Area extraction and growth monitoring of sugarcane from multi-source remote sensing images under a polarimetric SAR data compensation based on buildings

Figures & data

Figure 1. Study area and sample collection area (a), sugarcane in elongation stage (b), and sample sites in sample collection area (c).

Table 1. Growth stages of main crops in Chongzuo City.

Crop	Jan.	Feb.		Mar.	Apr.	May.	Jun.	Jul.	Aug.	Sep.	Oct.	Nov.	Dec.
Sugarcane	Harvest			Sow	Grow							Mature
Rice					Sow	Grow		Mature/Sow	Grow		Mature
Banana	Harvest		Sow		Grow							Mature

Figure 2. Radiometric calibration and error compensation proposed in this study.

Table 2. Sample area and sample size in this experiment.

Crop category	Sugarcane	Banana	Rice	Forest	Buildings	Water	Others
Sample area (kha)	6.45	6.44	4.37	8.12	6.78	7.01	4.58
Sample size	630	420	227	479	187	162	325

Figure 3. Descriptive statistics of the ground truth of sugarcane height.

Figure 4. Flowchart of technical route.

Figure 5. Time sequence diagram of mean values of VH in 6 objects in 2022 (the shaded areas refer to the standard deviation calculated from the sample points).

Table 3. Evaluation of correlation of backscatter coefficient among six objects.

Correlation coefficient	Sugarcane	Banana	Rice	Water	Buildings	Forest
Sugarcane	-	0.82	0.75	0.90	0.67	0.77
Banana	0.82	-	0.61	0.72	0.56	0.84
Rice	0.75	0.61	-	0.86	0.28	0.83
Water	0.90	0.72	0.86	-	0.55	0.84
Buildings	0.67	0.56	0.28	0.55	-	0.34
Forest	0.77	0.84	0.83	0.84	0.34	-

Figure 6. Accuracy evaluation of sugarcane extraction by different calibration methods.

Table 4. Accuracy evaluation of sugarcane extraction with different data combinations.

Test	Features	Data source	PA (%)	UA (%)	F1%)
1	Optical data	Sentinel-2	85.46	85.45	85.45
2	VH03+ VH05	Sentinel-1	88.55	78.93	83.47
3	Optical data +VH03+ VH05	Sentinel-1, Sentinel-2	92.57	88.74	90.61
4	Optical data +SGI	Sentinel-1, Sentinel-2	94.82	89.56	92.12

Figure 7. Extraction results of sugarcane in Chongzuo city.

Figure 8. Normalized (AIC + BIC) metric of GMM fitting for sugarcane area in 2022.

Figure 9. GMM distribution fitting diagram in the seedling stage (a), AIC+BIC metric chart in the seedling stage (b), GMM distribution fitting diagram in the elongation stage (c), and AIC+BIC metric chart in the elongation stage (d).

Table 5. Accuracy evaluation of extraction of newly planted sugarcane and ratoon sugarcane in Jiangzhou district.

Index	Without compensation			Compensation by the multiplicative model
	Newly planted sugarcane	Ratoon sugarcane	Sugarcane	Newly planted sugarcane	Ratoon sugarcane	Sugarcane
Statistical area (khm^2)	23.8	52.9	76.7	23.8	52.9	76.7
Extraction area(khm^2)	26.3	40.6	66.9	28.1	42.6	70.7
Parea (%)	89.50	76.75	87.22	82.06	80.59	92.18

Figure 10. Estimation results of sugarcane height: without compensation (a), compensation by the additive model (b), compensation by the multiplicative model (c), and estimation results of sugarcane height (d).

Table 6. Accuracy evaluation of sugarcane extraction with different data combinations.

Compensation model	Model	R^2	RMSE (m)
Without compensation	Linear	0.609	0.471
	Quadratic polynomial	0.613	0.468
	Exponential	0.588	0.483
Compensation by the additive model	Linear	0.678	0.428
	Quadratic polynomial	0.681	0.425
	Exponential	0.647	0.431
Compensation by the multiplicative model	Linear	0.712	0.405
	Quadratic polynomial	0.717	0.403
	Exponential	0.689	0.429

Figure 11. Accuracy evaluation of sugarcane extraction under different feature combinations.

Table 7. Evaluation of additive and multiplicative compensation models.

Object	Evaluation index	Without compensation	Compensation by the additive model	Compensation by the multiplicative model
Sugarcane	Std (dB)	1.489	1.303	1.244
	CV	-0.087	-0.076	-0.073
Forest	Std (dB)	0.620	0.587	0.581
	CV	-0.041	-0.039	-0.039

Figure 12. Sugarcane region comparison before and after calibration of time series SAR data.

Data availability statement

Upon reasonable request, the corresponding author will provide access to the data used to support the study’s findings.