摘要：A novel X-band unit cell structure with improved bandwidth performance for single-layer microstrip reflectarray antenna is proposed. The new element structure consists of two circular rings, each with a pair of gaps, and two phase-delay lines are attached to the outer ring to provide the required phase shift. A 9� center-fed reflectarray antenna operating at 10 GHz is designed to validate the broadband performance of the proposed unit cell. Simulated results show 20% 1-dB gain bandwidth and 38.5% 3-dB gain bandwidth. The maximum gain at 10 GHz is 20.1 dB, which is equivalent to 40 % efficiency.
摘要：Deorientation plays an important role in polarimetric synthetic aperture radar (PolSAR) target decomposition, terrain classification, and geophysical parameters retrieval. The existing deorientation method roughly rotates the target by an average/mixed orientation angle (OA) about the line of radar sight. However, regarding the complex high-entropy mixed scatterer, which usually comprises several comparable sub-scatterers with different OAs, the average/mixed OA is obviously insufficient to account for the diverse OAs’ reality. To address this, a novel PolSAR data deorientation method is proposed in this letter. The proposed method deorients a mixed scatterer by reconstructing the underlying sub-scatterers using the eigenvalue-based Cloude–Pottier decomposition first, and then compensates the OA of each reconstructed sub-scatterer using Huynen’s desying operation, respectively. One important feature of the proposed method is that it is consistent with Huynen’s desying operation that the real part of the (1, 3) element of the deoriented coherency matrix should be zero. The proposed method provides a fine deorientation for mixed targets, and is especially suitable for the extraction of oriented urban regions. Comparative experiments with the existing method on RADARSAT-2 PolSAR data demonstrate the excellent deorientation performance of the proposed method. © 2016 The Author(s). Published by Informa UK Limited, trading as Taylor & Francis Group.
摘要：A 1-D interferometric system at 1.4GHz, 6.9GHz, 18.7 GHz and 23.8GHz combined with a scatterometer at 1.26GHz, called microwave imager combined active/passive (MICAP), has been proposed to retrieve sea surface salinity (SSS) and to reduce geophysical errors due to surface roughness and sea surface temperature (SST). The MICAP will be a candidate payload onboard the Ocean Salinity Satellite of China. The sensitivity of active/passive microwave observations to SSS, SST and wind is analyzed and the stability requirement of the instruments is estimated, with the objective of designing an optimized satellite instrument, dedicated to an "all-weather" estimate of the SSS with high accuracy from space.
摘要：The authors propose a novel compressive sensing (CS)-based Dechirp-Keystone algorithm (DKA) for synthetic aperture radar (SAR) moving target imaging, which is called the CS-DKA. The DKA can focus on moving targets in range-Doppler domain efficiently through only keystone transform (KT), complex multiplication and Fourier transform (FT)/inverse Fourier transform (IFT) operations. It has been shown that the non-interpolation implementation of KT can be expressed by an orthonormal basis, and it is known that the complex multiplication and FT/IFT are linear and invertible; therefore, the Dechirp-Keystone operator (DKO) is also linear and invertible. In the proposed algorithm, the authors take the inverse of DKO (IDKO) rather than the exact SAR echo model to construct the representation basis in the CS frame owing to its high implementation efficiency. After that, a random transmitting/receiving scheme is considered, to implement the down-sampling operation, and then reconstruct the moving target image by solving a regularisation problem. Both simulated and real SAR data are processed to show that the CS-DKA with down-sampled data can focus the target as well as the conventional DKA does with full data, and at the same time can achieve much lower sidelobes.
摘要：This paper proposes a burst model of chaotic noise signals with randomly stepped carrier frequencies for velocity estimation and high-resolution range imaging of high-speed moving targets. The random stepping of carrier frequencies is controlled by a combination chaotic map (CCM), which is generated by embedding a Logistic map into a Bernoulli map. The baseband noise signal adopts the CCM based frequency-modulation (CCM-FM) signal, which has good randomness and a thumbtack ambiguity function as well. The velocity estimation includes a coarse search and a precise search, where the coarse search is conducted with a fixed step to makes the velocity deviation less than the velocity resolution, while the precise search adopts the Golden Section Search (GSS) algorithm to get an accurate estimation of velocity. What should be emphasized is that the velocity estimation process can be completed with just a burst of subpulses. Then the spectra are coherently synthesized to obtain ultra-wide bandwidth and high-resolution range imaging. Finally, numerical simulations demonstrate a good performance of the proposed signal model and the processing algorithm.
摘要：As we know, a moving target’s azimuth shift in synthetic aperture radar (SAR) image is proportional to the projected velocity of its across-track velocity in the slant-range plane. Therefore, we can relocate the moving target in SAR image after estimating its velocity. However, when the Doppler ambiguity occurs due to the limitation of the SAR system’s pulse repetition frequency (PRF), this relationship will not hold any more, in this case, we cannot relocate the moving target to the right position. The Doppler spectrum of a moving target with arbitrary velocity may entirely situate in a PRF band or span in two neighboring PRF bands. In this paper, we conduct a detailed theoretical analysis on the moving target’s azimuth shift for these two scenarios. According to the derived formulas, one can relocate a moving target with arbitrary velocity to the right position no matter the Doppler ambiguity occurs or not. Simulated data are processed to validate the analysis. © 2015 Electromagnetics Academy. All rights reserved.
摘要：In order to satisfy a high resolution for the measurement of snow water equivalent, we use the system of using the dual frequency(X-band 9.6GHz and Ku-band 17GHz) and full polarization. This paper discusses the various system options(scanning pencil-beam, high PRF, high SNR) and tradeoffs considered for improving the azimuth resolution of scatterometer are required.
摘要：GNSS buoys are innovative ocean instruments, and can provide calibrations of the sea surface height and significant wave height (SWH) products of satellite altimeters. This paper investigated the principles of the wave retrieval by GNSS buoys, and proposed a method of calibration of altimeter SWH product by GNSS buoys. The error sources in the calibration procedure were analyzed. Ocean calibration campaigns were implemented to measure the SWH at the HY-2 altimeter nadir points, and acquired a SWH bias of +7.92 +/- 5.04 cm using four-parameters retracking algorithm. The SWH bias was +20.37 +/- 12.79 cm base on the HY-2 operational SWH products. The calibration campaigns showed that, GNSS buoys could serve for the satellite altimeter SWH calibration under low sea state condition, and the four-parameters retracking algorithm outperformed the conventional three-parameters retracking algorithm in accuracy and consistency, at least for SWH retrieving.
摘要：An airborne delay Doppler altimeter was flown in autumn 2014. A calibration suite including a GNSS buoy, two tide gauges and two GPS stations were established. An experiment was carried out to test the GNSS buoy as a whole under dynamic ocean condition, to validate its performance and accuracy via the inter-comparison of tide gauges, and to demonstrate the altimetry calibration methods and to estimate the altimeter system bias. This paper presented some methods and results. The GNSS buoy system was proven to have the ability of measuring the sea surface height within 1cm, and the altimeter system bias had a consistency of centimeter level.