Photoluminescence property of polymer–rare earth complexes containing acetaldehyde/aminophenol type bidentate Schiff base ligand

<p>Acetaldehyde was introduced onto the side chains of polysulfone, and then Schiff base reactions were carried out between the introduced acetaldehyde and ortho-aminophenol (OAP) or meta-aminophenol (MAP). Two bidentate Schiff base (B) ligands of acetaldehyde/aminophenol type, OAPB and MAPB, were bonded on the side chains of polysulfone, and two new bidentate Schiff base ligand functionalized-polysulfones, PSF-OAPB and PSF-MAPB, were obtained. The triplet state energies of OAPB and MAPB are well matched with the resonant level energy of Tb(III), and the Tb(III) complexes emit the strong characteristic fluorescence of Tb(III) (green luminescence). Complexes of Eu(III) have no fluorescence emission because of the mismatching of the energy levels. In comparison, the fluorescence intensity of the binary complex PSF-(MAPB)₃-Tb(III) is stronger than that of the binary complex PSF-(OAPB)₃-Tb(III) because of the structured difference of the chelating ring. The ternary complexes PSF-(MAPB)₃-Tb(III)-(Phen)₁ (Phen represents 1,10-phenanthroline) and PSF-(OAPB)₃-Tb(III)-(Phen)₁ have stronger fluorescence emissions than the corresponding binary complexes. The fluorescence emission intensities of solid films of the complexes are stronger than that of their solutions. The prepared luminescent polymer-Tb(III) complexes containing acetaldehyde/aminophenol type bidentate Schiff base ligands have very high quantum yields (80–86%), reflecting the high intramolecular energy transfer efficiencies from the ligands to Tb(III).</p

Analysis and Mitigation of Crosstalk Effect on Coastal GNSS-R Code-Level Altimetry Using L5 Signals from QZSS GEO

Coastal Global Navigation Satellite System Reflectometry (GNSS-R) can be used as a valuable supplement for conventional tide gauges, which can be applied for marine environment monitoring and disaster warning. Incidentally, an important problem in dual-antenna GNSS-R altimetry is the crosstalk effect, which means that the direct signal leaks into the down-looking antenna dedicated to the reflected signals. When the path delay between the direct and reflected signals is less than one chip length, the delay waveform of the reflected signal is distorted, and the code-level altimetry precision decreases consequently. To solve this problem, the author deduced the influence of signal crosstalk on the reflected signal structure as the same as the multipath effect. Then, a simulation and a coastal experiment are performed to analyze the crosstalk effect on code delay measurements. The L5 signal transmitted by the Quasi-Zenith Satellite System (QZSS) from a geosynchronous equatorial orbit (GEO) satellite is used to avoid the signal power variations with the elevation, so that high-precision GNSS-R code altimetry measurements are achieved in the experiment. Theoretically and experimentally, we found there exists a bias in proportion to the power of the crosstalk signals and a high-frequency term related to the phase delay between the direct and reflected signals. After weakening the crosstalk by correcting the delay waveform, the results show that the RMSE between 23-h sea level height (SSH) measurements and the in-situ observations is about 9.5 cm

Analysis and Mitigation of Crosstalk Effect on Coastal GNSS-R Code-Level Altimetry Using L5 Signals from QZSS GEO

Coastal Global Navigation Satellite System Reflectometry (GNSS-R) can be used as a valuable supplement for conventional tide gauges, which can be applied for marine environment monitoring and disaster warning. Incidentally, an important problem in dual-antenna GNSS-R altimetry is the crosstalk effect, which means that the direct signal leaks into the down-looking antenna dedicated to the reflected signals. When the path delay between the direct and reflected signals is less than one chip length, the delay waveform of the reflected signal is distorted, and the code-level altimetry precision decreases consequently. To solve this problem, the author deduced the influence of signal crosstalk on the reflected signal structure as the same as the multipath effect. Then, a simulation and a coastal experiment are performed to analyze the crosstalk effect on code delay measurements. The L5 signal transmitted by the Quasi-Zenith Satellite System (QZSS) from a geosynchronous equatorial orbit (GEO) satellite is used to avoid the signal power variations with the elevation, so that high-precision GNSS-R code altimetry measurements are achieved in the experiment. Theoretically and experimentally, we found there exists a bias in proportion to the power of the crosstalk signals and a high-frequency term related to the phase delay between the direct and reflected signals. After weakening the crosstalk by correcting the delay waveform, the results show that the RMSE between 23-h sea level height (SSH) measurements and the in-situ observations is about 9.5 cm

A Coastal Experiment for GNSS-R Code-Level Altimetry Using BDS-3 New Civil Signals

High temporal and spatial resolutions are the key advantages of the global navigation satellites system-reflectometry (GNSS-R) technique, while low precision and instabilities constrain its development. Compared with conventional Ku/C band nadir-looking radar altimetry, the precision of GNSS-R code-level altimetry is restricted by the smaller bandwidth and the lower transmitted power of the signals. Fortunately, modernized GNSS broadcast new open-available ranging codes with wider bandwidth. The Chinese BDS-3 system was built on 31 July 2020; its inclined geostationary orbit and medium circular orbit satellites provide B1C and B2a public navigation service signals in the two frequency bands of B1 and B2. In order to investigate their performance on GNSS-R code-level altimetry, a coastal experiment was conducted on 5 November 2020 at a trestle of Weihai in the Shandong province of China. The raw intermediate frequency data with a 62 MHz sampling rate were collected and post-processed to solve the sea surface height every second continuously for over eight hours. The precisions were evaluated using the measurements from a 26 GHz radar altimeter mounted on the same trestle near our GNSS-R setup. The results show that a centimeter-level accuracy of GNSS-R altimetry—based on B1C code after the application of the moving average—can be achieved, while for B2a code, the accuracy is about 10 to 20 cm

Analysis and Performance Evaluation of BDS-3 Code Ranging Accuracy Based on Raw IF Data from a Zero-Baseline Experiment

China’s BDS-3 global navigation satellite system has been built and is providing official open Positioning, Navigation, and Timing (PNT) service with full operational capability (FOC) since July 2020. The main new civil B1C and B2a ranging code signals are broadcasted on the two carriers with central frequencies of 1575.42 MHz and 1176.45 MHz, which were shared by other GNSSs. Compared with traditional signals, such as GPS L1 C/A and BDS B1I, the new civil signals have better modulation and wider bandwidth to be expected to achieve a better range performance. In order to evaluate code ranging accuracies directly, a zero-baseline experiment using a geodetic GNSS antenna and a four-channel intermediate frequency (IF) signal recorder was conducted. Two channels were used to receive the signals with a central frequency of 1575.42 MHz at a 62 MHz sampling rate, and the other two channels are for 1176.45 MHz. The raw IF data were post-processed using a software-defined receiver (SDR) to compute the code signal path differences between two channels with the same frequencies. Compared with the traditional hardware receiver, SDR has the characteristics of flexible use and good operability, but its running speed is slow. The root-mean-square (RMS) and bias values of the path differences from BDS B1C, BDS B2a, and GPS L5C were used to evaluate their accuracies. The results show that there is a weak negative correlation between the satellite elevation and the ranging accuracy when the satellite elevation ranges from 30° to 90°. The ranging accuracy of the B1C signal is lower than that of B2a, which may be caused by different code rates, bandwidth, and signal structure. The GPS L5C is used for precision analysis as a comparison. It shows that the code signal path differences accuracy of L5C is close to the B2a