Vector Current Measurement Using Doppler Scatterometry with Optimally Selected Observation Azimuths
Abstract
:1. Introduction
2. The Principle of Ocean Current Velocity Measurement Using Doppler Scatterometry
3. The Proposed Ocean Current Velocity Determination Method
3.1. Data Simulation Module
Algorithm 1 Data simulation for Doppler scatterometer. |
1: Input: The local incident angles ${\theta}_{1}$ and ${\theta}_{2}$, the observation azimuths ${\varphi}_{1}$, ${\varphi}_{2}$, |
2: and ${\varphi}_{3}$, polarization mode ${p}_{1}$ and ${p}_{2}$, wind field parameters ${U}_{wind}$ and ${\varphi}_{wind}$, the |
3: current field parameters ${V}_{current}$ and ${\varphi}_{current}$. |
4: Output: The simulated interference phase difference measurements $\Delta {\mathsf{\Phi}}_{M1}$, |
5: $\Delta {\mathsf{\Phi}}_{M2}$, and $\Delta {\mathsf{\Phi}}_{M3}$. |
6: ① For an observation position on the sea surface, radial current speeds ${V}_{R1}$, ${V}_{R2}$, |
7: and ${V}_{R3}$ in three different observation azimuths ${\varphi}_{1}$$,{\varphi}_{2}$, and ${\varphi}_{3}$ are calculated |
8: using Equation (1) according to the given ocean current velocity. |
9: ② The echo-Doppler spectra along three observation azimuths are calculated using |
10: the Doppler spectrum model [24] with ${\varphi}_{1}$$,{\varphi}_{2}$, ${\varphi}_{3}$, ${U}_{wind}$, ${\varphi}_{wind}$, ${V}_{R1}$$,{V}_{R2}$$,{V}_{R3}$, |
11: ${\theta}_{1}$, ${\theta}_{2}$, ${p}_{1}$ and ${p}_{2}$ as input parameters. The corresponding Doppler spectra for |
12: ${V}_{R1}=0$$,{V}_{R2}=0$ and ${V}_{R3}=0$ can also be obtained. |
13: ③ Based on the obtained Doppler spectra, the Doppler center frequencies can be |
14: calculated using Equation (3). Then the Doppler frequency shifts $\Delta {f}_{{M}_{Doppler}1}$, |
15: $\Delta {f}_{{M}_{Doppler}2}$ and $\Delta {f}_{{M}_{Doppler}3}$ can be obtained based on Equation (4). |
16: ④ The ideal echo interference phase differences $\Delta {\tilde{\mathsf{\Phi}}}_{1}$$,\Delta {\tilde{\mathsf{\Phi}}}_{2}$$\mathrm{and}\Delta {\tilde{\mathsf{\Phi}}}_{3}$ for obser- |
17: vation azimuths ${\varphi}_{1}$$,{\varphi}_{2}$ and ${\varphi}_{3}$ can be respectively calculated using Equation (2) |
18: with the obtained $\Delta {f}_{{M}_{Doppler}1}$, $\Delta {f}_{{M}_{Doppler}2}$ and $\Delta {f}_{{M}_{Doppler}3}$. |
19: ⑤ The radial current speed error model is used to generate the radial current speed |
20: error $\Delta {V}_{R1}$$,\Delta {V}_{R2}$ and $\Delta {V}_{R3}$ in observation azimuths ${\varphi}_{1}$$,{\varphi}_{2}$ and ${\varphi}_{3}$. Then |
21: Equation (6) is applied to obtain the interference phase difference $\Delta {\mathsf{\Phi}}_{{V}_{R1}}$$,\Delta {\mathsf{\Phi}}_{{V}_{R2}}$ |
22: and $\Delta {\mathsf{\Phi}}_{{V}_{R3}}$ caused by $\Delta {V}_{R1}$$,\Delta {V}_{R2}$ and $\Delta {V}_{R3}$. |
23: ⑥ The simulated interference phase difference measurements $\Delta {\mathsf{\Phi}}_{M1}$$,\Delta {\mathsf{\Phi}}_{M2}$ and |
24: $\Delta {\mathsf{\Phi}}_{M3}$ are calculated using Equation (7) with the obtained $\Delta {\tilde{\mathsf{\Phi}}}_{1}$ and $\Delta {\mathsf{\Phi}}_{{V}_{R1}}$$,\Delta {\tilde{\mathsf{\Phi}}}_{2}$ |
25: and $\Delta {\mathsf{\Phi}}_{{V}_{R2}}$$,\Delta {\tilde{\mathsf{\Phi}}}_{3}$ and $\Delta {\mathsf{\Phi}}_{{V}_{R3}}$. |
3.2. Radial Current Speed Inversion Module
3.3. Vector Current Velocity Determination Module
3.3.1. Proposed Vector Current Velocity Determination Method
3.3.2. A Method for Optimal Observation Azimuth Selection
Algorithm 2 Vector current velocity estimation based on optimally selected observation azimuths. |
1: Input: The observation azimuths ${\varphi}_{1}$$,{\varphi}_{2}$, and ${\varphi}_{3}$, the measured interference phase |
2: difference $\Delta {\mathsf{\Phi}}_{M1}$$,\Delta {\mathsf{\Phi}}_{M2}$, and $\Delta {\mathsf{\Phi}}_{M3}$. |
3: Output: The vector current velocity at an observation position. |
4: ① According to $\Delta {\mathsf{\Phi}}_{M1}$$,\Delta {\mathsf{\Phi}}_{M2}$, and $\Delta {\mathsf{\Phi}}_{M3}$, the radial current speeds ${V}_{R1}^{\prime}$$,{V}_{R2}^{\prime}$, and |
5: ${V}_{R3}^{\prime}$ in ${\varphi}_{1}$$,{\varphi}_{2}$, and ${\varphi}_{3}$ are estimated using the interference phase difference |
6: matching method (see Equation (8)). |
7: ② Any two radial current speeds from two different observation azimuths are se- |
8: lected to determine a vector current velocity using Equations (13) and (14). The |
9: obtained current direction ${\varphi}_{p}$ is used as a preliminary estimation of the current |
10: direction. |
11: ③ The optimal observation azimuths ${\varphi}_{Opt1}$ and ${\varphi}_{Opt2}$ are determined using |
12: Equations (15) and (16) with ${\varphi}_{1}$$,{\varphi}_{2}$$,{\varphi}_{3}$, and ${\varphi}_{p}$ as input. |
13: ④ The final vector current velocity is obtained using Equations (13) and (14) with |
14: radial current speeds obtained from observation azimuths ${\varphi}_{Opt1}$ and ${\varphi}_{Opt2}$. |
4. Experimental Results
4.1. Data Simulation Results and Analysis
4.2. Verification of the Proposed Vector Current Velocity Determination Method
4.3. Current Velocity Inversion Results and Analysis
5. Conclusions
Author Contributions
Funding
Data Availability Statement
Acknowledgments
Conflicts of Interest
References
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Application | Coverage | Measurement Accuracy (m/s) | Time Resolution (h) | Spatial Resolution (km) |
---|---|---|---|---|
Weather Service | Global | 0.1 | 6 | 12.5 |
Ocean Service | Global | 0.1 | 1 | 12.5 |
Ship Routing | Global | 0.05 | 1 | 1 |
Pollution | Local | 0.1 | 1 | 0.1 |
Fisheries Management | Local | 0.1 | 6 | 1 |
Parameters | Specification |
---|---|
Satellite Velocity | 7373 m/s |
Orbit Altitude | 963 km |
Observation Azimuth | 10°, 30°, and 170° |
Local Incident Angle | ${41}^{\xb0}(\mathrm{H}\mathrm{H})/{48}^{\xb0}(\mathrm{V}\mathrm{V})$ |
Antenna Incident Angle | ${35}^{\xb0}(\mathrm{H}\mathrm{H})/{41}^{\xb0}(\mathrm{V}\mathrm{V})$ |
Antenna Gain | 48 dB |
Rotation Rate | 18 rpm |
Carrier Frequency | 13.5 GHz |
PRF | 12 kHz |
Pulse Bandwidth | 5 MHz |
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Sun, W.; Wang, Q.; Huang, W.; Fan, C.; Dai, Y. Vector Current Measurement Using Doppler Scatterometry with Optimally Selected Observation Azimuths. Remote Sens. 2021, 13, 4263. https://doi.org/10.3390/rs13214263
Sun W, Wang Q, Huang W, Fan C, Dai Y. Vector Current Measurement Using Doppler Scatterometry with Optimally Selected Observation Azimuths. Remote Sensing. 2021; 13(21):4263. https://doi.org/10.3390/rs13214263
Chicago/Turabian StyleSun, Weifeng, Qing Wang, Weimin Huang, Chenqing Fan, and Yongshou Dai. 2021. "Vector Current Measurement Using Doppler Scatterometry with Optimally Selected Observation Azimuths" Remote Sensing 13, no. 21: 4263. https://doi.org/10.3390/rs13214263