Impact of Surface Soil Moisture Variations on Radar Altimetry Echoes at Ku and Ka Bands in Semi-Arid Areas
Abstract
:1. Introduction
2. Radar Altimetry Backscattering Modeling
2.1. Simulation of the Surface Backscattering Using the Kirchoff Model
2.1.1. Kirchoff Model of the Stationary Phase
2.1.2. Soil Dielectric Permittivity Estimates at Ku and Ka Bands
2.2. Altimeter Waveform Generation
2.2.1. Vectorial Polarimetric Backscattering
2.2.2. Monopulse Waveform
2.2.3. Averaged Waveform
3. Datasets
3.1. Radar Altimetry Data
3.2. ASTER DEM
4. Study Area
5. Results
5.1. Comparison between Simulated and Real Waveforms
5.2. Impact of Surface Soil Moisture on Altimetry Signal
6. Conclusions
- (1)
- a more realistic description of the open water areas taking into account the small undulations of the surface as in [43],
- (2)
- accurate values of the roughness parameters at Ku and Ka-bands and their spatio-temporal variations over the study sites,
- (3)
- DEM at higher spatial resolution and with a better accuracy, to obtain more accurate simulation results.
Acknowledgments
Author Contributions
Conflicts of Interest
Appendix A
Appendix B
- -
- the mean X position (noted as Xi further on),
- -
- the mean Y position (noted as Yi further on),
- -
- the mean Z position (noted as Zi further on),
- -
- the X axis component of the perpendicular vector (noted as Nx),
- -
- the Y axis component of the perpendicular vector (noted as Ny),
- -
- the Z axis component of the perpendicular vector (noted as Nz),
- -
- the nature of the elementary surface (−1 for water, 0 for ground is the default value),
- -
- the root mean square height hrms (noted as hi),
- -
- the surface correlation length (noted as li),
- -
- the triangle area (noted as Ai),
- -
- the surface complex dielectric permittivity (noted as εri),
Appendix C
Appendix D
Appendix E
ENVISAT RA-2 | SARAL AltiKa | |
---|---|---|
Mean satellite altitude (km) | 800 | 800 |
Velocity on orbit (km s−1) | 7.45 | 7.47 |
Apparent ground velocity (km s−1) | 6.62 | 6.64 |
Frequency bands | Ku (13.5 GHz), S (3.2 GHz) | Ka (35.5 GHz) |
Pulse duration (chirp sweep time) (µs) | 20 | 110 |
Effective pulse duration (ns) | 3.125 | 1 |
Bandwidth (MHz) | 320, 80, 20 (Ku) 160 (S) | 500 |
Pulse repetition frequency (Hz) | 1795 (Ku) 449 (S) | ~3800 |
Time between two pulses (T, µs) | 557 (Ku) 2230 (S) | ~263 |
Antenna parabola diameter (m) | 1.2 | 1 |
Footprint diameter (km) | ~18 | ~8 |
Antenna gain | 37 dB | 44 dB |
Emitted power (W) | 161 | 100 |
Distance between two consecutive measurements | 3.69 m | 1.66 m |
Void fraction (νa) | 0.36 | |
Sand ground component S | 60 | |
Clay ground component C | 20 | |
Soil bulk density (rb) | 1.69 | |
Alpha parameter | 0.65 | |
Temperature (°C) | 30 | |
Correlation length | 4.5 cm | |
Height rms (roughness) | 0.35 cm |
Ku Band | Ka Band | |
---|---|---|
kl (rad) | 12.72 | 33.46 |
l2 (10−3 m2) | 2.0 | 2.0 |
2.67sλ (10−3 m2) | 0.21 | 0.08 |
ks (rad) | 0.99 | 2.60 |
Appendix F
Simulation Site | ENVISAT RA-2 | SARAL/AltiKa | ||
---|---|---|---|---|
Empirical Gain (dB) | Timelag (ns) | Empirical Gain (dB) | Timelag (ns) | |
Site 1 | 343.42 | 0 | 339.03 | 33 |
Site 2 | 337.78 | −30 | 336.53 | 18 |
Site 3 | 341.76 | 35 | 336.02 | 158 |
Site 4 | 339.03 | 100 | 327.78 | 160 |
Site 5 | 335.44 | 425 | 330 | 164 |
Mean | 340.37 | n/a | 335.59 | n/a |
STD | 2.28 | n/a | 2.62 | n/a |
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ENVISAT RA-2 | SARAL AltiKa | |
---|---|---|
Mean satellite altitude (km) | 800 | 800 |
Velocity on orbit (km s−1) | 7.45 | 7.47 |
Apparent ground velocity (km s−1) | 6.62 | 6.64 |
Frequency bands | Ku (13.575 GHz), S (3.2 GHz) | Ka (35.75 GHz) |
Pulse duration (chirp sweep time) (µs) | 20 | 110 |
Effective pulse duration (ns) | 3.125 | 1 |
Bandwidth (MHz) | 320, 80, 20 (Ku) 160 (S) | 500 |
Pulse repetition frequency (Hz) | 1795 (Ku) 449 (S) | ~3800 |
Time between two pulses (T, en µs) | 557 (Ku) 2230 (S) | ~263 |
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Fatras, C.; Borderies, P.; Frappart, F.; Mougin, E.; Blumstein, D.; Niño, F. Impact of Surface Soil Moisture Variations on Radar Altimetry Echoes at Ku and Ka Bands in Semi-Arid Areas. Remote Sens. 2018, 10, 582. https://doi.org/10.3390/rs10040582
Fatras C, Borderies P, Frappart F, Mougin E, Blumstein D, Niño F. Impact of Surface Soil Moisture Variations on Radar Altimetry Echoes at Ku and Ka Bands in Semi-Arid Areas. Remote Sensing. 2018; 10(4):582. https://doi.org/10.3390/rs10040582
Chicago/Turabian StyleFatras, Christophe, Pierre Borderies, Frédéric Frappart, Eric Mougin, Denis Blumstein, and Fernando Niño. 2018. "Impact of Surface Soil Moisture Variations on Radar Altimetry Echoes at Ku and Ka Bands in Semi-Arid Areas" Remote Sensing 10, no. 4: 582. https://doi.org/10.3390/rs10040582
APA StyleFatras, C., Borderies, P., Frappart, F., Mougin, E., Blumstein, D., & Niño, F. (2018). Impact of Surface Soil Moisture Variations on Radar Altimetry Echoes at Ku and Ka Bands in Semi-Arid Areas. Remote Sensing, 10(4), 582. https://doi.org/10.3390/rs10040582