Canopy Nitrogen Concentration Monitoring Techniques of Summer Corn Based on Canopy Spectral Information
Abstract
:1. Introduction
2. Materials and Methods
2.1. Brief Information of Experiment Area
2.2. Experiment Design
2.3. Items to Be Measured and Methods
2.3.1. Monitoring of Canopy Spectra
2.3.2. Determination of Canopy Nitrogen Concentration
2.3.3. Data Processing and Statistical Analysis
3. Results
3.1. Canopy Nitrogen Concentration and Yield of Summer Corn under Different Nitrogen Levels
3.2. Canopy Spectral Characteristics of Summer Corn under Different Nitrogen Levels
3.3. Sensitive Bands for Spectral Monitoring of Canopy Nitrogen in Summer Corn
3.4. Selecting Optimal Index Model for Monitoring Canopy Nitrogen Concentration in Summer Corn
3.5. Spectral Monitoring Technology of Canopy Nitrogen Concentration in Summer Corn
4. Discussion
5. Conclusions
- (1)
- The canopy reflectance of the plants is low due to the absorption by chlorophyll in the visible light band, but the multi-scattering effect of the canopy cell structure in the near-infrared region leads to a higher reflectance in this band. At the point of fertilization, the canopy spectral reflectance of summer corn plants in the visible light band decreases with the increase of fertilization, but the trend is reversed in the near infrared band.
- (2)
- Choosing the bands to which the plant canopy nitrogen concentration is sensitive reduces the redundancy of spectral information and improves the prediction accuracy of the spectral models. Investigation is made into the correlation between the summer corn plant canopy spectral reflectance and its first derivative on the one hand and the canopy nitrogen concentration on the other. From the correlation and factoring in the optimal band combination determined by the stepwise discriminant analysis, the sensitive bands for monitoring the canopy nitrogen concentration using the original spectra and their first derivative are found to be 762 nm and 726 nm respectively, the optimal combination of bands is 762 nm, 944 nm and 957 nm.
- (3)
- A total of 55 published nitrogen spectral monitoring index models were examined for the correlation between their calculated values and the measured values of the canopy nitrogen concentration. Five spectral index models with higher correlation coefficients are retained, namely mNDVI, NDRE, R780/R740, ND (FD730, FD525) and CCCI, and the principle of highest correlation at key growth period was taken into account, NDRE is recommended as the most suitable spectral index model for monitoring nitrogen concentration in summer corn canopy.
- (4)
- Once the sensitive bands were determined, the suitable spectral index model recommended, and the optimal band combination known, four models, namely the sensitive band reflectance model, the sensitive band reflectance first derivative model, the optimal band combination model, and the suitable spectral index model, were constructed and demonstrated to perform well in predicting summer corn canopy nitrogen concentration. The four models come in the following descending order of prediction accuracy: the suitable spectral index model, the optimal band combination model, the sensitive band reflectance first derivative model, and the sensitive band reflectance model.
Author Contributions
Funding
Acknowledgments
Conflicts of Interest
References
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Degree of Depth (cm) | Initial Nitrate Nitrogen Concentration (mg/kg) | Initial Ammonium Nitrogen Concentration (mg/kg) |
---|---|---|
0−20 | 5.558 | 3.231 |
20−40 | 2.803 | 2.773 |
40−60 | 2.288 | 2.710 |
60−80 | 2.534 | 2.532 |
Spectral Characteristic Variable | Jointing Period | Tasseling Period | Filling Period | Maturity Period | Whole Growth Period | |
---|---|---|---|---|---|---|
spectral reflectance | Characteristic band (nm) | 799 | 937 | 774 | 762 | 762 |
Correlation coefficient | 0.160 | 0.526 * | 0.578 ** | 0.280 | 0.550 ** | |
first derivative spectral reflectance | Characteristic band (nm) | 737 | 752 | 738 | 714 | 726 |
Correlation coefficient | 0.285 | 0.659 ** | 0.767 ** | 0.636** | 0.795 ** |
Category | Spectral Parameters | Definition | Reference |
---|---|---|---|
Spectral characteristic parameters | Green peak amplitude, Rg | Maximum band reflectance within the green band of 510−560 nm | [5] |
Red trough amplitude, Rr | Minimum band reflectance within the red band of 640−680 nm | [5] | |
(Rg – Rr) /(Rg + Rr) | Normalized value of green peak reflectance and red trough reflectance | [5] | |
Rg/Rr | Ratio between green peak reflectance and red trough reflectance | [5] | |
Red trough skewness, Sr | Band reflectance skewness within 640−680 nm region | [24] | |
Red trough kurtosis, kr | Band reflectance kurtosis within 640−680 nm region | [24] | |
Green peak skewness, Sg | Band reflectance skewness within 510−560 nm region | [24] | |
Green peak kurtosis, kg | Band reflectance kurtosis within 510−560 nm region | [24] | |
Sg/Sr | Ratio between green peak skewness (Sg) and red trough skewness (Sr) | [24] | |
kg/kr | Ratio between green peak kurtosis (kg) and red trough kurtosis (kr) | [24] | |
(Sg – Sr)/(Sg + Sr) | Normalized value of green peak skewness (Sg) and red trough skewness (Sr) | [24] | |
(kg – kr)/(kg + kr) | Normalized value of green peak kurtosis (kg) and red trough kurtosis (kr) | [24] | |
depth670 | Vegetation absorption depth at 670 nm | [25] | |
Area670 | Vegetation absorption characteristic area at 560−760 nm, or the area between the envelope and the spectral reflectance in the spectral range of 560−760 nm. | [25] | |
ND670 | Normalized vegetation absorption depth at 670 nm, or the ratio between absorption depth and absorption characteristic area | [25] | |
Red edge amplitude, Dr | Maximum first differential value of red edge in 680−760 nm region | [26] | |
Blue edge amplitude, Db | Maximum first differential value of blue edge in 490−530 nm region | [26] | |
Yellow edge amplitude, Dy | Maximum first differential value of yellow edge in 550−582 nm region | [26] | |
Red edge area, SDr | Sum of first differential band values in the red edge waveband | [26] | |
Blue edge area, SDb | Sum of first differential band values in the blue edge waveband | [26] | |
Yellow edge area, SDy | Sum of first differential band values in the yellow edge waveband | [26] | |
SDr/SDb | Ratio between the sum of first differential values in the red edge and that in the blue edge | [26] | |
SDr/SDy | Ratio between the sum of first differential values in the red edge and that in the yellow edge | [26] | |
SDr – SDb | Difference between the sum of first differential values in the red edge and that in the blue edge | [26] | |
(SDr – SDb)/(SDr + SDb) | Normalized value of the sum of first differential values in the red edge and that in the blue edge | [26] | |
(SDr – SDy)/(SDr + SDy) | Normalized value of the sum of first differential values in the red edge and that in the yellow edge | [26] | |
Spectral vegetation index | NPCI | (R430 − R680)/(R430 + R680) | [5] |
PRIb | (R570 − R539)/(R570 + R539) | [5] | |
Soil adjustment vegetation index, SAVI | 1.5 × (R870 − R680)/(R870 + R680 + 0.5) | [5] | |
RVI (950, 660) | R950/R660 | [6] | |
RVI (810, 660) | R810/R660 | [6] | |
NRI | R800/R550 | [9] | |
RVI (810, 560) | R810/R560 | [9] | |
DCNI | (R720 − R700)/(R700 − R670)/(R720 − R670 + 0.03) | [9] | |
MSR sum | (RNIR/RRED – 1)/(RNIR/RRED + 1)^0.5 | [27] | |
RNIR/RRED: ratio between sum of reflectance values in the near-infrared band (700−1075 nm) and that in the red light band (620−750 nm) | |||
MSR mean | (RNIR/RRED – 1)/(RNIR/RRED + 1)^0.5 | [27] | |
RNIR/RRED: ratio between mean of reflectance values in the near-infrared band (700−1075nm) and that in the red light band (620−750 nm) | |||
ND (FD730 , FD525) | (R′730 − R′525)/(R′730 + R′525) | [28] | |
ND (573, 440) | (R573 − R440)/(R573 + R440) | [28] | |
R810 – R680 | R810 − R680 | [28] | |
RVI (780, 740) | R780/R740 | [29] | |
RVI (760, 510) | R760/R510 | [30] | |
RVI (760, 460) | R760/R460 | [30] | |
ND (760, 510) | (R760 − R510)/(R760 + R510) | [30] | |
ND (740, 460) | (R740 − R460)/(R740 + R460) | [30] | |
RSI (FD691 , FD711) | RSI(FD691, FD711) = R′691/R′711 | [31] | |
CCCI | ((R780 − R720)/(R780 + R720)) /((R780 − R670)/(R780 + R670)) | [32] | |
NDRE | (R780 − R720)/(R780 + R720) | [32] | |
mNDVI | (R816 − R732 × R537)/(R816 + R732 + R537) | [33] | |
BNI | R434/(R496 + R401) | [33] | |
mNDVI | (R924 − R703 + 2 × R423)/(R924 + R703 – 2 × R423) | [33] | |
R′729 | R′729 | [34] | |
RNIR – RRED MAX | Difference between maximum reflectance value in the near-infrared band (700−1075 nm) and that in the red light band (620−750 nm) | [35] | |
RNIR – RRED MIN | Difference between minimum reflectance value in the near-infrared band (700−1075 nm) and that in the red light band (620−750 nm) | [35] | |
RNIR – RRED sum | Difference between sum of reflectance values in the near-infrared band (700−1075 nm) and that in the red light band (620−750 nm) | [35] | |
RNIR – RRED mean | Difference between mean of reflectance values in the near-infrared band (700−1075 nm) and that in the red light band (620−750 nm) | [35] |
Spectral Index | Whole Growth Period | Jointing Period | Tasseling Period | Filling Period | Maturity Period | |
---|---|---|---|---|---|---|
1 | Green peak amplitude, Rg | −0.344 | −0.509 | 0.345 | 0.025 | −0.167 |
2 | Red trough amplitude, Rr | −0.542 | −0.421 | 0.533 | −0.407 | −0.167 |
3 | (Rg – Rr)/(Rg + Rr) | 0.743 | 0.004 | −0.680 | 0.460 | 0.054 |
4 | Rg/Rr | 0.716 | 0.026 | −0.668 | 0.437 | 0.043 |
5 | Red trough skewness, Sr | 0.087 | 0.278 | 0.075 | 0.355 | 0.333 |
6 | Red trough kurtosis, kr | −0.243 | 0.242 | 0.023 | −0.066 | 0.297 |
7 | Green peak skewness, Sg | −0.407 | −0.285 | −0.236 | −0.669 | 0.535 |
8 | Green peak kurtosis, kg | 0.534 | 0.301 | 0.257 | 0.549 | −0.574 |
9 | Sg/Sr | −0.078 | 0.206 | −0.134 | −0.131 | 0.389 |
10 | kg/kr | 0.398 | −0.082 | 0.213 | 0.215 | −0.443 |
11 | (Sg – Sr)/(Sg + Sr) | 0.283 | −0.251 | −0.118 | −0.107 | 0.016 |
12 | (kg – kr)/(kg + kr) | 0.355 | −0.087 | 0.215 | 0.184 | −0.468 |
13 | depth670 | 0.701 | 0.325 | −0.122 | 0.529 | 0.286 |
14 | Area670 | −0.349 | −0.506 | 0.414 | 0.031 | −0.145 |
15 | ND670 | 0.603 | 0.378 | −0.264 | 0.544 | 0.268 |
16 | Red edge amplitude, Dr | 0.498 | −0.300 | 0.557 | 0.542 | 0.035 |
17 | Blue edge amplitude, Db | 0.167 | −0.434 | 0.065 | 0.086 | −0.229 |
18 | Yellow edge amplitude, Dy | −0.571 | 0.565 | 0.231 | −0.357 | 0.140 |
19 | Red edge area, SDr | 0.706 | −0.290 | 0.471 | 0.479 | 0.231 |
20 | Blue edge area, SDb | 0.044 | −0.514 | −0.145 | −0.074 | −0.236 |
21 | Yellow edge area, SDy | −0.612 | 0.481 | −0.237 | −0.348 | −0.244 |
22 | SDr/SDb | 0.605 | 0.370 | 0.621 | 0.638 | 0.516 |
23 | SDr/SDy | 0.108 | −0.380 | −0.045 | 0.526 | 0.016 |
24 | SDr – SDb | 0.741 | −0.181 | 0.527 | 0.520 | 0.353 |
25 | (SDr – SDb)/(SDr + SDb) | 0.608 | 0.419 | 0.602 | 0.678 | 0.538 |
26 | (SDr – SDy)/(SDr + SDy) | 0.612 | −0.429 | −0.106 | 0.306 | 0.275 |
27 | NPCI | 0.773 | −0.149 | 0.740 | 0.734 | 0.313 |
28 | PRIb | −0.782 | −0.321 | −0.399 | −0.563 | −0.243 |
29 | Soil adjustment vegetation index, SAVI | 0.762 | −0.098 | 0.410 | 0.523 | 0.327 |
30 | RVI (950,660) | 0.694 | 0.314 | −0.028 | 0.496 | 0.293 |
31 | RVI (810,660) | 0.693 | 0.313 | −0.135 | 0.519 | 0.292 |
32 | NRI = R800/R550 | 0.612 | 0.368 | 0.188 | 0.496 | 0.423 |
33 | RVI (810, 560) | 0.611 | 0.371 | 0.259 | 0.514 | 0.412 |
34 | DCNI | 0.453 | 0.420 | 0.293 | 0.330 | 0.425 |
35 | MSR sum | 0.754 | 0.359 | 0.225 | 0.615 | 0.425 |
36 | MSR mean | 0.754 | 0.359 | 0.226 | 0.615 | 0.424 |
37 | ND (FD730,FD525) | 0.680 | 0.477 | 0.624 | 0.682 | 0.543 |
38 | ND (573, 440) | 0.195 | −0.052 | −0.810 | −0.892 | −0.453 |
39 | R810 – R680 | 0.613 | −0.255 | 0.473 | 0.476 | 0.205 |
40 | RVI (780, 740) | 0.687 | 0.372 | 0.637 | 0.718 | 0.522 |
41 | RVI (760, 510) | 0.611 | 0.328 | −0.283 | 0.346 | 0.248 |
42 | RVI (760, 460) | 0.604 | 0.318 | −0.474 | 0.175 | 0.203 |
43 | ND (760, 510) | 0.702 | 0.315 | −0.339 | 0.372 | 0.286 |
44 | ND (740, 460) | 0.610 | 0.266 | −0.603 | 0.013 | 0.170 |
45 | RSI (FD691, FD711) | −0.612 | −0.586 | −0.409 | −0.539 | −0.478 |
46 | CCCI | 0.615 | 0.412 | 0.694 | 0.703 | 0.547 |
47 | NDRE | 0.771 | 0.390 | 0.524 | 0.735 | 0.569 |
48 | mNDVI = (R816 – R732 – R537) /(R816 + R732 + R537) | 0.704 | 0.384 | 0.444 | 0.590 | 0.468 |
49 | BNI | 0.402 | 0.018 | −0.113 | 0.569 | 0.145 |
50 | mNDVI = (R924 – R703 + 2 × R423) (R924 + R703 – 2 × R423) | 0.738 | 0.451 | 0.799 | 0.864 | 0.538 |
51 | R′729 | 0.767 | −0.031 | 0.593 | 0.607 | 0.458 |
52 | RNIR – RRED MAX | −0.402 | 0.276 | 0.609 | 0.039 | 0.080 |
53 | RNIR – RRED MIN | −0.297 | −0.512 | −0.241 | −0.176 | −0.279 |
54 | RNIR – RRED sum | 0.352 | −0.342 | 0.498 | 0.420 | 0.029 |
55 | RNIR – RRED mean | 0.606 | −0.181 | 0.511 | 0.485 | 0.226 |
Ranking | Whole Growth Period | Jointing Period | Tasseling Period | Filling Period | Maturity Period |
---|---|---|---|---|---|
1 | PRIb | RSI(FD691,FD711) | ND(573,440) | ND(573,440) | kg |
2 | NPCI | Dy | mNDVI-1 | mNDVI-1 | NDRE |
3 | NDRE | SDb | NPCI | NDRE | CCCI |
4 | R′729 | RNIR-RRED MIN | CCCI | NPCI | ND (FD730, FD525) |
5 | SAVI | Rg | (Rg − Rr)/(Rg + Rr) | RVI(780,740) | (SDr − SDb) /(SDr + SDb) |
6 | MSR mean | Area670 | Rg/Rr | CCCI | mNDVI-1 |
7 | MSR sum | SDy | RVI(780,740) | ND (FD730, FD525) | Sg |
8 | (Rg − Rr) /(Rg + Rr) | ND (FD730,FD525) | ND (FD730 ,FD525) | (SDr − SDb) /(SDr + SDb) | RVI (780, 740) |
9 | SDr − SDb | mNDVI-1 | SDr/SDb | Sg | SDr/SDb |
10 | mNDVI-1 | Db | RNIR-RRED MAX | SDr/SDb | RSI (FD691, FD711) |
11 | Rg/Rr | (SDr − SDy)/(SDr + SDy) | ND (740,460) | MSR mean | mNDVI-2 |
12 | SDr | Rr | (SDr − SDb) /(SDr + SDb) | MSR sum | (kg − kr)/(kg + kr) |
13 | mNDVI-2 | DCNI | R′729 | R′729 | R′729 |
14 | ND (760, 510) | (SDr – SDb)/(SDr + SDb) | Dr | mNDVI-2 | ND (573, 440) |
15 | depth670 | CCCI | Rr | BNI | kg/kr |
16 | RVI (950, 660) | NDRE | SDr − SDb | PRIb | DCNI |
17 | RVI (810, 660) | mNDVI-2 | NDRE | kg | MSR sum |
18 | RVI (780, 740) | SDr/SDy | RNIR-RRED mean | ND670 | MSR mean |
19 | ND (FD730, FD525) | ND670 | RNIR-RRED sum | Dr | NRI = R800/R550 |
20 | CCCI | RVI (780, 740) | RVI (760, 460) | RSI (FD691, FD711) | RVI (810, 560) |
Spectral Index | Whole Growth Period | Jointing Period | Tasseling Period | Filling Period | Maturity Period |
---|---|---|---|---|---|
mNDVI = (R924 − R703 + 2 × R423) /(R924 + R703 − 2 × R423) | 0.771 ** | 0.451 * | 0.799 ** | 0.864 ** | 0.569 ** |
NDRE = (R780 − R720)/(R780 + R720) | 0.738 ** | 0.390 | 0.524 * | 0.735 ** | 0.538 ** |
R780/R740 | 0.687 ** | 0.372 | 0.637 ** | 0.718 ** | 0.522 ** |
ND(FD730, FD525) = (R′730 − R′525)/(R′730 + R′525) | 0.680 ** | 0.477 * | 0.624 ** | 0.682 ** | 0.543 ** |
CCCI = ((R780 − R720)/(R780 + R720))/ ((R780 − R670)/(R780 + R670)) | 0.615 ** | 0.412 | 0.694 ** | 0.703 ** | 0.547 ** |
Spectral Index | Whole Growth Period | Jointing Period | Tasseling Period | Filling Period | Maturity Period |
---|---|---|---|---|---|
mNDVI = (R924 − R703 + 2 × R423) /(R924 + R703 − 2 × R423) | 0.849 ** | 0.319 | 0.821** | 0.744** | 0.589** |
NDRE = (R780 − R720)/(R780 + R720) | 0.856 ** | 0.550 ** | 0.692 ** | 0.583 ** | 0.584 ** |
R780/R740 | 0.824 ** | 0.579 ** | 0.714 ** | 0.591 ** | 0.436 * |
ND (FD730, FD525) = (R′730 − R′525)/(R′730 + R′525) | 0.778 ** | 0.831 ** | 0.799 ** | 0.548 ** | 0.328 |
CCCI = ((R780 − R720)/(R780 + R720))/ ((R780 – R670)/(R780 + R670)) | 0.762 ** | 0.548 ** | 0.746 ** | 0.761 ** | 0.363 |
Spectral Index | Whole Growth Period | Jointing Period | Tasseling Period | Filling Period | Maturity Period |
---|---|---|---|---|---|
mNDVI = (R924 − R703 + 2 × R423) /(R924 + R703 − 2 × R423) | 0.618 ** | 0.509 * | 0.818 ** | 0.855 ** | 0.884 ** |
NDRE = (R780 − R720)/(R780 + R720) | 0.696 ** | 0.470 * | 0.600 ** | 0.673 ** | 0.808 ** |
R780/R740 | 0.543 ** | 0.477 * | 0.597 ** | 0.662 ** | 0.904 ** |
ND (FD730, FD525) = (R′730 − R′525)/(R′730 + R′525) | 0.566 ** | 0.563 ** | 0.721 ** | 0.636 ** | 0.936 ** |
CCCI = ((R780 − R720)/(R780 + R720))/ ((R780 − R670)/(R780 + R670)) | 0.511 * | 0.612 ** | 0.755 ** | 0.774 ** | 0.884 ** |
Spectral Parameters | Fitted Model | Model Evaluation Indexes | ||
---|---|---|---|---|
R2 | RMSE (g.g–1) | MAE (g.g–1) | ||
762 nm | y = 3.3749R7620.8638 | 0.306 | 0.514 | 0.413 |
726 nm | y = 42.042 (R726′)0.6537 | 0.639 | 0.368 | 0.298 |
762 nm, 944 nm, 957 nm | y = 0.881 − 10.194R762 − 20.056R957 + 11.469R944 | 0.711 | 0.328 | 0.262 |
NDRE | y = 5.6378x2 + 0.48x + 0.791 | 0.754 | 0.322 | 0.258 |
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Liu, L.; Peng, Z.; Zhang, B.; Wei, Z.; Han, N.; Lin, S.; Chen, H.; Cai, J. Canopy Nitrogen Concentration Monitoring Techniques of Summer Corn Based on Canopy Spectral Information. Sensors 2019, 19, 4123. https://doi.org/10.3390/s19194123
Liu L, Peng Z, Zhang B, Wei Z, Han N, Lin S, Chen H, Cai J. Canopy Nitrogen Concentration Monitoring Techniques of Summer Corn Based on Canopy Spectral Information. Sensors. 2019; 19(19):4123. https://doi.org/10.3390/s19194123
Chicago/Turabian StyleLiu, Lu, Zhigong Peng, Baozhong Zhang, Zheng Wei, Nana Han, Shaozhe Lin, He Chen, and Jiabing Cai. 2019. "Canopy Nitrogen Concentration Monitoring Techniques of Summer Corn Based on Canopy Spectral Information" Sensors 19, no. 19: 4123. https://doi.org/10.3390/s19194123