Journal of Tropical Oceanography >
A study of data processing and quality assessment of the eddy convariance system off Yongxing Island
Received date: 2016-11-25
Request revised date: 2017-03-06
Online published: 2017-07-26
Supported by
Station Network Construction Project, Chinese Academy of Sciences-Xisha Marine Observatory (KZCX2-YW-Y202)
Chinese Academy of Sciences Key Technology Talent Program-2016
Copyright
This study was based on the raw eddy-covariance (EC) data measured in February 2016 from the observation tower on Yongxing Island. EddyPro software was used for data post-processing, and the influence on flux calculation was quantitatively analyzed before and after each processing step. Furthermore, flux data quality classification, footprint analysis and comparison with calculated results using easyflux_dl real time programme were conducted. The results showed that despiking, coordinate rotation, frequency response correction and density correction all influenced the flux calculation result to different degrees. The influences of coordinate rotation on momentum flux, latent heat flux and carbon dioxide flux were evident, which revealed increases of 11.28%, 7.36% and 18.53%, respectively. The density correction had a significant effect on the carbon dioxide flux calculation, which was reduced by 7.87% after density correction. Comprehensive quality evaluation results revealed that the ratios of high quality data (grades 1~3) of momentum flux, sensible heat flux, latent heat flux, and carbon dioxide flux were 90.29%, 90.22%, 88.46%, and 85.41%, respectively. Footprint analysis showed that 72.04% source area of the flux was scattered in the first interesting area (10~80°, the underlying surface is the ocean surface with an average water depth of more than 10 m). Comparison of flux calculation results between EddyPro and EasyFlux showed that the two flux time series were fundamentally consistent; the results obtained by EddyPro were smaller but more reliable and accurate due to more strict despiking adopted to get rid of outliers’ impacts.
ZHOU Fenghua , ZHANG Rongwang , SHI Rui , HE Yunkai , CHEN Ju , WANG Dongxiao , XIE Qiang . A study of data processing and quality assessment of the eddy convariance system off Yongxing Island[J]. Journal of Tropical Oceanography, 2017 , 36(4) : 48 -59 . DOI: 10.11978/2016124
Fig. 1 Schematic diagram of the system integration on the observation tower图1 永兴岛观测塔系统集成框架 |
Tab. 1 List of sensors mounted on the observation tower表1 永兴岛气象观测塔设备 |
设备(型号) | 采样频率/Hz | 数据表间隔/min | 观测项目 | 安装高度/m |
---|---|---|---|---|
风速传感器(Young 05106) | 1 | 1、10、30 | 4层风速风向 | 5、10、15、20 |
温湿度传感器(Vaisala HMP155A) Vaisala HMP155A | 1 | 1、10、30 | 4层温湿度 | 5、10、15、20 |
四分量辐射仪(Hukseflux NR01) | 1 | 1、10、30 | 向上、向下; 短波和长波辐射 | 8 |
海表红外温度计(CSI SI-111) | 1 | 1、10、30 | 下垫面海表温度 | 10 |
涡动相关仪(CSAT3 & EC150) | 10 | 30 | 感热、潜热、动量、二氧化碳通量 | 12 |
Fig. 2 Yongxing Island observation tower and the instruments installed图2 西沙永兴岛综合观测塔及仪器安装 红色倒三角为观测塔位置 |
Fig. 3 Flow chart of turbulence data processing and quality assessment图3 湍流数据处理与质量评价流程 |
Fig. 4 Distribution of wind speed and wind direction in February 2016图4 永兴岛2016年2月份风速风向分布 WS指风速, 单位: m·s-1 |
Fig. 5 Comparison of flux calculated before and after despiking图5 野点剔除前后通量变化 |
Fig. 6 Distribution of wind speed and wind direction during day and night in February 2016图6 2016年2月份白天和夜间风速和风向分布 WS指风速, 单位: m·s-1 |
Fig. 7 Comparison of flux calculated before and after coordinate rotation图7 坐标旋转前后通量变化 |
Fig. 8 Comparison of fluxes calculated before and after frequency correction图8 WPL密度补偿前后通量变化 |
Fig. 9 Directional distributions of the IST at the site for fluxes in Feb 2016图9 湍流发展的平稳性检验 a. 动量通量; b. 感热通量; c. 潜热通量; d. 二氧化碳通量 |
Tab. 2 Steady test grading criteria表2 湍流平稳性检验分级标准(Moncrieff et al, 1997) |
质量等级 | IST/% |
---|---|
1 | 0~15 |
2 | 16~30 |
3 | 31~50 |
4 | 51~75 |
5 | 76~100 |
6 | 101~250 |
7 | 251~500 |
8 | 501~1000 |
9 | >1000 |
Tab. 3 Developed turbulence test grading criteria表3 湍流充分发展检验分级标准(Moncrieff et al, 1997) |
质量等级 | ITC/% |
---|---|
1 | 0~15 |
2 | 16~30 |
3 | 31~50 |
4 | 51~75 |
5 | 76~100 |
6 | 101~250 |
7 | 251~500 |
8 | 501~1000 |
9 | >1000 |
Fig. 10 Quality grading of steady test图10 湍流平稳性检验分级结果 |
Tab. 4 Overall flux data quality grading criteria表4 通量总体质量分级标准 |
等级 | IST/% | ITC/% |
---|---|---|
1 | 0~15 | 0~30 |
2 | 16~30 | 0~30 |
3 | 0~30 | 31~75 |
4 | 31~75 | 0~30 |
5 | 0~75 | 31~100 |
6 | 76~100 | 0~100 |
7 | 0~250 | 0~250 |
8 | 0~1000 | 0~1000 |
9 | >1000 | >1000 |
Fig. 11 Directional distributions of the integral turbulence characteristics (ITC) at the study site for unstable, neutral and stable conditions图11 垂直风速的湍流充分发展检验在不同稳定层结下随风向分布图 a. 不稳定层结; b. 中性层结; c. 稳定层结 |
Fig. 12 Quality grading of ITC according to wind direction图12 湍流发展充分检验随风向分级结果 |
Fig. 13 Overall flux data quality grading for momentum, sensible heat, latent heat, and CO2 flux图13 湍流通量总体质量评价 |
Fig. 14 Footprint source area distribution in Feb图14 观测站2月份通量源区图 |
Fig. 15 Comparison of the fluxes calculated by EddyPro and EasyFlux_DL in Feb 2016图15 EddyPro与EasyFlux_DL通量结果时间序列 |
Fig. 16 Comparison of the fluxes calculated by EddyPro and Easyflux图16 EddyPro与EasyFlux通量结果比较 |
The authors have declared that no competing interests exist.
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