1. School of Earth Sciences, Zhejiang University, Hangzhou 310058, China 2. Ocean Academy, Zhejiang University, Zhoushan 316000, China 3. Key Laboratory of Zhejiang Ocean Observation-Imaging Testbed of Zhejiang Province, Zhoushan 316000, China 4. China Aero Geophysical Survey and Remote Sensing Center for Natural Resources, Beijing 100083, China
The sea area around Daijin Island of Huangmao Sea in the Pearl Estuary, China is the habitat of Chinese white dolphins. Compact airborne spectrographic imager (CASI) image was employed to observe the suspended sediment concentration (SSC), and a single band inversion model for the CASI and moderate-resolution imaging spectroradiometer (MODIS) was established based on the in-situ spectral measurement, in order to assess the sea water quality in this area. The accuracy of inversion SSC was assessed by MODIS with in-situ SSC data. Results show that single-band exponential model based on CASI data performs well in inversing the suspended sediment concentration in the experimental sea area with the relative error of 11.16%, and of 15.18% for MODIS. The suspended sediment concentration in the study area ranges from 0.48 to 12.15 mg/L, and the direct ecological impact to the dolphin reserve should be neglected. Combined with the observation from MODIS image of suspended sediment in the Pearl Estuary, the land-based input from the west coast of Huangmao Sea is identified as the main material source, meanwhile, there is obvious branching phenomena when the terrestrial sediments are transported from the Huangmao Sea to the outside of the estuary. The main axis of runoff is transported from northwest to southeast in the estuary, while the coastal current is transported from northeast to southwest along Dajin Island. As a result, area with low suspended sediment and high transparency forms in the north of Dajin Island, which is suitable for the thriving of dolphin.
Guo-rong HUANG,Xiao-yu ZHANG,Ya-chao HAN,Jia-xing CHEN,Yong-jun ZHANG. Observation of suspended sediment in sea area around Dajin Island based on multi-source remote sensing data. Journal of ZheJiang University (Engineering Science), 2020, 54(5): 985-995.
Fig.1True color synthesis of CASI data in study area
Fig.2Distribution of ground control points and checkpoint route of CASI
Fig.3Noise of water body in study area
Fig.4Fast view of MODIS image used in study with Dajin Island and surrounding waters marked by box
Fig.5In situ water sampling and spectral measurement locations in sea area around Dajin Island
站位
经度
纬度
ρB/（mg?L?1）
T1
113°4′26.34″
21°57′29.58″
10.07
T2
113°3′15.30″
21°54′19.38″
7.54
T3
113°2′24.24″
21°53′54.90″
8.74
T4
113°2′0.36″
21°53′40.5″
8.34
T5
113°4′18.84″
21°57′33.78″
9.54
T6
113°4′50.88″
21°56′49.68″
6.14
T7
113°5′13.20″
21°56′15.84″
1.77
T8
113°4′29.04″
21°55′41.64″
6.94
T9
113°5′41.04″
21°55′14.4″
1.87
T10
113°5′49.86″
21°54′43.14″
7.87
T11
113°2′33″
21°54′58.02″
10.94
T12
113°2′43.68″
21°54′27.78″
10.94
T13
113°2′50.1″
21°54′12.42″
11.14
T14
113°2′58.38″
21°53′59.92″
3.26
T15
113°3′8.7″
21°53′44.52″
11.74
T16
113°3′13.5″
21°53′28.02″
10.34
T17
113°3′21.12″
21°53′3.78″
18.74
T18
113°4′26.34″
21°57′29.58″
4.34
T19
113°3′15.30″
21°54′19.38″
2.14
T20
113°1′39.48″
21°51′10.14″
11.34
T21
113°1′34.62″
21°51′5.52″
3.54
T22
113°1′20.04″
21°51′1.62″
13.14
T23
113°1′13.62″
21°50′57.36″
3.54
T24
113°2′30.48″
21°54′4.92″
2.74
T25
113°2′14.82″
21°53′51.48″
7.34
T26
113°0′37.74″
21°50′55.98″
6.54
T27
113°0′1.26″
21°51′4.14″
3.74
T28
113°0′16.32″
21°51′2.7″
10.34
T29
112°59′56.4″
21°51′5.16″
8.74
T30
112°59′52.32″
21°51′18.9″
2.74
T31
112°59′56.28″
21°51′33.9″
2.34
T32
112°59′55.62″
21°51′44.04″
10.54
T33
112°59′57.12″
21°51′53.46″
8.14
T34
112°59′58.2″
21°51′54.78″
9.74
T35
113°0′0.6″
21°52′2.34″
8.74
T36
113°0′0.72″
21°52′10.38″
7.54
T37
113°0′4.62″
21°52′19.8″
9.94
Tab.2Longitude and latitude of stations and measured suspended sediment mass concentration
Fig.6Spectral curves measured in water body around Dajin Island before and after denoising（taking T22 station as an example）
Fig.7Denoised spectral curves measured in water body around Dajin Island
Fig.8Correlation coefficient between measured suspended sediment mass concentration and remote sensing reflectance
Fig.9Comparison of different SSC inversion models based on single band reflectance of CASI
Fig.10Comparison of different SSC inversion models based on CASI bands ratio
站位号
ρB/(mg·L?1)
e/%
实测
反演
*P<0.01
T14
3.26
2.51
23.02
T17
18.74
16.41
12.43
T21
3.54
2.90
18.15
T23
3.54
3.30
6.68
T24
2.74
2.73
0.31
T27
3.74
3.29
11.90
T30
2.74
2.57
6.03
T31
2.34
2.09
10.73
Tab.3Error analysis of SSC obtained by single band inversion model
站位号
ρB/(mg·L?1)
e/%
实测
反演
*P<0.01
T14
3.26
2.94
9.67
T17
18.74
14.36
23.35
T21
3.54
2.50
29.30
T23
3.54
2.98
15.81
T24
2.74
2.40
12.27
T27
3.74
3.43
8.17
T30
2.74
2.62
4.55
T31
2.34
1.59
32.05
Tab.4Error analysis of SSC obtained by bands ratio inversion model
Fig.11Inversion of SSC from CASI data in Dajin Island
Fig.12Inversion of SSC from MODIS data in Pearl River Estuary with range of CASI image marked by box
站位号
ρB/(mg·L?1)
e/%
实测
反演
T1
10.07
8.81
12.48
T2
7.54
6.43
14.68
T3
8.74
7.84
10.31
T4
8.34
7.07
15.27
T5
9.54
8.80
7.76
T6
6.14
5.04
17.98
T7
1.77
1.43
19.48
T8
6.94
5.91
14.86
T9
1.87
1.56
16.61
T10
7.87
7.19
8.67
T11
10.94
9.58
12.45
T12
10.94
9.81
10.31
T14
3.26
2.34
28.12
T17
18.74
15.86
15.36
T19
2.14
1.79
16.23
T21
3.54
2.75
22.32
T23
3.54
3.10
12.35
T24
2.74
2.10
23.32
T27
3.74
3.17
15.32
T30
2.74
2.40
12.32
T31
2.34
2.05
12.54
Tab.5Error analysis of SSC obtained by MODIS inversion model
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