Research on Chlorophyll-a Concentration Retrieval Based on BP Neural Network Model—Case Study of Dianshan Lake, China
Abstract
:1. Introduction
2. Research Data Introduction
2.1. Study Area
2.2. Measured Data
2.3. Landsat-8 Remote Sensing Image
3. Research Methods
3.1. BP Neural Network Modeling Analysis
- (1)
- The input parameter of the BP neural network was the water body reflectivity band combination. The water body reflectivity is related to the nature of the water body. As remote sensing data with the same pre-processing (radiometric calibration, atmospheric correction) were used, and as the image data used were all obtained in winter in the same study area, the homogeneity of the obtained water reflectance remote sensing images was ensured;
- (2)
- The water sample collection method and water Chl-a concentration measurement method were kept consistent for both times, ensuring the reliability and consistency of the accuracy of measured Chl-a concentration accuracy;
- (3)
- The results were derived according to the radiation transfer model formula given in [15]. The bottom reflectance can be ignored, as light cannot reach the bottom of the lake, due to its depth and transparency. Therefore, the main factors affecting the reflectance of the entire water body were the concentration of Chl-a and suspended solids.
3.2. Principle of BP Neural Network Method
3.3. Parameter Selection of BP Neural Network Model
3.4. Construction of BP Neural Network Model
3.5. Construction of Band Combination Model
4. Results
4.1. Results of the BP Neural Network Model
4.2. Results of the Band Combination Model
4.3. Comparative Analysis of Model Results
4.4. Spatiotemporal Analysis of Chl-a Concentration
5. Discussion
6. Conclusions
Author Contributions
Funding
Institutional Review Board Statement
Informed Consent Statement
Data Availability Statement
Acknowledgments
Conflicts of Interest
References
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Sampling Point ID | Longitude (°) | Latitude (°) | Chl-a (μg/L) |
---|---|---|---|
ID1 | 120.9733 | 31.09405 | 4.11 |
ID5 | 120.9301 | 31.1049 | 2.00 |
ID9 | 120.9104 | 31.08038 | 1.42 |
ID16 | 120.9863 | 31.11427 | 1.47 |
ID21 | 120.947 | 31.13484 | 2.27 |
ID25 | 120.9523 | 31.10922 | 5.47 |
ID34 | 120.9283 | 31.07528 | 8.63 |
ID39 | 120.9294 | 31.09667 | 10.54 |
ID40 | 120.9364 | 31.09333 | 10.95 |
ID46 | 120.9297 | 31.10833 | 12.65 |
ID47 | 120.9472 | 31.09389 | 11.70 |
ID56 | 120.9778 | 31.09667 | 13.08 |
ID58 | 120.9636 | 31.10917 | 9.80 |
ID75 | 120.9669 | 31.1325 | 10.95 |
ID76 | 120.9761 | 31.125 | 13.07 |
ID77 | 120.9831 | 31.12028 | 10.95 |
Date | Maximum Value (μg/L) | Minimum Value (μg/L) | Average Value (μg/L) |
---|---|---|---|
21 December 2020 | 6.84 | 0.95 | 3.15 |
14 November 2021 | 16.56 | 7.66 | 10.91 |
All | 16.56 | 0.95 | 8.29 |
Band Name | Band Range (μm) | Spatial Resolution (m) |
---|---|---|
Band1 Coastal | 0.433–0.453 | 30 |
Band2 Blue | 0.450–0.515 | 30 |
Band3 Green | 0.525–0.600 | 30 |
Band4 Red | 0.630–0.680 | 30 |
Band5 NIR | 0.845–0.885 | 30 |
Band6 SWIR1 | 1.560–1.660 | 30 |
Band7 SWIR2 | 2.100–2.300 | 30 |
Band8 PAN | 0.500–0.680 | 15 |
Band9 Cirrus | 1.360–1.390 | 30 |
Band | Correlation |
---|---|
Band1 | −0.59 |
Band2 | −0.36 |
Band3 | −0.12 |
Band4 | −0.10 |
Band5 | −0.01 |
Band6 | −0.16 |
Band7 | −0.46 |
Combination Methods | Correlation Coefficient | Combination Methods | Correlation Coefficient | Combination Methods | Correlation Coefficient |
---|---|---|---|---|---|
B1 + B7 | −0.60 | IN(B3/B2) | 0.56 | B3/B1/(B1 + B7) | 0.79 |
B1 − B2 | −0.71 | IN(B3/B1) | 0.69 | B3/B1/(B1 − B7) | 0.78 |
B1 − B3 | −0.53 | IN(B4/B1) | 0.54 | (B1 − B3)/(B7 − B1) | 0.71 |
B1 − B7 | −0.58 | IN(B1)/IN(B7) | 0.56 | (B1 − B3)/(B1 − B7) | −0.71 |
B2 − B1 | 0.71 | IN(B2)/IN(B1) | −0.51 | (B1 − B3)/(B1 + B7) | −0.70 |
B3 − B1 | 0.53 | IN(B1)/(B1 + B7) | −0.57 | (B2 − B1)/(B7 − B1) | −0.66 |
B7 − B1 | 0.58 | IN(B1)/(B1 − B7) | −0.56 | (B2 − B1)/(B1 − B7) | 0.66 |
B1 × B7 | −0.63 | IN(B1)/(B7 − B1) | 0.56 | (B2 − B1)/(B1 + B7) | 0.67 |
B1/B4 | −0.53 | IN(B3/B1/(B1 + B7)) | 0.79 | (B3 − B1)/(B7 − B1) | −0.71 |
B1/B3 | −0.66 | IN(B3/B1/(B1 − B7)) | 0.77 | (B3 − B1)/(B1 − B7) | 0.71 |
B1/B2 | −0.66 | B3/B1/(B7 − B1) | −0.78 | (B3 − B1)/(B1 + B7) | 0.70 |
B2/B3 | −0.50 | (B1 + B7)/B3/B1 | −0.78 | (B1 − B2)/(B7 − B1) | 0.66 |
B2/B1 | 0.67 | (B1 − B2)/B3/B1 | −0.71 | (B1 − B2)/(B1 − B7) | −0.66 |
B3/B2 | 0.60 | (B1 − B7)/B3/B1 | −0.76 | (B1 − B2)/(B1 + B7) | −0.67 |
B3/B1 | 0.71 | (B1 − B7)/B3/B1 | 0.71 | (B1 + B7) + (B1 − B2) | −0.73 |
IN(B1) | −0.59 | (B7 − B1)/B3/B1 | 0.76 | (B1 + B7) + (B1 − B3) | −0.80 |
IN(B1−B7) | −0.57 | (B1 + B7) − B3/B1 | −0.80 | (B1 + B7) + (B1 − B7) | −0.59 |
IN(B1/B4) | −0.54 | (B1 − B2) − B3/B1 | −0.72 | (B1 − B2) + (B1 − B3) | −0.61 |
IN(B1/B3) | −0.69 | (B1 − B3) − B3/B1 | −0.65 | (B1 − B3) + (B1 − B7) | −0.79 |
IN(B1/B2) | −0.66 | (B1 − B7) − B3/B1 | −0.80 | (B2 − B1) + (B3 − B1) | 0.61 |
IN(B2/B3) | −0.56 | (B2 − B1) − B3/B1 | −0.66 | (B2 − B1) + (B7 − B1) | 0.72 |
IN(B2/B1) | 0.66 | (B3 − B1) − B3/B1 | −0.80 | (B3 − B1) + (B7 − B1) | 0.79 |
Combination Methods | Combination Methods | Combination Methods |
---|---|---|
B1/B3 | B2/B1 | B3/B1 |
B1 − B2 | B1 − B7 | B2 − B1 |
IN(B1/B2) | IN(B1/B3) | IN(B3/B1) |
IN(B1)/(B1 + B7) | IN(B1)/(B1 − B7) | IN(B1)/(B7 − B1) |
(B1 + B7)/B3/B1 | (B1 − B7)/B3/B1 | (B7 − B1)/B3/B1 |
B3/B1/(B1+B7) | B3/B1/(B1 − B7) | B3/B1/(B7 − B1) |
(B1 + B7) − B3/B1 | (B1 − B7) − B3/B1 | (B3 − B1) − B3/B1 |
(B1 − B3)/(B1 − B7) | (B3 − B1)/(B7 − B1) | (B3 − B1)/(B1 − B7) |
(B1 + B7) + (B1 − B3) | (B1 − B3) + (B1 − B7) | (B3 − B1) + (B7 − B1) |
Model | Input Variable | Removed Variable | Method |
---|---|---|---|
1 | (B1 − B3) + (B1 − B7), (B3 − B1) − B3/B1, (B1 + B7) + (B1 − B3) b | (B1 + B7) − B3/B1, (B1 − B7) − B3/B1 | Enter |
Model | R | R-Squared | Adjusted R-Squared | Error in Standard Estimation |
---|---|---|---|---|
1 | 0.782 a | 0.611 | 0.591 | 2.629596385113078 |
Model | Unstandardized Coefficients | Standardized Coefficient | t | Salience | |||
---|---|---|---|---|---|---|---|
B | Standard Error | Beta | |||||
1 | Constant | −12.949 | 44.674 | −0.290 | 0.773 | ||
(B3 − B1) − B3/B1 | −29.212 | 33.787 | −0.397 | −0.865 | 0.391 | ||
(B1 + B7) + (B1 − B3) | −71.715 | 46.722 | −2.218 | −1.535 | 0.130 | ||
(B1 − B3) + (B1 − B7) | 61.410 | 46.942 | 1.840 | 1.308 | 0.196 |
Independent Variable | Model | Fitting Equation | R−Squared |
---|---|---|---|
(B1 + B7) − B3/B1 | Linear function | Chl-a = − 17.445x − 1.9969 | 0.60 |
Quadratic function | Chl-a = 12.581x2 − 3.9426x + 1.1729 | 0.61 | |
Cubic function | Chl-a = 141.29x3 + 232.44x2 + 101.5x + 16.359 | 0.65 | |
Exponential function | Chl-a = 1.0733e−3.121x | 0.58 |
Index | Band Combination Model—Multiple Regression Analysis | Band Combination Model—Curve Estimation Analysis | BP Neural Network Model |
---|---|---|---|
R-Squared | 0.80 | 0.87 | 0.86 |
RMSE (μg/L) | 2.08 | 1.72 | 1.69 |
MRE (%) | 23.62 | 22.45 | 19.48 |
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Zhu, W.-D.; Qian, C.-Y.; He, N.-Y.; Kong, Y.-X.; Zou, Z.-Y.; Li, Y.-W. Research on Chlorophyll-a Concentration Retrieval Based on BP Neural Network Model—Case Study of Dianshan Lake, China. Sustainability 2022, 14, 8894. https://doi.org/10.3390/su14148894
Zhu W-D, Qian C-Y, He N-Y, Kong Y-X, Zou Z-Y, Li Y-W. Research on Chlorophyll-a Concentration Retrieval Based on BP Neural Network Model—Case Study of Dianshan Lake, China. Sustainability. 2022; 14(14):8894. https://doi.org/10.3390/su14148894
Chicago/Turabian StyleZhu, Wei-Dong, Chu-Yi Qian, Nai-Ying He, Yu-Xiang Kong, Zi-Ya Zou, and Yu-Wei Li. 2022. "Research on Chlorophyll-a Concentration Retrieval Based on BP Neural Network Model—Case Study of Dianshan Lake, China" Sustainability 14, no. 14: 8894. https://doi.org/10.3390/su14148894