臺灣博碩士論文加值系統

摘要

本研究利用超高解析輻射儀(AVHRR)擷取1996~2003年海洋表面水溫衛星影像及現場船測水溫資料配合統計分析進行冬季臺灣海峽海表溫變動特性之解析。研究期間共有961筆配對資料組(match up data set)，而所得有效覆蓋率大於85%的無雲影像資料為全部的2.23%；現場實測海洋表面水溫範圍在10.5 ℃~30.8℃。經驗正MCSST及NLSST推算所得水溫值與現場實際水溫值之結果呈現線性相關，相關係數分別為0.985與0.98，而二者的偏差（biases）分別為0.01℃與0.26℃，方均根誤差（root mean square deviation）分別為0.64℃與0.80℃，這表示利用AVHRR估測臺灣周邊水域之MCSST及NLSST海洋表面水溫值是可信的。
81張週平均的無雲影像經過EOF分析後，海洋表面水溫空間平均值之時序列趨勢呈現出類似於季節性的能量變動，其平均水溫約為20℃；空間模式的變異明顯高於時間模式，其空間第一個模式（85.7％）顯示於彰雲隆起（CYR）附近有一道持續性的溫度鋒面，將東北方的大陸沿岸冷水（<19 ℃）與西南方的暖水（>22 ℃）明顯地區隔開來；該鋒面區的最大溫度梯度與鹽度梯度分別為0.11℃/km與0.048 psu/km，而第二及第三空間模式的解釋變異量則明顯降低，分別為3.13%與1.92%。
文中我們也嘗試建立一個冷水指標來探討大陸沿岸水、南中國海暖流水與黑潮反流三者間的相對勢力強弱關係。當黑潮支流愈北向臺灣海峽入侵則冷水指標的C值愈大，經廻歸後二者呈現線性關係，其相關係數為0.71，其中C值更與大於20 ℃之暖水覆蓋面積達到95%之顯著水準。因此，20 ℃等溫線可做為冬季臺灣海峽中大陸沿岸流與黑潮支流間之邊界。

關鍵字：海洋表面水溫、驗正、經驗正交函數、超高解析輻射儀、臺灣海峽、冷水指標、黑潮反流。

Abstract

Satellite-sensed Advanced Very High Resolution Radiometer (AVHRR) sea surface temperature (SST) data over eight winters (1996-2003) and shipboard measurement during winter 2002 were used to analyze the winter SST patterns of variability in the middle of Taiwan Strait. These satellite-derived SST images conducted by MCSST and NLSST algorithm in the waters around Taiwan were firstly validated from a match-up data set of 961 pairs, which included the in situ SSTs and concurrent AVHRR measurements for the period of 1998 to 2002. Availability of cloud-free images, which had more than 85% of cloud-free area in their coverage, was about 2.23 % of the whole AVHRR senses in the study period. The range of in situ SSTs was from 10.5℃ to 30.8 ℃. The satellite derived-SSTs through the MCSST and NLSST algorithms with the NOAA-published coefficients are linearly related to the in situ SSTs with correlation coefficients of 0.985 and 0.98, respectively. The MCSSTs and NLSSTs have small biases of 0.01 ℃ and 0.26 ℃ with the root mean square deviation 0.64 ℃ and 0.80 ℃, respectively, which conclude that the AVHRR-based MCSSTs and NLSSTs have high accuracy in the waters around Taiwan.
Empirical orthogonal function (EOF) analysis of the spatial and temporal variance for 81 nearly cloud-free quarter monthly images was performed. The time series of spatial mean SST was like a non-linear mode associated with the seasonal thermal variation, having an average value about 20 ℃. The EOF analysis shows that the variance of oceanic feature was more significant in space than in time. The first mode (85.7%) of the spatial variance shows a persistent front near the Chang-Yuen Ridge in the middle of Taiwan Strait, which separates warmer surface water (>22 ℃) to the southeast from the colder waters (<19 ℃) off Mainland China to the northwest. The maximum temperature and salinity gradient at Chang-Yuen Ridge were found about 0.11℃/km and 0.048 psu/km, respectively. The second and third spatial variance modes are extremely low energy about 3.13% and 1.92 %, respectively.
The EOF’s signal and field observation revealed that the heating exchange, balance and its strength (i.e. coolness index) of cold water to warm water were temporally shifted in winter. From these images, we also constructed an overall coolness index, which revealed the relative strength of Mainland China Coastal Current in relation to the interaction of the South China Sea Warm Current and Kuroshio Counter Current.
In other words, the higher the coolness index is, the larger the coverage area of KBC northward intruding into Taiwan Strait. Among them, this regression line with the higher coefficient 0.71 was only reach to the significant level 95% at the temperature range larger than 20 ℃. It also suggested that the isotherm line of sea surface temperature 20 ℃ might be served as a winter thermal front boundary index of MCCC and KBC in Taiwan Strait.



Keyword: Sea surface temperature (SST), Validation, EOF, AVHRR, Taiwan Strait, Coolness index, Kuroshio Counter Current.

Index

Table contents...............................................................Ⅳ
Figure contents……………………………………….Ⅴ
Abstract (in Chinese)...................................................Ⅷ
Abstract.........................................................................Ⅹ
Chapter 1: Introduction……………………………….1
1.1. The origin of this study…………….………...….1
1.2. Motivation.............................................................2
1.3. Thesis structure.....................................................3
Chapter 2: Validation of the satellite-derived SSTs in the waters around Taiwan.........................4
2.1. Overview of concept............................................4
2.2. Data and method………………………………...6
2.2.1. Retrieval of Satellite-derived SSTs and in situ measurements………………………..6
2.2.2. Match up dataset…………………………8
2.3. Result and discussions…………………………..8
2.3.1. Cloud-free image availability…………….8
2.3.2. Characteristics of in situ SSTs in the study area………………...……………………9
2.3.3. Comparison of the satellite-derived and in situ SSTs……………………………......10
2.4. Discussion……………………………...………11
Chapter3: Winter Sea surface temperature variability in the middle of Taiwan Strait as derived from satellite and shipboard data……....14
3.1. Geography and hydrographic features of Taiwan Strait…...………………………………………14
3.2. Data and methods…………..…………………..15
3.2.1. Satellite SST images and in situ observation…………………………...15
3.2.2. EOF analysis……………………………17
3.2.3. Coolness index………………………….19
3.3. Results………………………………………….20
3.3.1. Hydrography……………………………20
3.3.2. Sea surface temperature images………...21
3.3.3. Spatial and temporal variance of SST…..23
3.3.4. Coolness index variation………………..25
3.4. Discussion………………………………...……25
Chapter 4: Conclusion……………………………….31
4.1. Summery……………………………………….31
4.2. Prospect of future study………………………..32
Acknowledgments……………………………………34
References…………………………………………….35


Table contents

Table 1 Coefficients of MCSST and NLSST algorithms……………..43
Table 2 Monthly distribution of match-up data created in the study period………………………………………………………………44
Table 3 Maximum and minimum in situ SSTs (℃) and observation number for each subdivision area. Yearly mean and standard deviation of the in situ SSTs are also shown………………………45
Table 4 The root mean square deviation (RMSD) and bias of the difference between the in situ SSTs and satellite derived-MCSST and NLSST……………………………………………………..….46
Table 5 The information of cruises from each research vessel during the study period………………………………………………..…..47
Table 6 Lists of the sampling errors in the estimation of the first 5th EOFs in this study……………………………………………..…..48
Table 7 Lists of the Regression lines for Coolness Index (C, ) and Warm water area (WWA, 1000 km2) at different temperature range in the middle of Taiwan Strait…………………………...….49






Figure contents

Figure 1. The component of HRPT remote sensing system…………..50
Figure 2. The instantaneous views of ocean front in the waters around Taiwan from satellite remote sensing images, the red point indicates Taiwan…………………………………………………...51
Figure 3. Flowchart of this study……………………………………..52
Figure 4. Spatial distribution of the field CTD observation stations used in this study. A~D: four subdivisions in the study area, i.e., A: the Kuroshio region, B the southern East China Sea, C: the Taiwan Strait and D: the northern South China Sea. Different symbols (×、＋、◊、○) of CTD stations are used for the subdivisions. The solid line indicated the isopleth line of 200 meter depth……………………..53
Figure 5. Monthly number of passes and cloud-free images for the
study area…………………………………………………………..54
Figure 6. Frequency distribution of the in situ SSTs in the study area...................................................................................................55
Figure 7. Seasonal mean SST (A) and standard deviations (B) for each subdivision area during the period of January 1998 to December 2002………………………………………………………………..56
Figure 8. Relationship between the MCSSTs and in situ SSTs……….57
Figure 9. Relationship between the NLSSTs and in situ SSTs………..58
Figure 10. The monthly time series of the difference between the NOAA MCSST values, NLSST values and in situ SSTs in different temperature range at different areas. Mark A~D represents the subdivision area shown in Figure 1……………………………….59
Figure 11. Histograms of MCSST (a) and NLSST (b) estimation errors. Classes ranging from –0.45℃ to 0.45℃ are shading…………….60
Figure 12. The difference between MCSST, NLSST and in situ SST versus T4-T5 in daytime (A) and nighttime (B)…………………...61
Figure 13. Survey area (dashed block), satellite infrared mean SST image and 152 time series water surface temperature measurement (solid circle) with CTD observation stations (red fluke) during the period of February 18 to 21, 2003. 82 mission data (open circle) of water surface temperature were also plotted in this figure. CYR and PH represent the location of Chang-Yuen Ridge and Peng-Hu islands, respectively………………………………………………………...62
Figure 14. Distribution of monthly NOAA series imageries from December to next March in 1996 to 2003…………………………63
Figure 15. Cool and warm regions used for calculating the coolness index as discussed in this study……………………………...…….64
Figure 16. Temperature and salinity curves during the period of February 18~21, 2003………………………………………………65
Figure 17. Comparison of AVHRR-derived mean MCSST with shipboard water surface temperature (in situ SST at 5 meter deep) along ship track in the survey area during the three observed period of February 18 to 21, 2003…………………………………………66
Figure 18. The vertical latitudinal distribution of temperature and salinity from south side (St01) to north side (St10) along about the longitude 120 E line in survey area………………………………..67
Figure 19. Statistics of temporal quarter monthly series of SST (upper panel: temporal quarter monthly mean; lower left panel: temporal mean; lower right panel: spatial mean)…………………………….68
Figure 20. The quarter monthly mean SST imageries derived by NOAA AVHRR data in the period of December to next March, 1995 to 2003………………………………………………………………..69
Figure 21. The first 25th EOF eigenvalues of quarter monthly satellite SST imagery data set for the temporal variance (solid curve with the triangle) and spatial variance (dashed curve with solid circle) in the winter of 1996 to 2003…………………………………………….70
Figure 22. The first three temporal and spatial amplitude images of EOF’s modes………………………………………………………71
Figure 23. The time-series temporal eigenvectors of first three spatial EOF’s modes………………………………………………………72
Figure 24. The annual winter coolness indices, warm water area and longitudinal shift distance (km) from 1996 to 2003……………….73
Figure 25. The relation of coolness index to the warm area (larger than 20 ) in the study…………………………………………………74
Figure 26. The negative relation of coolness index to the longitudinal shift distance of 20 isotherm line in northeast waters of Taiwan……………………………………………………………..75
Figure 27. The 20 isotherm line variation of the sea surface temperature images derived by NOAA-14 AVHRR in the western and northeastern waters of Taiwan during the period of January 2 to 6, 2000……………………………………………………………..76

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