Validation of Sentinel-1A SAR Coastal Wind Speeds Against Scanning LiDAR
<p>(<b>a</b>) Position of the RUNE experiment at approximately <math display="inline"> <semantics> <mrow> <mn>56</mn> <mo>.</mo> <msup> <mn>50</mn> <mo>∘</mo> </msup> </mrow> </semantics> </math>N, <math display="inline"> <semantics> <mrow> <mn>8</mn> <mo>.</mo> <msup> <mn>12</mn> <mo>∘</mo> </msup> </mrow> </semantics> </math>E in the Norther Sea on the West Coast of Denmark. Coordinates of the map are in UTM32 WGS84. The transect for the reconstructed LiDAR wind speeds is shown as a dotted line. Positions of the measurement devices are: H: Tall meteorological mast at Høvsøre, DD1 and DD2: scanning LiDARs performing dual Doppler scans (example of coordinated measurements on the transect in dashed lines), SC: scanning LiDAR performing sector scans and profiling LiDAR P. (<b>b</b>) Picture of the deployed scanning LiDAR (SC) and profiling LiDAR (P) for the RUNE experiment. Photo by Mike Courtney.</p> "> Figure 2
<p>Sketch of the scan patterns of the transect in <a href="#remotesensing-09-00552-f001" class="html-fig">Figure 1</a> with the ocean on the left and the escarpment on the right. Indicated in black is the lowest sector scan (SC) and in dashed black the lowest elevation of the dual Doppler (DD) at 50 m above the sea. In gray the second elevation of SC and DD (only used for example cases in <a href="#sec3dot4-remotesensing-09-00552" class="html-sec">Section 3.4</a>). Horizontal scans as in cases 14 and 15 are not shown.</p> "> Figure 3
<p>Difference between SAR wind and scanning LiDAR wind measurements at 10 m. The distances on the transect are given in easting from the LiDAR system SC in <a href="#remotesensing-09-00552-f001" class="html-fig">Figure 1</a> located on the coast. 0 m is on the coast line and with decreasing easting, points are located further offshore. Individual cases are plotted in gray: (<b>a</b>) 11 cases with the dual Doppler and (<b>b</b>) 12 cases with sector scans. The thick black line is the mean over all cases with error bars indicating one standard deviation within each bin. The top plots show the number of available LiDAR measurements at each distance.</p> "> Figure 4
<p>Scatter plot for the average wind speed on the transect for SAR wind retrieved with CMOD5.N for (<b>a</b>) dual Doppler and (<b>b</b>) sector scan. Plot markers indicate the wind direction at the profiling LiDAR P, onshore for winds from the sea in the west between 180<math display="inline"> <semantics> <msup> <mrow/> <mo>∘</mo> </msup> </semantics> </math> and 360<math display="inline"> <semantics> <msup> <mrow/> <mo>∘</mo> </msup> </semantics> </math> and offshore for wind from the land between 0<math display="inline"> <semantics> <msup> <mrow/> <mo>∘</mo> </msup> </semantics> </math> and 180<math display="inline"> <semantics> <msup> <mrow/> <mo>∘</mo> </msup> </semantics> </math> . Numbers indicate the case numbers in <a href="#remotesensing-09-00552-t002" class="html-table">Table 2</a> and <a href="#remotesensing-09-00552-t003" class="html-table">Table 3</a>.</p> "> Figure 5
<p>Mean 10 m wind speed for all cases from dual Doppler and sector scans and the mean of the collocated SAR wind speeds.</p> "> Figure 6
<p>Relative wind speed nodimensionalized with the wind speed at −3000 m for from the LiDAR and the SAR for (<b>a</b>) the dual Doppler and (<b>b</b>) the sector scans.</p> "> Figure 7
<p>Wind speeds extrapolated to 10 m from the dual Doppler (DD) and sector scan (SC) and SAR wind speeds. Additionally, to the extrapolation from the lowest level, as used for <a href="#remotesensing-09-00552-f003" class="html-fig">Figure 3</a> to <a href="#remotesensing-09-00552-f006" class="html-fig">Figure 6</a>, extrapolations from the 100 m level for the dual Doppler and the second lowest level of the sector scans are included (see <a href="#remotesensing-09-00552-f002" class="html-fig">Figure 2</a>). Cases 6, 10 and 11 from <a href="#remotesensing-09-00552-t002" class="html-table">Table 2</a> and <a href="#remotesensing-09-00552-t003" class="html-table">Table 3</a> are shown. SAR winds are in thick black and scanning LiDAR measurements in thin gray. For case 6, the thick gray line shows the SAR wind retrieval with an adjusted normalised radar cross section, in order to remove discontinuities from <a href="#remotesensing-09-00552-f008" class="html-fig">Figure 8</a>.</p> "> Figure 8
<p>Extra Wide Swath mode SAR wind map for case 6. Wind direction inputs are taken from a global GFS model with 0.25<math display="inline"> <semantics> <msup> <mrow/> <mo>∘</mo> </msup> </semantics> </math> resolution and 6 h time steps rather than a fixed wind direction. The black star indicates the position of the RUNE experiment and the entire campaign area lies in the first subswath furthest East.</p> ">
Abstract
:1. Introduction
2. Materials and Methods
2.1. Sentinel-1A SAR
Wind Direction Input for SAR Wind Retrieval
2.2. LiDAR Measurements
2.2.1. Scanning LiDARs
2.2.2. Profiling LiDAR
2.3. Meteorological Mast
2.4. Available Cases
2.5. Method for Comparing SAR and LiDAR Data
2.5.1. Vertical Displacement
2.5.2. Temporal and Horizontal Displacement
3. Results
3.1. Differences over the Transect
3.2. Spatially Averaged Wind Speed
3.3. Ensemble Averaged Wind Speed
3.4. Example Cases
4. Discussion
5. Conclusions
Acknowledgments
Author Contributions
Conflicts of Interest
Abbreviations
SAR | Synthetic Aperture Radar |
LiDAR | Light Detection and Ranging |
GMF | Geophysical Model Function |
CMOD | C-band model |
CMOD5.N | C-band model 5.N |
RMSE | Root Mean Square Error |
RUNE | Reducing uncertainty of near-shore wind resource estimates using onshore LiDAR |
SAROPS | SAR Ocean Products System |
DD | Dual Doppler |
SC | Sector Scan |
STD | Standard deviation |
DTU | Technical University of Denmark |
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Reference | Samples | Location | RMSE () | Sensor |
---|---|---|---|---|
Hasager et al. [9] | 149 to 197 | Denmark/The Netherlands | 1.27 to 1.65 | Envisat |
Chang et al. [10] | 552 | South Chinese Sea | 2.09 | Envisat |
Takeyama et al. [11] | 42 | Japan | 0.75 to 2.24 | Envisat |
Chang et al. [12] | 522 | East Chinese Sea | 1.99 | Envisat |
Takeyama et al. [13] | 33 to 73 | Japan | 0.64 to 2.34 | Envisat |
Hasager et al. [14] | 875 | Baltic Sea | 1.17 | Envisat |
Christiansen et al. [15] | 91 | Denmark | 1.1 to 1.8 | ERS2 |
Hasager et al. [16] | 61 | Denmark | 0.9 to 1.14 | ERS2 |
Case | Date | Time | Pol. | Mode | Orbit | |
---|---|---|---|---|---|---|
1 | 7 December 2015 | 17:09 | HH | EW | D | 37 |
2 | 9 December 2015 | 05:40 | VV | EW | A | 43 |
3 | 12 December 2015 | 17:17 | VV | IW | D | 44 |
4 | 14 December 2015 | 05:48 | HH | EW | A | 36 |
5 | 26 December 2015 | 05:48 | HH | IW | A | 36 |
6 | 31 December 2015 | 05:56 | HH | IW | D | 27 |
7 | 31 December 2015 | 17:09 | HH | IW | D | 37 |
8 | 12 January 2016 | 17:09 | HH | EW | A | 37 |
9 | 19 January 2016 | 05:48 | VV | EW | A | 36 |
10 | 26 January 2016 | 05:40 | VV | EW | D | 43 |
11 | 29 January 2016 | 17:17 | HH | EW | D | 44 |
12 | 5 February 2016 | 17:09 | HH | EW | D | 37 |
13 | 12 February 2016 | 05:48 | VV | IW | A | 36 |
14 | 17 February 2016 | 17:09 | HH | IW | D | 37 |
15 | 29 February 2016 | 05:57 | HH | EW | A | 27 |
Case | DD | SC | m | (40 m) (m) | Stab Class | |
---|---|---|---|---|---|---|
1 | x | 7.5 | 148.5 | 40 | very stable | |
2 | x | 13.6 | 277 | 1320 | neutral | |
3 | x | 5.2 | 234 | 123 | stable | |
4 | x | 4.7 | H:167 | 50 | very stable | |
5 | x | x | 5.0 | 80 | 31 | very stable |
6 | x | x | 13.0 | 149 | −1480 | neutral |
7 | x | 10.0 | 205 | 46 | very stable | |
8 | x | x | 10.5 | 56 | 596.5 | neutral |
9 | x | x | 7.3 | 347 | - | - |
10 | x | x | 11.5 | 264 | 175 | stable |
11 | x | x | 19.0 | 250 | 1001 | neutral |
12 | x | x | 10.0 | 213 | 53 | very stable |
13 | x | x | 6.4 | 40 | 39 | very stable |
14 | x | 8.3 | 141 | 41 | very stable | |
15 | x | 4 | 133 | 43 | very stable |
- | 1 km | 1.5 km | 2 km | 3 km | |
---|---|---|---|---|---|
Cells (-) | 1 | 2 | 3 | 4 | 6 |
(ms) | - | −0.01 | −0.02 | −0.03 | −0.04 |
(ms) | - | 0.18 | 0.21 | 0.24 | 0.28 |
RMSE () | 1.53 | 1.45 | 1.41 | 1.42 | 1.43 |
Mean Bias (ms) | Median STD (ms) | Min STD (ms) | Max STD () | |
---|---|---|---|---|
DD | −0.57 | 1.30 | 1.07 | 1.62 |
SC | −0.17 | 1.47 | 1.17 | 1.98 |
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Ahsbahs, T.; Badger, M.; Karagali, I.; Larsén, X.G. Validation of Sentinel-1A SAR Coastal Wind Speeds Against Scanning LiDAR. Remote Sens. 2017, 9, 552. https://doi.org/10.3390/rs9060552
Ahsbahs T, Badger M, Karagali I, Larsén XG. Validation of Sentinel-1A SAR Coastal Wind Speeds Against Scanning LiDAR. Remote Sensing. 2017; 9(6):552. https://doi.org/10.3390/rs9060552
Chicago/Turabian StyleAhsbahs, Tobias, Merete Badger, Ioanna Karagali, and Xiaoli Guo Larsén. 2017. "Validation of Sentinel-1A SAR Coastal Wind Speeds Against Scanning LiDAR" Remote Sensing 9, no. 6: 552. https://doi.org/10.3390/rs9060552