Remote sensing retrieval of winter wheat leaf area index and canopy chlorophyll density at different growth stages

Figures & data

Figure 1. Distribution of 24 sampling points in Shunyi District, Beijing.

Table 1. Statistical analysis of LCD, LAI and CCD at different growth stages.

Growth stages	Variables	LCD (µg/cm^2)	LAI (m^2/m^2)	CCD (µg/cm^2)
Early jointing	Min	42.952	0.982	44.938
	Max	62.091	3.093	170.975
	Mean	53.421	2.025	108.012
	SD	6.028	0.499	28.071
Late jointing	Min	36.972	2.248	92.627
	Max	60.415	5.627	277.251
	Mean	49.026	3.710	181.196
	SD	5.532	1.067	57.026
Head emergence	Min	49.088	3.354	213.425
	Max	82.885	8.270	546.374
	Mean	60.055	5.791	348.537
	SD	7.972	1.327	98.172
Filling	Min	67.800	3.899	265.724
	Max	101.230	7.751	661.892
	Mean	82.662	5.426	449.640
	SD	10.790	1.121	114.431
Milk development	Min	14.080	2.678	45.539
	Max	66.974	6.329	367.092
	Mean	42.354	4.618	206.950
	SD	14.542	0.879	94.856

Note: SD represents Standard Deviation.

Table 2. Central wavelength and bandwidth of Sentinel-2 spectral bands.

	Sentinel-2A		Sentinel-2B
Band number	Central wavelength(nm)	Bandwidth (nm)	Central wavelength(nm)	Bandwidth(nm)
1	442.7	21	442.2	21
2	492.4	66	492.1	66
3	559.8	36	559.0	36
4	664.6	31	664.9	31
5	704.1	15	703.8	16
6	740.5	15	739.1	15
7	782.8	20	779.7	20
8	832.8	106	832.9	106
8a	864.7	21	864.0	22
9	945.1	20	943.2	21
10	1373.5	31	1376.9	30
11	1613.7	91	1610.4	94
12	2202.4	175	2185.7	185

Table 3. The list of vegetation indices used in this study.

Index	Formulation	Sentinel-2 bands used	Hyperspectral bands used	Reference
NDVI	$\frac{NIR-R}{NIR-R}$	B7, B4	NIR: 783 nm, R: 665 nm	(Rouse et al., 1974)
NDVIre1	$\frac{NIR-re1}{NIR+re1}$	B7, B5	NIR: 783 nm, re: 705 nm,720 nm, 740 nm	(Barnes et al., 2000)
NDVIre2	$\frac{NIR-re2}{NIR+re2}$	B7, B6		Revised index
Maac01	$\frac{R_{780}-R_{710}}{R_{780}-R_{680}}$	B7, B5,B4	780 nm, 710 nm, 680 nm	(Croft et al., 2014)
OSAVI	$(1+L)\ast \frac{NIR-R}{NIR+R+L},L=0.16$	B7, B4	NIR: 783 nm, R: 665 nm	(Rondeaux & Baret, 1996)
OSAVIre1	$\left(1+L\right)\times \frac{NIR-re1}{NIR+re1+L},L=0.16$	B7, B5	NIR: 783 nm, re: 705 nm, 720 nm, 740 nm	Revised index
OSAVIre2		B7, B6
CIgreen	$\frac{NIR}{Green}-1$	B7, B3	NIR:783 nm, Green:550 nm	(Gitelson et al., 2003, Gitelson et al., 2006)
CIred	$\frac{NIR}{R}-1$	B7, B4	NIR: 783 nm, R:665 nm	(Gitelson et al., 2003, Gitelson et al., 2006)
CIre1	$\frac{NIR}{re1}-1$	B7, B5	NIR: 783 nm, re: 705 nm, 720 nm,740 nm	(Gitelson et al., 2003, Gitelson et al., 2006)
CIre2	$\frac{NIR}{re2}-1$	B7, B6		Revised index
MTCIre1	$\frac{NIR-re1}{re1-Red}$	B7, B5, B4	NIR: 783 nm, re: 705 nm, 720 nm, 740 nm	(Dash & Curran, 2004)
MTCIre2	$\frac{NIR-re2}{re2-Red}$	B7, B6, B4		(Dash & Curran, 2004)
MCARI/OSAVI[670,800]	$\frac{\left[\left(R_{700}-R_{670}\right)-0.2\times \left(R_{700}-R_{550}\right)\right]\left(R_{700}/R_{670}\right)}{\left(1+0.16\right)\left(R_{800}-R_{670}\right)/\left(R_{800}+R_{670}+0.16\right)}$	B7, B5, B4, B3	As equations	(Wu et al., 2008)
MCARI/OSAVI[705,750]	$\frac{\left[\left(R_{750}-R_{705}\right)-0.2\times \left(R_{750}-R_{550}\right)\right]\left(R_{750}/R_{705}\right)}{\left(1+0.16\right)\left(R_{750}-R_{705}\right)/\left(R_{750}+R_{705}+0.16\right)}$	B6, B5, B3	As equations	(Wu et al., 2008)
TCARI/OSAVI[670,800]	$\frac{3\left[\left(R_{700}-R_{670}\right)-0.2\times \left(R_{700}-R_{550}\right)\left(R_{700}/R_{670}\right)\right]}{\left(1+0.16\right)\left(R_{800}-R_{670}\right)/\left(R_{800}+R_{670}+0.16\right)}$	B7, B5, B4, B3	As equations	(Wu et al., 2008)
TCARI/OSAVI[705,750]	$\frac{3\left[\left(R_{750}-R_{705}\right)-0.2\times \left(R_{750}-R_{550}\right)\left(R_{750}/R_{705}\right)\right]}{\left(1+0.16\right)\left(R_{750}-R_{705}\right)/\left(R_{750}+R_{705}+0.16\right)}$	B6, B5, B3	As equations	(Wu et al., 2008)

Note: re1 indicates Sentinel-2 Band 5; re2 indicates Sentinel-2 Band 6. VIre1 indicates VI modified with re1; VIre2 indicates VI modified with re2. For hyperspectral data, re indicates red-edge bands include 705 nm, 720 nm, and 740 nm, separately.

Figure 2. Correlation results between LAI, CCD and VI calculated from Sentinel-2 data.

Table 4. RMSE and p-value between vegetation indicese and parameters with Sentinel-2 data

	Index	Early jointing	Late jointing	Head emergence	Filling	Milk development
LAI	NDVI	0.394	0.939	1.213	0.824**	0.680*
	NDVIre1	0.308**	0.937	1.172	0.955	0.689*
	NDVIre2	0.391*	0.936	1.099*	0.938	0.737*
	Maac01	0.467	0.909*	1.224	1.000	0.648*
	OSAVI	0.357*	0.926*	1.191	1.059	0.646*
	OSAVIre1	0.326**	0.933	1.177	0.989	0.695*
	OSAVIre2	0.401*	0.927	1.107*	0.953	0.738
	CIgreen	0.362	0.887*	1.217	0.862*	0.713*
	CIred	0.303**	0.924	1.167	0.976	0.688*
	CIre1	0.303**	0.924	1.167	0.976	0.688*
	CIre2	0.391*	0.935	1.099*	0.937	0.738
	MTCIre1	0.462	0.920*	1.221	0.975	0.639*
	MTCIre2	0.431	0.942	1.110*	0.931	0.748
	MCARI/OSAVI[670,800]	0.469	0.910*	1.094*	0.999	0.581**
	MCARI/OSAVI[705,750]	0.359**	0.921	1.232	0.960	0.747
	TCARI/OSAVI[670,800]	0.474	0.905*	1.092*	0.971	0.623**
	TCARI/OSAVI[705,750]	0.373**	0.968	1.113	1.019	0.689*
CCD	NDVI	21.724	46.852*	90.226	92.961*	61.286**
	NDVIre1	17.589**	45.811*	89.040	85.885*	58.326***
	NDVIre2	20.319**	45.414*	82.642*	91.432*	67.033**
	Maac01	25.208	46.253*	88.696	97.349	49.486***
	OSAVI	20.232	46.045*	89.298	101.209	59.439**
	OSAVIre1	19.078**	45.533*	88.423	91.534*	58.333***
	OSAVIre2	21.054*	44.966*	83.056*	92.743*	66.517**
	CIgreen	20.025*	44.113**	90.801	87.455**	66.709**
	CIred	17.530**	45.193*	89.003	85.864*	57.462***
	CIre1	17.530**	45.193*	89.003	85.864*	57.462***
	CIre2	20.326*	45.427*	82.697*	91.511*	67.038**
	MTCIre1	24.928	46.679*	89.353	96.695*	49.380***
	MTCIre2	24.392	47.519*	82.516*	93.295*	77.202
	MCARI/OSAVI[670,800]	26.044	46.981*	83.405*	105.280	52.698***
	MCARI/OSAVI[705,750]	20.022*	45.690*	89.878	91.586*	58.452***
	TCARI/OSAVI[670,800]	25.703	44.504*	83.145	91.871*	50.477***
	TCARI/OSAVI[705,750]	21.340*	48.773*	82.918*	90.989*	82.050*

Note: *, ** and *** indicates the correlation is significant at the 0.950 confidence level, 0.990 confidence level and 0.999 confidence level, respectively.

Figure 3. Correlation results between LAI, CCD and VI calculated from hyperspectral data.

Table 5. RMSE and p-value between vegetation indices and parameters with hyperspectral data.

	Index	Early jointing	Late jointing	Head emergence	Filling	Milk development
LAI	NDVI	0.421	0.796**	1.124*	0.826**	0.717*
	NDVI705	0.419	0.741**	1.065**	0.840**	0.730
	NDVI720	0.420	0.736**	1.051*	0.798**	0.734
	NDVI740	0.427	0.722*	1.011**	0.627***	0.713
	Maac01	0.388	0.721*	1.008**	0.790**	0.702
	OSAVI	0.427	0.851*	0.982*	0.639***	0.701*
	OSAVI705	0.425	0.798*	0.978*	0.691***	0.709*
	OSAVI720	0.421	0.758**	0.993**	0.722**	0.726
	OSAVI740	0.424	0.721**	0.983**	0.622***	0.713
	CIgreen	0.431	0.755**	1.086*	0.836**	0.787
	CIred	0.433	0.729**	1.062*	0.835**	0.770
	CI705	0.423	0.728**	1.065*	0.837**	0.770
	CI720	0.418	0.734**	1.047*	0.795**	0.751
	CI740	0.427	0.718**	1.010**	0.623***	0.717
	MTCI705	0.373*	0.716**	1.003**	0.812**	0.724
	MTCI720	0.395	0.728**	1.019**	0.758**	0.705
	MTCI740	0.432	0.705**	0.996**	0.594***	0.735
	MCARI/OSAVI[670,800]	0.416	0.981	1.265	0.982	0.791
	MCARI/OSAVI[705,750]	0.431	0.764**	1.001*	0.764**	0.736
	TCARI/OSAVI[670,800]	0.427	0.785*	1.140	0.973**	0.774
	TCARI/OSAVI[705,750]	0.426	0.732**	1.052*	0.844**	0.736
CCD	NDVI	24.105	41.269**	86.425	82.143**	78.019*
	NDVI705	23.069	38.054**	84.376	80.228**	75.609*
	NDVI720	22.362	38.641**	83.610*	74.479***	74.236
	NDVI740	23.053	39.287**	81.296*	65.190***	73.461*
	Maac01	19.410*	37.963**	78.734*	71.752***	70.391*
	OSAVI	24.664	44.660**	82.272	57.631***	76.867*
	OSAVI705	24.052	42.262**	80.701*	58.364***	75.039*
	OSAVI720	23.178	40.752**	80.663*	65.789***	74.049*
	OSAVI740	23.136	39.361**	80.026*	62.428***	73.034*
	CIgreen	23.631	39.698**	86.496	79.834**	80.173
	CIred	23.745	37.528**	84.560	80.054**	77.572
	CI705	23.194	37.454**	84.816	80.418**	77.721
	CI720	22.320	38.483**	83.225*	74.404***	75.216*
	CI740	23.085	39.087**	81.112*	65.064***	73.531*
	MTCI705	19.604	37.438	78.231*	73.499***	72.303*
	MTCI720	20.859	39.112**	80.124*	70.156***	71.624*
	MTCI740	23.333	38.745**	79.718*	63.380***	73.249*
	MCARI/OSAVI[670,800]	21.880	52.912	90.503	91.929**	82.922
	MCARI/OSAVI[705,750]	24.606	39.568**	81.649*	55.910***	77.392*
	TCARI/OSAVI[670,800]	23.149	41.314**	88.291	91.947**	77.738*
	TCARI/OSAVI[705,750]	23.314	37.176**	84.447	79.183**	77.701

Note: *, ** and *** indicates the correlation is significant at the 0.950 confidence level, 0.990 confidence level and 0.999 confidence level, respectively.

Figure 4. Scatterplots of estimated vegetation parameters versus measured vegetation parameters for spectral indices with Sentinel-2 data and hyperspectral data. Red solid lines indicate 1:1 lines. The five rows from up to bottom indicate the validation results at early jointing stage, late jointing stage, head emergence stage, filling stage and milk development stage, separately. The four columns from left to right indicate the vegetation parameters as Sentinel-2 LAI, Sentinel-2 CCD, hyperspectral LAI and hyperspectral CCD.

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Data availability statement

For the moment, the data from the project are not available due to restrictions.