5 research outputs found
SaaFormer: Spectral-spatial Axial Aggregation Transformer for Hyperspectral Image Classification
Hyperspectral images (HSI) captured from earth observing satellites and
aircraft is becoming increasingly important for applications in agriculture,
environmental monitoring, mining, etc. Due to the limited available
hyperspectral datasets, the pixel-wise random sampling is the most commonly
used training-test dataset partition approach, which has significant overlap
between samples in training and test datasets. Furthermore, our experimental
observations indicates that regions with larger overlap often exhibit higher
classification accuracy. Consequently, the pixel-wise random sampling approach
poses a risk of data leakage. Thus, we propose a block-wise sampling method to
minimize the potential for data leakage. Our experimental findings also confirm
the presence of data leakage in models such as 2DCNN. Further, We propose a
spectral-spatial axial aggregation transformer model, namely SaaFormer, to
address the challenges associated with hyperspectral image classifier that
considers HSI as long sequential three-dimensional images. The model comprises
two primary components: axial aggregation attention and multi-level
spectral-spatial extraction. The axial aggregation attention mechanism
effectively exploits the continuity and correlation among spectral bands at
each pixel position in hyperspectral images, while aggregating spatial
dimension features. This enables SaaFormer to maintain high precision even
under block-wise sampling. The multi-level spectral-spatial extraction
structure is designed to capture the sensitivity of different material
components to specific spectral bands, allowing the model to focus on a broader
range of spectral details. The results on six publicly available datasets
demonstrate that our model exhibits comparable performance when using random
sampling, while significantly outperforming other methods when employing
block-wise sampling partition.Comment: arXiv admin note: text overlap with arXiv:2107.02988 by other author
Investigation on Electromagnetic Models of High-Speed Solenoid Valve for Common Rail Injector
A novel formula easily applied with high precision is proposed in this paper to fit the B-H curve of soft magnetic materials, and it is validated by comparison with predicted and experimental results. It can accurately describe the nonlinear magnetization process and magnetic saturation characteristics of soft magnetic materials. Based on the electromagnetic transient coupling principle, an electromagnetic mathematical model of a high-speed solenoid valve (HSV) is developed in Fortran language that takes the saturation phenomena of the electromagnetic force into consideration. The accuracy of the model is validated by the comparison of the simulated and experimental static electromagnetic forces. Through experiment, it is concluded that the increase of the drive current is conducive to improving the electromagnetic energy conversion efficiency of the HSV at a low drive current, but it has little effect at a high drive current. Through simulation, it is discovered that the electromagnetic energy conversion characteristics of the HSV are affected by the drive current and the total reluctance, consisting of the gap reluctance and the reluctance of the iron core and armature soft magnetic materials. These two influence factors, within the scope of the different drive currents, have different contribution rates to the electromagnetic energy conversion efficiency
Centimeter-Level Orbit Determination for TG02 Spacelab Using Onboard GNSS Data
Tiangong-2, the second Chinese manned spacecraft, was launched into low Earth orbit on 15 September 2016. The dual-frequency geodetic GNSS receiver equipped on it is supporting a number of scientific experiments in orbit. This paper uses the onboard GNSS data from 3–31 December 2016 (in the attitude mode of three-axis Earth-pointing stabilization) to analyze the data quantity, as well as the code multipath error. Then, the dynamic and reduced-dynamic methods are adopted to perform the post Precise Orbit Determination (POD) based on the carrier phase measurements, respectively. After that, the orbit accuracy is evaluated using a number of tests, which include the analysis of observation residuals, Overlapping Orbit Differences (OODs), orbit comparison between dynamic and reduced-dynamic and Satellite Laser Ranging (SLR) validation. The results show that: (1) the average Root Mean Square (RMS) of the on-board GNSS phase fitting residuals is 8.8 mm; (2) regarding the OODs determined by the reduced-dynamic method, the average RMS in radial (R), along-track (T) and cross-track (N) directions is 0.43 cm, 1.34 cm and 0.39 cm, respectively, and there are no obvious system errors; (3) the orbit accuracy of TG02 determined by the reduced-dynamic method is comparable to that of the dynamic method, and the average RMS of their differences in R, T, N and 3D directions is 3.05 cm, 3.60 cm, 2.52 cm and 5.40 cm, respectively; (4) SLR data are used to validate the reduced-dynamic orbits, and the average RMS along the station-satellite direction is 1.94 cm. It can be seen that both of these two methods can meet the demands of 3D centimeter-level orbit determination for TG02