repeatable and applicable to ERS SAR data for measuring slow motion deformation. We use the entire radar data set of ERS-1 and ERS-2 satellites  for the data frame titled as Track 336 and Frame 2783 (T336/F2783). This frame covers all Istanbul metropolitan area and contains 48 epochs between 1992 and 2000. For the deformation analysis, we choose a data frame of 4x5 km2 that covers the Avcılar vicinity of Istanbul. We process the raw SAR data using DIAPASON software (Differential Interferometric Automated Process Applied to Survey of Nature) (version 4.1) developed at the French Space Agency (Massonnet et al., 1994; CNES, 1998; CNES, 2003a). The PS pixels persistent to phase decorrelation are selected through their “amplitude dispersion index” DA, as defined by Ferretti et al. (2000, 2001) and multi-coherence γ, as described by Colesanti (2003). We use “General Inversion for Phase Technique” (GIPhT) developed by Feigl and Thurber (2009) for modeling interferograms. GIPhT defines a misfit cost C between the model and the phase observations. By minimizing the cost C, this approach can solve simultaneously for both linear and non-linear parameters. Analysis of 14 image epochs between 1992 and 1999 has revealed downward ground motion around the Avcılar district of Istanbul. We have analyzed a set of 24 interferometric pairs with PS coverage of 7 PS/km2. The PS coverage corresponds to 1% of the image pixels. Three subsidence sources with a constant subsiding rate have been modeled by using a simple 4-parameter Mogi source (easting, northing, volume, depth). Also, a tropospheric parameter (vertical gradient) for each epoch has been included to the parameter set. The final model fits the phase data significantly better than the prior model based on F-test with 95 % confidence. We find a maximum displacement rate of -7 mm/yr at a point located at latitude 40.98ºN and longitude 28.71ºE. Akarvardar et al. (2007) and Akarvardar (2007) suggest that most of the downward ground motion occurs in the landslide areas. It seems likely that the soils once displaced after landslides have continued to slide and settle down with a constant rate between 1992 and 1999. Keywords: Satellite radar interferometry, ground motion, geodesy, remote sensing

Modes dégradés résultant de l'utilisation multi constellation du GNSS

Actuellement, on constate dans le domaine de la navigation, un besoin croissant de localisation par satellites. Apres une course a l'amelioration de la precision (maintenant proche de quelques centimetres grace a des techniques de lever d'ambiguite sur des mesures de phase), la releve du nouveau defi de l'amelioration de l'integrite du GNSS (GPS, Galileo) est a present engagee. L'integrite represente le degre de confiance que l'on peut placer dans l'exactitude des informations fournies par le systeme, ainsi que la capacite a avertir l'utilisateur d'un dysfonctionnement du GNSS dans un delai raisonnable. Le concept d'integrite du GNSS multi-constellation necessite une coordination au niveau de l'architecture des futurs recepteurs combines (GPS-Galileo). Le fonctionnement d'un tel recepteur dans le cas de passage du systeme multi-constellation en mode degrade est un probleme tres important pour l'integrite de navigation. Cette these se focalise sur les problemes lies a la navigation aeronautique multiconstellation et multi-systeme GNSS. En particulier, les conditions de fourniture de solution de navigation integre sont evaluees durant la phase d'approche APV I (avec guidage vertical). En disposant du GPS existant, du systeme Galileo et d'un systeme complementaire geostationnaire (SBAS), dont les satellites emettent sur des frequences aeronautiques en bande ARNS, la question fondamentale est comment tirer tous les benefices d'un tel systeme multi-constellation pour un recepteur embarque a bord d'un avion civil. En particulier, la question du maintien du niveau de performance durant cette phase de vol APV, en termes de precision, continuite, integrite et disponibilite, lorsque l'une des composantes du systeme est degradee ou perdu, doit etre resolue. L'objectif de ce travail de these est donc d'etudier la capacite d'un recepteur combine avionique d'effectuer la tache de reconfiguration de l'algorithme de traitement apres l'apparition de pannes ou d'interferences dans une partie du systeme GNSS multiconstellation et d'emettre un signal d'alarme dans le cas ou les performances de la partie du systeme non contaminee ne sont pas suffisantes pour continuer l'operation en cours en respectant les exigences de l'aviation civile. Egalement, l'objectif de ce travail est d'etudier les methodes associees a l'execution de cette reconfiguration pour garantir l'utilisation de la partie du systeme GNSS multi-constellation non contaminee dans les meilleures conditions. Cette etude a donc un interet pour les constructeurs des futurs recepteurs avioniques multiconstellation. ABSTRACT : The International Civil Aviation Organization (ICAO) has defined the concept of Global Navigation Satellite System (GNSS), which corresponds to the set of systems allowing to perform satellite-based navigation while fulfilling ICAO requirements. The US Global Positioning Sysem (GPS) is a satellite-based navigation system which constitutes one of the components of the GNSS. Currently, this system broadcasts a civil signal, called L1 C/A, within an Aeronautical Radio Navigation Services (ARNS) band. The GPS is being modernized and will broadcast two new civil signals: L2C (not in an ARNS band) and L5 in another ARNS band. Galileo is the European counterpart of GPS. It will broadcast three signals in an ARNS band: Galileo E1 OS (Open Service) will be transmitted in the GPS L1 frequency band and Galileo E5a and E5b will be broadcasted in the same 960-1215 MHz ARNS band than that of GPS L5. GPS L5 and Galileo E1, E5a, E5b components are expected to provide operational benefits for civil aviation use. However, civil aviation requirements are very stringent and up to now, the bare systems alone cannot be used as a means of navigation. For instance, the GPS standalone does not implement sufficient integrity monitoring. Therefore, in order to ensure the levels of performance required by civil aviation in terms of accuracy, integrity, continuity of service and availability, ICAO standards define different systems/algorithms to augment the basic constellations. GPS, Galileo and the augmentation systems could be combined to comply with the ICAO requirements and complete the lack of GPS or Galileo standalone performance. In order to take benefits of new GNSS signals, and to provide the service level required by the ICAO, the architecture of future combined GNSS receivers must be standardized. The European Organization for Civil Aviation Equipment (EUROCAE) Working Group 62, which is in charge of Galileo standardization for civil aviation in Europe, proposes new combined receivers architectures, in coordination with the Radio Technical Commission for Aeronautics (RTCA). The main objective of this thesis is to contribute to the efforts made by the WG 62 by providing inputs necessary to build future receivers architecture to take benefits of GPS, Galileo and augmentation systems. In this report, we propose some key elements of the combined receivers' architecture to comply with approach phases of flight requirements. In case of perturbation preventing one of the needed GNSS components to meet a phase of flight required performance, it is necessary to be able to switch to another available component in order to try to maintain if possible the level of performance in terms of continuity, integrity, availability and accuracy. That is why future combined receivers must be capable of detecting the impact of perturbations that may lead to the loss of one GNSS component, in order to be able to initiate a switch. These perturbations are mainly atmospheric disturbances, interferences and multipath. In this thesis we focus on the particular cases of interferences and ionosphere perturbations. The interferences are among the most feared events in civil aviation use of GNSS. Detection, estimation and removal of the effect of interference on GNSS signals remain open issues and may affect pseudorange measurements accuracy, as well as integrity, continuity and availability of these measurements. In literature, many different interference detection algorithms have been proposed, at the receiver antenna level, at the front-end level. Detection within tracking loops is not widely studied to our knowledge. That is why, in this thesis, we address the problem of interference detection at the correlators outputs. The particular case of CW interferences detection on the GPS L1 C/A and Galileo E1 OS signals processing is proposed. Nominal dual frequency measurements provide a good estimation of ionospheric delay. In addition, the combination of GPS or GALILEO navigation signals processing at the receiver level is expected to provide important improvements for civil aviation. It could, potentially with augmentations, provide better accuracy and availability of ionospheric correction measurements. Indeed, GPS users will be able to combine GPS L1 and L5 frequencies, and future GALILEO E1 and E5 signals will bring their contribution. However, if affected by a Radio Frequency Interference, a receiver can lose one or more frequencies leading to the use of only one frequency to estimate the ionospheric code delay. Therefore, it is felt by the authors as an important task to investigate techniques aimed at sustaining multi-frequency performance when a multi constellation receiver installed in an aircraft is suddenly affected by radiofrequency interference, during critical phases of flight. This problem is identified for instance in [NATS, 2003]. Consequently, in this thesis, we investigate techniques to maintain dual frequency performances when a frequency is lost (L1 C/A or E1 OS for instance) after an interference occurrence

Earth resources: A continuing bibliography with indexes (issue 52)

This bibliography lists 454 reports, articles, and other documents introduced into the NASA scientific and technical information system between October 1 and December 31, 1986. Emphasis is placed on the use of remote sensing and geophysical instrumentation in spacecraft and aircraft to survey and inventory natural resources and urban areas. Subject matter is grouped according to agriculture and forestry, environmental changes and cultural resources, geodesy and cartography, geology and mineral resources, hydrology and water management, data processing and distribution systems, instrumentation and sensors, and economic analysis

Investigations carried out under the Director's Discretionary Fund

This annual report comprises a set of summaries, describing task objectives, progress and results or accomplishments, future outlook, and financial status for each director's discretionary fund (DDF) task that was active during fiscal year 1984. Publications and conference presentations related to the work are listed. The individual reports are categorized as interim or final according to whether the task efforts are ongoing or completed. A partial list of new tasks to be initiated with fiscal year 1985 funds and a glossary of abbreviations and acronyms, used by the task authors in their summaries are included. The table of contents lists the DDF reports in sequence by their task number, which is derived from the 13-digit code assigned to account for the fund awarded to the task project

Solid Earth science in the 1990s. Volume 3: Measurement techniques and technology

Reports are contained from the NASA Workshop on Solid Earth Science in the 1990s. The techniques and technologies needed to address the program objectives are discussed. The Measurement Technique and Technology Panel identified (1) candidate measurement systems for each of the measurements required for the Solid Earth Science Program that would fall under the NASA purview; (2) the capabilities and limitations of each technique; and (3) the developments necessary for each technique to meet the science panel requirements. In nearly all cases, current technology or a development path with existing technology was identified as capable of meeting the requirements of the science panels. These technologies and development paths are discussed

The applications of satellites to communications, navigation and surveillance for aircraft operating over the contiguous United States. Volume 1 - Technical report

Satellite applications to aircraft communications, navigation, and surveillance over US including synthesized satellite network and aircraft equipment for air traffic contro