# Characterizing the Effect of Ocean Surface Currents on Advanced Scatterometer (ASCAT) Winds Using Open Ocean Moored Buoy Data

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## Abstract

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## 1. Introduction

## 2. Data and Methods

## 3. Results

#### 3.1. Effect of Surface Current on Satellite Wind

#### 3.2. Correction of Scatterometer-Derived Ocean Surface Wind Speed

## 4. Discussions

## 5. Conclusions

## Author Contributions

## Funding

## Data Availability Statement

## Acknowledgments

## Conflicts of Interest

## References

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**Figure 1.**(

**a**) The spatial distributions of the 40 moored buoys. (

**b**) Timeline of hourly wind vector and current vector observations from these operational buoys. Distinct colors are utilized to denote moored buoy data acquired from various projects or organizations.

**Figure 2.**(

**a**) The number of data triplets that the ASCAT L2 wind vector matched with the moored buoy’s wind vector and current vector. (

**b**) is the same as (

**a**), but for the ASCAT L3 wind vector.

**Figure 3.**(

**a**) Multi-year averaged ocean surface current speed from 2007 to 2021. The gray arrows indicate the average current direction. (

**b**) The probability density function (PDF) of the magnitude of the current speed, zonal component |u|, and meridional component |v|. (

**c**) The PDF of the current direction and the angle between the current vector and wind vector.

**Figure 4.**Comparisons of (

**a**) the wind speed (WSPD), (

**b**) the zonal and (

**c**) meridional wind components between the buoy-based earth-relative observations and the collocated ASCAT L2 data. (

**d**–

**f**) are the same as (

**a**–

**c**) but for the ASCAT L3 products. The color of each dot represents the density of the data. The number (n) of data pairs in each panel is noted in the title.

**Figure 5.**The relationship between the ASCAT L2 wind bias and ocean surface velocity. The panels in each column represent differing buoys with all buoys on the left. The panels in each row represent the differing variables, with the scalar wind speed bias on the top. The bin-averaged wind bias with error bars as a function of the surface current is shown in each panel. The black dashed line provides the result from a linear regression fit, and the gray dashed line indicates a linear relationship with a slope of unity. The regression equation and the correlation coefficient (R) are noted in each panel. The number of data triplets and the distribution of the surface current speed are depicted in red shades.

**Figure 6.**The same as Figure 5 but for the ASCAT L3 wind product.

**Figure 7.**(

**a**–

**c**) The correlation coefficients and (

**d**–

**f**) the slopes of the linear regression equation between the ASCAT L2 wind bias and the surface current velocity. (

**a**,

**d**) are for the scalar wind speed bias and projected current speed. (

**b**,

**e**) represent the zonal wind speed bias and surface velocity, while (

**c**,

**f**) correspond to the meridional component. Stations where the linear correlation does not pass the significance test at a 95% confidence level are labeled with gray triangles.

**Figure 8.**The same as Figure 7 but for the ASCAT L3 wind product.

**Figure 9.**Comparison of the ASCAT scalar wind speed and the buoy wind speed. The ASCAT wind speeds in (

**a**,

**c**) are uncorrected, while they have been corrected with surface current measured via moored buoys in (

**b**,

**d**). (

**a**–

**d**) represent the results for the ASCAT L2 and L3 wind products, respectively. The color of the points indicates the projection of the ocean surface current onto the direction of the buoy-observed wind. The number (n) of data triplets in each panel is noted in the title.

**Figure 10.**Comparisons of the zonal current $u$ between the buoy observations and CMEMS reprocessing. Each subfigure represents data from different buoy stations, with the coordinates of each buoy indicated in the subfigure’s title. The color of each dot represents the density of the data. The number (n) of data pairs and the correlation coefficient (R) are noted in the top left corner of each panel. The units of bias and RMSEs are in meters per second (m/s).

**Figure 12.**The same as Figure 9, but the reprocessed current is utilized for the correction of the ASCAT winds.

**Figure 13.**The root-mean-square error of the ASCAT wind speed before and after correction using the ocean surface current. The corresponding percentages indicate the extent of the reduction in RMSE achieved.

**Table 1.**The multi-year averaged coordinates of each buoy, along with the sensor types and deployment depths for ocean current measurements.

Buoy ID | Longitude | Latitude | Depth | Sensor Type |
---|---|---|---|---|

KEO | 144.6°E | 32.4°N | 5 m, 6 m, 8 m, 11.5 m, 15 m, and 15.6 m at different deployment durations | Sontek, TRDI Doppler volume sampler and Nortek Aquadopp current meter at different deployment durations |

Papa | 144.8°W | 50.1°N | 5 m, 6 m, and 15 m at different deployment durations | Sontek, TRDI Doppler Volume Sampler and Nortek Aquadopp Current Meter at different deployment durations |

OOI-104233 | 89.2°W | 54.4°S | 12 m | Single-point velocity meter |

OOI-104007 | 42.4°W | 42.9°S | 12 m | Single-point velocity meter |

WHOI-WHOTS | 157.9°W | 22.7°N | 10 m | Vector measuring current meter |

WHOI-Stratus | 85.3°W | 20.2°S | 7 m, 10 m, 13 m 15 m, and 20 m at different deployment durations | Aanderaa ADCM, NORTEK ADCM, and Aanderaa RCM11 at different deployment durations |

WHOI-NTAS | 51.0°W | 14.8°N | 5.7 m, 6 m, 12 m, and 13 m at different deployment durations | Aquadopp current meter, NORTEK ADCM, and NORTEK current meter at different deployment durations |

RAMA | 65.1°E | 15.1°N | 12 m | Sontek |

67.0°E | 8.1°S | |||

67.2°E | 12.2°S | |||

67.2°E | 4.0°S | |||

80.4°E | 11.9°S | |||

80.5°E | 4.0°S | |||

80.5°E | 8.0°S | |||

89.0°E | 8.0°N | |||

89.1°E | 12.0°N | |||

95.0°E | 5.0°S | 10 m | ||

95.1°E | 8.1°S | |||

TAO/TRITON | 136.6°E | 7.8°N | 10 m | Sontek |

137.3°E | 4.9°N | |||

138.1°E | 2.0°N | |||

147.0°E | 0.0°N | |||

147.0°E | 2.0°N | |||

147.0°E | 5.0°N | |||

156.0°E | 0.0°N | |||

156.0°E | 2.0°N | |||

156.0°E | 2.0°S | |||

156.0°E | 5.0°N | |||

156.0°E | 5.0°S | |||

156.0°E | 8.0°N | |||

PIRATA | 38.0°W | 15.0°N | 12 m | Sontek |

38.0°W | 4.1°N | |||

37.9°W | 20.0°N | |||

35.0°W | 0.0°N | |||

23.1°W | 20.5°N | |||

23.0°W | 0.0°N | |||

23.0°W | 11.5°N | |||

23.0°W | 4.0°N | |||

10.0°W | 9.9°S | |||

10.0°W | 6.0°S |

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**MDPI and ACS Style**

Cheng, T.; Chen, Z.; Li, J.; Xu, Q.; Yang, H.
Characterizing the Effect of Ocean Surface Currents on Advanced Scatterometer (ASCAT) Winds Using Open Ocean Moored Buoy Data. *Remote Sens.* **2023**, *15*, 4630.
https://doi.org/10.3390/rs15184630

**AMA Style**

Cheng T, Chen Z, Li J, Xu Q, Yang H.
Characterizing the Effect of Ocean Surface Currents on Advanced Scatterometer (ASCAT) Winds Using Open Ocean Moored Buoy Data. *Remote Sensing*. 2023; 15(18):4630.
https://doi.org/10.3390/rs15184630

**Chicago/Turabian Style**

Cheng, Tianyi, Zhaohui Chen, Jingkai Li, Qing Xu, and Haiyuan Yang.
2023. "Characterizing the Effect of Ocean Surface Currents on Advanced Scatterometer (ASCAT) Winds Using Open Ocean Moored Buoy Data" *Remote Sensing* 15, no. 18: 4630.
https://doi.org/10.3390/rs15184630