In-Orbit SAR Performance of TerraSAR-X

TerraSAR-X is the first German Radar satellite for scientific and commercial applications. The project is a public-private partnership between DLR and EADS Astrium GmbH. TerraSAR-X consists of a high resolution Synthetic Aperture Radar at X-Band. The radar antenna is based on active phased array technology that allows the control of many different instrument parameters and operational modes (Stripmap, ScanSAR and Spotlight) with various polarizations. Following the TerraSAR-X launch, scheduled for February 2007, it is planned a six month Commissioning Phase covering the characterization and verification of the SAR mission. Within this phase, the Overall SAR System Performance (OSSP) takes care of the correct working and interaction of all SAR system elements essential for obtaining an optimum SAR Performance. The paper covers the first in-orbit characterization and verification results of the SAR system performance for TerraSAR-X operational and experimental modes. This characterization is divided into four phases: Initial Characterization, Scene Characterization –both mostly based on basic and experimental products-, and Verification of TS-X Instrument Command Generation. The different optimization strategies and performance trade-offs are discussed and presented in the paper, including very first TerraSAR-X images. The result of the real SAR data analysis determines the final system baseline and thus the final image quality, e.g. Temperature compensation, Total Zero Doppler Steering, Up/down chirp toggling, transmitted bandwidth, timing interferences, etc. The first section of the paper introduces the activities carried out during the Commissioning Phase for the TerraSAR-X SAR system performance characterization/verification. In the second section, the strategies for the performance optimization and characterization are presented. Finally, the in-orbit SAR performance results are given in section three

Bistatic Experiment Using TerraSAR-X and DLR’s new F-SAR System

A bistatic X-band experiment was successfully performed early November 2007. TerraSAR-X was used as transmitter and DLR’s new airborne radar system F-SAR, which was programmed to acquire data in a quasi-continuous mode to avoid echo window synchronization issues, was used as bistatic receiver. Precise phase and time referencing between both systems, which is essential for obtaining high resolution SAR images, was derived during the bistatic processing. Hardware setup and performance analyses of the bistatic configuration are pre-sented together with first processing results that verify the predicted synchronization and imaging performance

DELTA-K WIDEBAND SAR INTERFEROMETRY FOR DEM GENERATION AND PERSISTENT SCATTERERS USING TERRASAR-X

ABSTRACT Wideband SAR systems such as TerraSAR-X allow estimation of the absolute interferometric phase without resorting to error prone phase unwrapping. This is achieved through the delta-k technique that exploits frequency diversity within the range bandwidth to simulate a SAR system with a much longer carrier wavelength. This benefits all interferometric applications including DEM generation and land surface motion determination. Here we present the results of an ESA study (21318/07/NL/HE) into using delta-k absolute phase estimation for DEM generation and PSI (Persistent Scatterer Interferometry). Using TerraSAR-X data, examples from a delta-k DEM generation system are shown which avoid the errors induced by conventional phase unwrapping. For PSI, the possibilities of absolute phase estimation for a single PS are explored in theory and examples where wideband estimation is compared to conventional PSI processing for a stack of acquisitions over Paris

An incoherent feedforward loop interprets NFκB/RelA dynamics to determine TNF-induced necroptosis decisions

Balancing cell death is essential to maintain healthy tissue homeostasis and prevent disease. Tumor necrosis factor (TNF) not only activates nuclear factor κB (NFκB), which coordinates the cellular response to inflammation, but may also trigger necroptosis, a pro-inflammatory form of cell death. Whether TNF-induced NFκB affects the fate decision to undergo TNF-induced necroptosis is unclear. Live-cell microscopy and model-aided analysis of death kinetics identified a molecular circuit that interprets TNF-induced NFκB/RelA dynamics to control necroptosis decisions. Inducible expression of TNFAIP3/A20 forms an incoherent feedforward loop to interfere with the RIPK3-containing necrosome complex and protect a fraction of cells from transient, but not long-term TNF exposure. Furthermore, dysregulated NFκB dynamics often associated with disease diminish TNF-induced necroptosis. Our results suggest that TNF's dual roles in either coordinating cellular responses to inflammation, or further amplifying inflammation are determined by a dynamic NFκB-A20-RIPK3 circuit, that could be targeted to treat inflammation and cancer

Evaluating the Impact of Intravitreal Aflibercept on Diabetic Retinopathy Progression in the VIVID-DME and VISTA-DME Studies

Purpose To evaluate the impact of intravitreal aflibercept (EYLEA, Regeneron Pharmaceuticals, Tarrytown, NY) versus laser on progression of diabetic retinopathy (DR) severity in Intravitreal Aflibercept Injection in Vision Impairment due to DME (VIVID-DME) and Study of Intravitreal Aflibercept Injection in Patients with Diabetic Macular Edema (VISTA-DME). Design Secondary and exploratory analyses of 2 phase 3, randomized, controlled studies. Participants All patients with a baseline Diabetic Retinopathy Severity Scale (DRSS) score based on fundus photograph (full analysis), patients who progressed to proliferative DR (PDR) (safety analysis) in VIVID-DME (n = 403) and VISTA-DME (n = 459), or both. Methods We randomized patients with diabetic macular edema (DME) to intravitreal aflibercept 2 mg every 4 weeks (2q4), intravitreal aflibercept 2 mg every 8 weeks after 5 initial monthly doses (2q8), or macular laser photocoagulation at baseline and sham injections at every visit. Main Outcome Measures Proportions of patients with 2-step or more and 3-step or more improvements from baseline in DRSS score, who progressed to PDR, and who underwent panretinal photocoagulation (PRP). Results Among patients with an assessable baseline DRSS score, most showed moderately severe or severe nonproliferative DR. The proportions of patients treated with 2q4, 2q8, and laser with a 2-step or more improvement in DRSS score at week 100 were 29.3%, 32.6%, and 8.2%, respectively, in VIVID-DME and 37.0%, 37.1%, and 15.6%, respectively, in VISTA-DME; the proportions with a 3-step or more improvement in DRSS score were 7.3%, 2.3%, and 0%, respectively, and 22.7%, 19.9%, and 5.2%, respectively. Fewer patients in the 2q4 and 2q8 groups versus the laser group progressed to PDR at week 100 in VISTA-DME (1.5% and 2.2% vs. 5.3%) and VIVID-DME (3.2% and 2.0% vs. 12.3%). The proportions of patients who underwent PRP were 2.9%, 0.7%, and 4.5%, respectively, in VIVID-DME and 1.9%, 0.7%, and 5.2%, respectively, in VISTA-DME. The most frequent serious ocular adverse event at week 100 was cataract (pooled intravitreal aflibercept, 1.7% of patients; laser, 3.5% of patients). Conclusions These analyses demonstrate the benefit of intravitreal aflibercept over laser with respect to DR progression, suggesting a benefit on DME, and on underlying DR

Performance Prediction and Verification for Bistatic SAR Synchronization Link

Bistatic SAR systems have a high potential for scientific, commercial and security applications. One of the benefits is the possibility to generate highly accurate digital elevation models using bistatic interferometry. Examples for proposed bi- and multi-static satellite missions with interferometric capabilities are TanDEM-X and Cartwheel. Both are based on radar instruments placed on different spacecrafts, which gives rise to several technical challenges for the system realization. A factor which may severely degrade the performance of a bistatic SAR is the phase instability of the two oscillators involved. Investigations have shown, that, unless highly stable oscillators are used, the oscillators phase noise has to be compensated; this is possible through the processed SAR data in combination with ground control points, or by establishing a synchronization link to directly exchange signals providing information on the oscillator phase noise. The later method is based on recording the received demodulated phases, which are then used to derive a compensation signal to correct the SAR data. The paper describes a possible configuration for the synchronization link, sharing hardware components with the SAR instrument. Such a system is currently intended for the TanDEM-X mission. The resulting restrictions on the synchronization scheme, timing, and accuracy are investigated. The statistical properties of the compensation signal are used to derive a figure-of-merit for synchronization performance. The focus is on the influence of the synchronization link RF hardware on the quality of the derived compensation signal. Therefore a hardware setup is realized and characterized to obtain realistic data. Further, a simulation tool is implemented to predict the performance. The simulation tool is based on a synchronization link hardware model which can use measurement data as an input. Finally, the complete synchronization process is verified by measurements using the test hardware

TerraSAR-X INSTRUMENT IN-ORBIT VERIFICATION PLAN

This instrument In-Orbit Verification (IOV) plan defines the verification programme for the SAR system related parts of the TerraSAR-X spacecraft during the Launch and Early Orbit Phase (LEOP) and the In-Orbit Commissioning (IOC) phase of the TerraSAR-X mission