In order to develop new energetic materials with high energy and low sensitivity, a series of nitrogen-rich energetic salts based on 3-nitramino-4-tetrazolefurazan were conveniently synthesized through nitration, neutralization and metathesis reaction. All energetic salts were fully characterized by NMR (¹H, ¹³C), IR and elemental analysis. Furthermore, ammonium salt (2) was confirmed by ¹⁵N NMR and hydroxylammonium salt (5) was confirmed by single-crystal X-ray diffraction. Salt 5 crystallized in triclinic space group P with four hydroxylammonium cations and two NATF anions per unit cell at a density of 1.815 g cm⁻³. The densities of the salts are in the range of 1.621 (6) to 1.815 g cm⁻³ (5). Due to the two nitrogen-rich cations in the salts, they show high positive enthalpies of formation falling between 299.2 kJ mol⁻¹ (2) and 1040.6 kJ mol⁻¹ (9). All the salts show good thermal stabilities with the decomposition temperatures ranging from 203 °C (4) to 284 °C (6). The impact sensitivities of the energetic salts lie between 5 J (2 and 5) and >40 J (6, 7, 8) and their friction sensitivities range from 108 N (4) to >360 N (6). Their detonation performances were calculated according to Kamlet–Jacobs equations. The detonation pressures of the synthesized energetic salts were found to be in the range of 21.1 GPa (6) to 34.7 GPa (5) and their detonation velocities are between 7117 m s⁻¹ (6) and 8826 m s⁻¹ (5).

Processing high-squinted spaceborne SAR data in the sliding-spotlight mode is a challenging task due to azimuth spectral aliasing and range-azimuth coupling for frequency-domain imaging algorithms, and most critically, the variation of Doppler parameters causes significant reduction in the depth-of-azimuth-focus (DOAF). In this article, a novel imaging algorithm is proposed for focusing high-squinted spaceborne SAR data in the sliding-spotlight mode. First, linear range walk correction (LRWC) and range frequency-dependent derotation are applied to remove the coupling of range frequency with the Doppler parameters. Then, a modified range migration algorithm (RMA) is derived for accurate focusing. The deramp operation combined with improved nonlinear chirp scaling (INCS) is employed for solving the aliasing problem of azimuth time and extending the DOAF in the third step. Finally, geometry distortion caused by LRWC is corrected. Simulation results are provided to demonstrate the effectiveness of the proposed algorithm.

Interferometric phase filtering is a crucial step in multibaseline interferometric synthetic aperture radar (InSAR). Current multibaseline interferometric phase filtering methods mostly follow methods of single-baseline InSAR and do not bring its data superiority into full play. The joint filtering of multibaseline InSAR based on statistics is proposed in this paper. We study and analyze the fourth-order statistical quantity of interferometric phase: kurtosis. An empirical assumption that the kurtosis of interferograms with different baselines keeps constant is proposed and is named as the baseline-invariant property of kurtosis in this paper. Some numerical experiments and rational analyses confirm its validity and universality. The noise level estimation of nature images is extended to multibaseline InSAR by dint of the baseline-invariant property of kurtosis. A filtering method based on the non-subsampled shearlet transform (NSST) and Wiener filter with estimated noise variance is proposed then. Firstly, multi-scaled and multi-directional coefficients of interferograms are obtained by NSST. Secondly, the noise variance is represented as the solution of a constrained non-convex optimization problem. A pre-thresholded Wiener filtering with estimated noise variance is employed for shrinking or zeroing NSST coefficients. Finally, the inverse NSST is utilized to obtain the filtered interferograms. Experiments on simulated and real data show that the proposed method has excellent comprehensive performance and is superior to conventional single-baseline filtering methods.