Estimation of Soil Organic Carbon Content by Imaging Spectroscopy With Soil Roughness

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Fig. 1. The geographical location of study area and the distribution of soil samples

Fig. 2. RGB images of the single soil sample before and after grinding
R: 638 nm, G: 550 nm, B: 470 nm

Fig. 3. The mean reflectances of imaging spectra (d, b) and non-imaging spectra (c, a) of the soil samples before and after grinding

Fig. 4. The correlation coefficient between imaging spectra (d, b)/non-imaging spectra (c, a) and SOC for the soil samples before and after grinding

Fig. 5. The VIP of imaging spectra (d, b)/non-imaging spectra (c, a) of the soil samples before and after grinding

样本集	样本量/个	土壤有机碳含量/%				标准差	变异系数	偏度系数	峰度系数
样本集	样本量/个	最大值	最小值	平均值	中位数	标准差	变异系数	偏度系数	峰度系数
样本全集	60	2.97	1.21	2.22	2.33	0.43	0.19	-0.72	-0.28
建模集	40	2.97	1.21	2.22	2.33	0.44	0.20	-0.71	-0.29
验证集	20	2.83	1.24	2.22	2.33	0.42	0.19	-0.82	0.04

Table 1. The statistical description of SOC content

样本预处理	光谱预处理		光谱类型		偏最小二乘回归								支持向量回归
					建模集				验证集				建模集				验证集
					R²		RMSE		R²		RMSE		R²		RMSE		R²	RMSE
未研磨样本	None		Imaging		0.788		0.040		0.739		0.045		0.804		0.037		0.712	0.050
	None		Non-imaging		0.703		0.056		0.344		0.114		0.721		0.053		0.311	0.119
	CR		Imaging		0.797		0.039		0.651		0.060		0.789		0.040		0.705	0.051
	CR		Non-imaging		0.948		0.010		0.196		0.139		0.672		0.062		0.469	0.092
	AB		Imaging		0.785		0.041		0.719		0.049		0.808		0.036		0.699	0.052
	AB		Non-imaging		0.735		0.050		0.411		0.102		0.788		0.040		0.281	0.125
	SG		Imaging		0.788		0.040		0.739		0.045		0.804		0.037		0.712	0.050
	SG		Non-imaging		0.699		0.057		0.347		0.113		0.717		0.054		0.299	0.122
	SNV		Imaging		0.795		0.039		0.719		0.049		0.802		0.038		0.735	0.046
	SNV		Non-imaging		0.703		0.056		0.396		0.105		0.719		0.053		0.410	0.102
	MSC		Imaging		0.794		0.039		0.718		0.049		0.797		0.039		0.724	0.048
	MSC		Non-imaging		0.703		0.056		0.398		0.104		0.700		0.057		0.394	0.105
研磨样本		None		Imaging		0.743		0.049		0.648		0.061		0.848		0.029	0.716	0.049
		None		Non-imaging		0.774		0.043		0.645		0.062		0.799		0.038	0.706	0.051
		CR		Imaging		0.733		0.051		0.666		0.058		0.830		0.032	0.724	0.048
		CR		Non-imaging		0.858		0.027		0.564		0.076		0.836		0.031	0.708	0.051
		AB		Imaging		0.794		0.039		0.709		0.051		0.849		0.029	0.731	0.047
		AB		Non-imaging		0.782		0.041		0.693		0.053		0.751		0.047	0.614	0.067
		SG		Imaging		0.743		0.049		0.648		0.061		0.848		0.029	0.716	0.049
		SG		Non-imaging		0.774		0.043		0.645		0.062		0.798		0.038	0.706	0.051
		SNV		Imaging		0.727		0.052		0.626		0.065		0.783		0.041	0.738	0.045
		SNV		Non-imaging		0.768		0.044		0.657		0.059		0.788		0.040	0.693	0.053
		MSC		Imaging		0.722		0.053		0.622		0.066		0.782		0.041	0.736	0.046
		MSC		Non-imaging		0.767		0.044		0.655		0.060		0.788		0.040	0.692	0.053

Table 2. PLSR and SVR model performances based on imaging spectra/non-imaging spectra of the soil samples before and after grinding

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