Abstract:In traditional localization methods for synthetic aperture radar (SAR), the range sum estimation and Doppler centroid estimation (DCE) are required. The DCE error can influence the localization accuracy greatly. In addition, the target height information cannot be obtained by these methods. In this paper, a three-dimensional localization method for multistatic SAR based on the numerical range-Doppler (RD) algorithm and entropy minimization principle is proposed. In this method, the raw data from each transmitter and receiver (T/R) pair are focused by the numerical RD algorithm with the initial location value of the reference target. Then, Newton iteration is used to solve the target location value with the information of the bistatic range sum (BRS) in different SAR images with respect to different T/R pairs. Generally, the initial location value of the reference target is not accurate, and it can influence the imaging quality and accuracy of other target locations. We use entropy to measure image quality and iterate imaging with the new location value of the reference target, until the entropy gets the minimum value. Therefore, we can get the optimal location value of the reference target, which can make image entropy reach the minimum. Finally, all targets can be located by the Newton iteration method with their BRS in each T/R pair that are obtained from the images with minimum entropy. Compared with traditional localization methods for monostatic SAR, the proposed method not only effectively eliminates the influences of DCE errors, but also can get the target height information. Therefore, it improves the localization accuracy and can achieve three-dimensional localization. The effectiveness of the localization approach is validated by a numerical simulation experiment.
which is at a level that is comparable to the state-of-the-art silicon solar cells. Presently, the potential for mass production of perovskite solar modules (PSMs) is being intensively explored, and the PCE is steadily improving (Figure S1, Supporting Information). The development of high throughput manufacturing technologies is crucial to fulfilling the prerequisites of mass production of photovoltaic panels with short tact times and good reproducibility. High precision, fine resolution laser scribing technology has the advantages of low cost, fast operating speed, and small area loss, making it far superior to other structuring methods to realize commercial-scale production of high-performance thin film solar cells. [5] The laser photons are absorbed by the solar cell materials and their energy is first absorbed by free electrons, and then transferred to the lattice, leading to material gasification. [6] Thus, the longer the pulse duration, that is, the more the laser pulse exceeds the duration of the electron-lattice interaction, the more likely it is to generate a larger heat-affected zone (HAZ), as excess energy diffuses into the material in the form of lattice vibrations. Therefore, lasers generating ultrashort (picosecond or femtosecond) pulses are more attractive for processing devices that are sensitive to the presence of a HAZ rather than the short pulse laser (nanosecond). Organic-inorganic hybrid PSCs have been developed for over 10 years, and have reached the stage of industrialization. [7] However, in-depth research on laser processing for module manufacturing is lacking. For instance, the question of whether picosecond (ps) or femtosecond (fs) lasers are critically required to fabricate a high geometric filling factor (GFF) and photovoltaic performance PSMs has not been studied systematically.Ballif et al. first reported laser-scribed PSMs in 2015 with a GFF of 84% by using a nanosecond (ns) pulse laser. [8] In 2021, Huang et al. gained an active area PCE of 20.4% for a PSM by utilizing a femtosecond (fs) pulse laser, starting from a PCE of PSC of 23.35%. [9] Recently, an active area PCE of 21.4% was achieved by Nazeeruddin et al. for their PSMs, while the GFF was as high as 90.2%. [10] Seok et al. achieved an aperture area efficiency of 20.4% and a GFF of 94.36% by using a ps pulse laser. [11] It can be concluded that the improvement of aperture area PCE's of PSMs still suffers from considerable cell-tomodule (CTM) efficiency losses and/or low GFF even when Overcoming cell-to-module (CTM) efficiency losses is indispensable to realize large-area high-efficiency perovskite photovoltaic devices for commercialization. Laser scribing technology is used to fabricate perovskite modules, but it does not seem to solve the problem of high-quality interconnection and high geometric filling factor (GFF), which are the prerequisites for overcoming CTM losses. In reality, what kind of laser technology is needed to fabricate highefficiency perovskite solar modules is still an open question. Herein, this work dem...
In traditional localization methods for Synthetic Aperture Radar (SAR), the bistatic range sum (BRS) estimation and Doppler centroid estimation (DCE) are needed for the calculation of target localization. However, the DCE error greatly influences the localization accuracy. In this paper, a localization method for multistatic SAR based on convex optimization without DCE is investigated and the influence of BRS estimation error on localization accuracy is analysed. Firstly, by using the information of each transmitter and receiver (T/R) pair and the target in SAR image, the model functions of T/R pairs are constructed. Each model function’s maximum is on the circumference of the ellipse which is the iso-range for its model function’s T/R pair. Secondly, the target function whose maximum is located at the position of the target is obtained by adding all model functions. Thirdly, the target function is optimized based on gradient descent method to obtain the position of the target. During the iteration process, principal component analysis is implemented to guarantee the accuracy of the method and improve the computational efficiency. The proposed method only utilizes BRSs of a target in several focused images from multistatic SAR. Therefore, compared with traditional localization methods for SAR, the proposed method greatly improves the localization accuracy. The effectivity of the localization approach is validated by simulation experiment.
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