Algorithm to changing bistatic imaging geometric model for TH-2 satellite

Imaging geometric model of master and slave satellite directly affects many steps in InSAR data processsing, such as complex image rough registration, flat plain effect removing, InSAR location, baseline calibration, block adjustment and ortho-rectification. In order to keep unified algorithm in imageing, both master and slave satellite of TH-2 use bistatic imaging geometric model. For complex image rough registration, flat plain effect removing and InSAR location step, bistatic imaging geometric model just increase algorithm complexity, but for baseline calibration, it brings new chanlleges. On one hand, most current baseline calibration algorithms are based on monostatic imaging geometric model and can not be used in TH-2; on the other hand, pair position combines to form four baselines, and four baselines exist correlation in calibration, which leads to difficulty for baseline calibration. In order to keep accuracy of baseline calibration, the paper presents algorithm to chang bistatic geometric model into monostatic model and anlyses the transformation accuracy for slave satellite. It's proved that the algorithm has high accuracy and the brought error can be ignored by theoretical analysis and test

Key technologies of TH-2 satellite system

The TH-2 satellite system is the first microwave surveying satellite system based on interferometric synthetic aperture radar (InSAR) technology and the first short-range formation satellite system in China. It is composed of two equal satellites, and the satellites formation in different orbits and the bistatic radar transceiver mode are adopted. By using satellite formations to form the baseline needed for interference, it can measure the global digital surface models by scale of 1∶50 000 in a short time and acquire radar orthophotos at the same time. This paper gives a detailed introduction of the InSAR measurement principle and the technical system of TH-2 is also expounded carefully. To ensure the performance of system and the accuracy of product, several key techniques such as satellite formation, cooperative mode of two satellites, high-precision internal calibration, baseline determination, high-precision baseline measurement, high-precision baseline calibration, imaging of high phase fidelity and absolute ambiguity number calculation using dual-frequency need to be solved. These key technologies are analyzed in this paper, and the solutions are proposed. During the development of the TH-2 satellite system, simulation data and semi-physical simulation test were used to verify the feasibility of the main key technology solutions. After the satellites were launched, the on orbit test showed that the system was operating in good condition and the main performance indicators were better than the designed indicators, which further verified the feasibility of the key technology solutions and the correctness of these methods

Comparison and analysis of two baseline calibration models for TH-2 satellite

The two equivalent satellites in the TH-2 satellite system formed a flying-around formation in early July 2019, and began to obtain global radar interference data using the one-transmit and double-receiving system. The precise interference baseline is to realize the production of high-precision surveying and mapping products. This article gives the definition of the baseline in the antenna phase center (APC) coordinate system of the main radar. It introduces the single-scene data baseline calibration model based on the slave radar range modification equation and doppler equation under the one-transmit and double-receiving system, and a joint near-far beam positions calibration model of obtaining parallel and effective baseline errors by steps. According to the principle of baseline error intersection, a control points selection strategy is given, that is, the strategy of selecting control points in the near and far sub strips. The 17 times Xinjiang calibration field data acquired by TH-2 was used to carry out single-scene data and near-far beam positions joint baseline calibration experiments, and the ground positioning precision analysis of the two baseline calibration models after calibration was carried out. The experiments show that the average horizontal baseline error is -2.74 mm, and the average vertical baseline error is -5.49 mm calibrated by the single-scene data model. The average horizontal baseline error is -1.95 mm, and the average vertical baseline error is -5.84 mm calibrated by the near-far beam positions joint model. The ground positioning precision of the system after the near-far beam positions joint baseline calibration is higher than that of the single-scene data baseline calibration

Inclination Angle Error Compensation Algorithm of MIMO Downward-looking Array SAR

Combined with the real POS data form, elements of exterior orientation of traditional optical photogrammetry were introduced, and inclination angle error compensation methods of MIMO downward-looking array SAR were designed.The beam-independent phase error was compensated in the three-dimensional spatial domain firstly.Then the compensated echo data was transformed into the two-dimensional wavenumber domain in along-track and cross-track directions, and was equally divided into M and N segments.The MN subblocks were zeroed and extended to the original size, transformed into the two-dimensional spatial domain in along-track and cross-track directions and wavenumber domain in range direction, and the beam-dependent phase error was compensated.Then, the subblock echo data were transformed into three-dimensional spatial domain, and added directly to the final data.Finally, the correct 3D imaging results could be obtained by 3D RD imaging algorithm.The effectiveness of the proposed method was verified by simulation experiments

TH-2 satellite engineering design and implementation

The TH-2 satellite system is China's first microwave surveying satellite system based on interferometric synthetic aperture radar technology, and is also China's first short-range formation satellite system. It is the second microwave interferometric surveying satellite system after the German's TanDEM-X system in the world. A method to solve the problem of absolute ambiguity in the interference phase by designing dual-frequency imaging is proposed for the first time in the world, which completely got rid of the dependence on ground control data. The system works in the X band, with the resolution of 3 m and a solar synchronous orbit of 500 km. It is composed of two equal satellites. It adopts a technical system of satellite formation in different orbits and a bistatic radar transceiver mode. It can measure the global digital surface models and acquire radar orthophotos in a short time. In this paper, through the selection of the interference baseline system, satellite formation configuration and radar transceiver mode, the technical system of TH-2 satellite is proposed. The engineering design is carried out from three aspects:system mission, main performance and composition. The implementation of the project is expounded from the three stages of the overall demonstration, the key technical research and verification, and project development. Finally, the on-orbit test and verification of the satellite system is introduced. Test results show that all indicators have reached the requirements of engineering design, products' precision is equivalent to TanDEM -X system and can meet the 1:50 000 scale mapping accuracy. These verify the TH-2 satellite' engineering design ideas correct and the method of project implementation reasonable and feasible

Layover and shadow regions detection based on superpixel segmentation and multi-information fusion

In InSAR signal processing, the continuity of InSAR phase maps is seriously destroyed by layover and shadow regions which results in errors in elevation inversion. In this paper, a multi-information fusion-based superpiexl detection algorithm is proposed to make up for the shortcomings of traditional pixel-by-pixel detection methods based on amplitude and coherence coefficient threshold detection, constant false alarm(CFAR) detection and local frequency detection. Due to the lack of digital elevation model of scene, the accuracy verification of the proposed algorithm in practical applications become impossible. Thus, a frequency domain echo simulation technique is proposed. The proposed algorithm is verified based on an advanced integral equation approximation model(AIEM) for simulating SAR echo data. Simulation data and TH-2 data experiments show that the algorithm can distinguish more than 98% of layover and shadow regions in SAR images. Finally, the DEM products precision and the operation efficiency of phase unwrapping are improved significantly by masking layover and shadow regions during the phase unwrapping process

Target location performance evaluation of single SAR image of TH-2 satellite system

In order to evaluate the target location performance of a single SAR image of TH-2 satellites, this paper uses the theory and method of target location using the Range-Doppler model, Earth's ellipsoidal model and digital elevation model in the positioning experiments, and analyzes the experimental results from two aspects of predicting image point coordinate and positioning the ground target. Using three TH-2 SAR images in different regions to conduct experiment, it is concluded that the predicting image point accuracy is about 1 pixel and the ground target positioning accuracy is less than 2 m. The results show that the TH-2 satellite system has reliable system parameters and high precision positioning capability, which can provide reliable data for the ground target locating, the radar orthophoto image generation and other tasks

CEPC Technical Design Report -- Accelerator

International audienceThe Circular Electron Positron Collider (CEPC) is a large scientific project initiated and hosted by China, fostered through extensive collaboration with international partners. The complex comprises four accelerators: a 30 GeV Linac, a 1.1 GeV Damping Ring, a Booster capable of achieving energies up to 180 GeV, and a Collider operating at varying energy modes (Z, W, H, and ttbar). The Linac and Damping Ring are situated on the surface, while the Booster and Collider are housed in a 100 km circumference underground tunnel, strategically accommodating future expansion with provisions for a Super Proton Proton Collider (SPPC). The CEPC primarily serves as a Higgs factory. In its baseline design with synchrotron radiation (SR) power of 30 MW per beam, it can achieve a luminosity of 5e34 /cm^2/s^1, resulting in an integrated luminosity of 13 /ab for two interaction points over a decade, producing 2.6 million Higgs bosons. Increasing the SR power to 50 MW per beam expands the CEPC's capability to generate 4.3 million Higgs bosons, facilitating precise measurements of Higgs coupling at sub-percent levels, exceeding the precision expected from the HL-LHC by an order of magnitude. This Technical Design Report (TDR) follows the Preliminary Conceptual Design Report (Pre-CDR, 2015) and the Conceptual Design Report (CDR, 2018), comprehensively detailing the machine's layout and performance, physical design and analysis, technical systems design, R&D and prototyping efforts, and associated civil engineering aspects. Additionally, it includes a cost estimate and a preliminary construction timeline, establishing a framework for forthcoming engineering design phase and site selection procedures. Construction is anticipated to begin around 2027-2028, pending government approval, with an estimated duration of 8 years. The commencement of experiments could potentially initiate in the mid-2030s

CEPC Technical Design Report -- Accelerator

The Circular Electron Positron Collider (CEPC) is a large scientific project initiated and hosted by China, fostered through extensive collaboration with international partners. The complex comprises four accelerators: a 30 GeV Linac, a 1.1 GeV Damping Ring, a Booster capable of achieving energies up to 180 GeV, and a Collider operating at varying energy modes (Z, W, H, and ttbar). The Linac and Damping Ring are situated on the surface, while the Booster and Collider are housed in a 100 km circumference underground tunnel, strategically accommodating future expansion with provisions for a Super Proton Proton Collider (SPPC). The CEPC primarily serves as a Higgs factory. In its baseline design with synchrotron radiation (SR) power of 30 MW per beam, it can achieve a luminosity of 5e34 /cm^2/s^1, resulting in an integrated luminosity of 13 /ab for two interaction points over a decade, producing 2.6 million Higgs bosons. Increasing the SR power to 50 MW per beam expands the CEPC's capability to generate 4.3 million Higgs bosons, facilitating precise measurements of Higgs coupling at sub-percent levels, exceeding the precision expected from the HL-LHC by an order of magnitude. This Technical Design Report (TDR) follows the Preliminary Conceptual Design Report (Pre-CDR, 2015) and the Conceptual Design Report (CDR, 2018), comprehensively detailing the machine's layout and performance, physical design and analysis, technical systems design, R&D and prototyping efforts, and associated civil engineering aspects. Additionally, it includes a cost estimate and a preliminary construction timeline, establishing a framework for forthcoming engineering design phase and site selection procedures. Construction is anticipated to begin around 2027-2028, pending government approval, with an estimated duration of 8 years. The commencement of experiments could potentially initiate in the mid-2030s

CEPC Technical Design Report -- Accelerator

International audienceThe Circular Electron Positron Collider (CEPC) is a large scientific project initiated and hosted by China, fostered through extensive collaboration with international partners. The complex comprises four accelerators: a 30 GeV Linac, a 1.1 GeV Damping Ring, a Booster capable of achieving energies up to 180 GeV, and a Collider operating at varying energy modes (Z, W, H, and ttbar). The Linac and Damping Ring are situated on the surface, while the Booster and Collider are housed in a 100 km circumference underground tunnel, strategically accommodating future expansion with provisions for a Super Proton Proton Collider (SPPC). The CEPC primarily serves as a Higgs factory. In its baseline design with synchrotron radiation (SR) power of 30 MW per beam, it can achieve a luminosity of 5e34 /cm^2/s^1, resulting in an integrated luminosity of 13 /ab for two interaction points over a decade, producing 2.6 million Higgs bosons. Increasing the SR power to 50 MW per beam expands the CEPC's capability to generate 4.3 million Higgs bosons, facilitating precise measurements of Higgs coupling at sub-percent levels, exceeding the precision expected from the HL-LHC by an order of magnitude. This Technical Design Report (TDR) follows the Preliminary Conceptual Design Report (Pre-CDR, 2015) and the Conceptual Design Report (CDR, 2018), comprehensively detailing the machine's layout and performance, physical design and analysis, technical systems design, R&D and prototyping efforts, and associated civil engineering aspects. Additionally, it includes a cost estimate and a preliminary construction timeline, establishing a framework for forthcoming engineering design phase and site selection procedures. Construction is anticipated to begin around 2027-2028, pending government approval, with an estimated duration of 8 years. The commencement of experiments could potentially initiate in the mid-2030s