Performance Analysis of Ku/Ka Dual-Band SAR Altimeter from an Airborne Experiment over South China Sea

Satellite radar altimeters have been successfully used for sea surface height (SSH) measurement for decades, gaining great insight in oceanography, meteorology, marine geology, etc. To further improve the observation precision and spatial resolution, radar altimeters have evolved from real aperture to synthetic aperture, from the Ku-band to Ka-band. Future synthetic aperture radar (SAR) altimeter of the Ka-band is expected to achieve better performance than its predecessors. To verify the SAR altimeter data processing method and explore the system advantage of the Ka-band, a Ku/Ka dual-band SAR altimeter airborne experiment was carried out over South China Sea on 6 November 2021. Through dedicated hardware design, this campaign has acquired the Ku and Ka dual-band echo data simultaneously. The airborne data are processed to estimate the SSH retrieval precision after a series of procedures (including height compensation, range migration correction, multi-look processing, waveform re-tracking). To accustom to the airborne experiment design, a SAR echo model that fully considers both the attitude variation of the aircraft and the elliptical footprint of radar beam is established. The retrieved SSH data are compared with the public SSH data along the flight path at the experiment day, showing good consistence for both bands. By calculating the theoretical precision of waveform re-tracking and re-processing the dual-band airborne data into different bandwidths, it is demonstrated that the Ku/Ka precision ratio is possible to achieve 1.4 within the 27 km offshore area, which indicates that Ka-band has better performance

An Improved Altimeter in-Orbit Range Noise-Level Estimation Approach Based on Along-Track Differential Method

Satellite radar altimeters are advanced remote sensing devices that play an important role in observing the global marine environment. Accurately estimating the noise level of altimeter in-orbit ranging data is crucial for evaluating the payload performance, analyzing sea conditions, and monitoring data quality. In this study, we propose an approach based on the differential processing of along-track odd–even data sequences for altimeter in-orbit range noise-level estimation. Using the long-term along-track data sequence can notably improve the issue in the existing method in that the noise level is underestimated owing to the utilization of a relatively short data segment. On the basis of an analysis of the influence of low-frequency components on noise-level estimation, the mathematical formulas of the above differential method were deduced, and the efficacy of the approach in assessing the noise level of altimeter in-orbit data was demonstrated by simulation experiments. This method was used to estimate the noise levels of the 20 Hz datasets of Jason-3 and Sentinel-6, and the idea of the time-domain difference was extended to the frequency domain. The statistical results showed that the 20 Hz noise levels at the significant wave height (SWH) = 2 m were 7.41 cm (Jason-3 low-resolution (LR) mode), 6.66 cm (Sentinel-6 LR mode), and 3.13 cm (Sentinel-6 high-resolution (HR) mode). The power spectrum density analysis further verified its accuracy. By reprocessing the 20 Hz data of Sentinel-6 into 10, 5, and 1 Hz, the effectiveness of the along-track odd–even differential method to directly evaluate the noise level of 1 Hz data was explored, and the impact of ocean signals such as swells on noise-level estimation in synthetic aperture mode was discussed

An Improved Altimeter in-Orbit Range Noise-Level Estimation Approach Based on Along-Track Differential Method

Satellite radar altimeters are advanced remote sensing devices that play an important role in observing the global marine environment. Accurately estimating the noise level of altimeter in-orbit ranging data is crucial for evaluating the payload performance, analyzing sea conditions, and monitoring data quality. In this study, we propose an approach based on the differential processing of along-track odd–even data sequences for altimeter in-orbit range noise-level estimation. Using the long-term along-track data sequence can notably improve the issue in the existing method in that the noise level is underestimated owing to the utilization of a relatively short data segment. On the basis of an analysis of the influence of low-frequency components on noise-level estimation, the mathematical formulas of the above differential method were deduced, and the efficacy of the approach in assessing the noise level of altimeter in-orbit data was demonstrated by simulation experiments. This method was used to estimate the noise levels of the 20 Hz datasets of Jason-3 and Sentinel-6, and the idea of the time-domain difference was extended to the frequency domain. The statistical results showed that the 20 Hz noise levels at the significant wave height (SWH) = 2 m were 7.41 cm (Jason-3 low-resolution (LR) mode), 6.66 cm (Sentinel-6 LR mode), and 3.13 cm (Sentinel-6 high-resolution (HR) mode). The power spectrum density analysis further verified its accuracy. By reprocessing the 20 Hz data of Sentinel-6 into 10, 5, and 1 Hz, the effectiveness of the along-track odd–even differential method to directly evaluate the noise level of 1 Hz data was explored, and the impact of ocean signals such as swells on noise-level estimation in synthetic aperture mode was discussed

Development of a highly metastatic model that reveals a crucial role of fibronectin in lung cancer cell migration and invasion

<p>Abstract</p> <p>Background</p> <p>The formation of metastasis is the most common cause of death in patients with lung cancer. A major implement to understand the molecular mechanisms involved in lung cancer metastasis has been the lack of suitable models to address it. In this study, we aimed at establishing a highly metastatic model of human lung cancer and characterizing its metastatic properties and underlying mechanisms.</p> <p>Methods</p> <p>The human lung adeno-carcinoma SPC-A-1 cell line was used as parental cells for developing of highly metastatic cells by <it>in vivo </it>selection in NOD/SCID mice. After three rounds of selection, a new SPC-A-1sci cell line was established from pulmonary metastatic lesions. Subsequently, the metastatic properties of this cell line were analyzed, including optical imaging of <it>in vivo </it>metastasis, immunofluorescence and immunohistochemical analysis of several epithelial mesenchymal transition (EMT) makers and trans-well migration and invasion assays. Finally, the functional roles of fibronectin in the invasive and metastatic potentials of SPC-A-1sci cells were determined by shRNA analysis.</p> <p>Results</p> <p>A spontaneously pulmonary metastatic model of human lung adeno-carcinoma was established in NOD/SCID mice, from which a new lung cancer cell line, designated SPC-A-1sci, was isolated. Initially, the highly metastatic behavior of this cell line was validated by optical imaging in mice models. Further analyses showed that this cell line exhibit phenotypic and molecular alterations consistent with EMT. Compared with its parent cell line SPC-A-1, SPC-A-1sci was more aggressive <it>in vitro</it>, including increased potentials for cell spreading, migration and invasion. Importantly, fibronectin, a mesenchymal maker of EMT, was found to be highly expressed in SPC-A-1sci cells and down-regulation of it can decrease the <it>in vitro </it>and <it>in vivo </it>metastatic abilities of this cell line.</p> <p>Conclusions</p> <p>We have successfully established a new human lung cancer cell line with highly metastatic potentials, which is subject to EMT and possibly mediated by increased fibronectin expression. This cell line and its reproducible <it>s.c</it>. mouse model can further be used to identify underlying mechanisms of lung cancer metastasis.</p