A remote sensing index for the detection of multi-type water quality anomalies in complex geographical environments

Figures & data

Figure 1. The spectral reflectance curves of different earth’s surfaces.

Table 1. The acquisition time and location information of the selected Sentinel-2 data.

Anomaly type	Acquisition time	Location	Latitude and longitude of the area center
Water blooms	July 27, 2022	Tai Laker, China	120.092° E and 31.388° N
Green tides	July 13, 2019	Jiaozhou Bay, China	120.307° E and 36.021° N
Red tides	July 18, 2019	Florida, USA	82.151° W and 26.847° N
Black and odorous water	August 18, 2020	Xinyang, China	114.004° E and 32.132° N
Floods with light yellow	November 16, 2021	Washington State, USA	122.683° W and 48.765° N
Floods with light green	August 31, 2022	Mehar, Pakistan	67.861° E and 27.121° N
Oil spill	March 23, 2020	Jeolla Province, South Korea	127.732° E and 34.856° N
Water pollution	August 18, 2020	Xinyang, China	114.002° E and 32.124° N
Forest	July 24, 2022	Shangluo, China	110.364° E and 34.301° N
Grassland with high vegetation coverage	July 6, 2021	Vaibaikal Krai, Russia	119.216° E and 50.914° N
Grassland with low vegetation coverage	July 1, 2022	Oriental Province, Mongolia	118.898° E and 47.196° N
Barren land	July 7, 2021	Inner Mongolia, China	112.823° E and 43.112° N
Artificial surface	July 8, 2021	Beijing, China	116.412° E and 39.859° N
Ice and snow	July 3, 2021	Svalbard Archipelago, Norway	22.933° E and 79.427° N
Normal water	November 16, 2020	Virginia, USA	76.052° W and 36.999° N

Figure 2. The natural color images, grayscale images of remote sensing indices, and detection results of water quality anomalies. White represents the water quality anomalies, and black represents the non-water quality anomalies in the detection results.

Table 2. The precision, recall, and F1-scores of different water quality anomaly detection results.

Types	Index	Precision	Recall	F1-Score	Index	Precision	Recall	F1-Score
Water blooms	FAI	86.96%	97.30%	0.918	WAI	97.35%	95.83%	0.966
Green tides	EVI	62.79%	95.29%	0.757	WAI	85.71%	91.14%	0.883
Red tides	RI	80.98%	96.13%	0.879	WAI	86.52%	97.47%	0.917
Black and odorous water	BOI	32.24%	98.00%	0.485	WAI	91.84%	90.00%	0.909
Floods with light yellow	MNDWI	55.35%	100%	0.713	WAI	84.38%	95.07%	0.894
Floods with light green	NDWI	91.20%	95.89%	0.935	WAI	92.89%	96.19%	0.945
Oil spill	FI	84.91%	93.75%	0.891	WAI	88.79%	97.87%	0.920
Water pollution	WPDI	77.71%	90.21%	0.835	WAI	94.44%	97.84%	0.961

Figure 4. The natural color images, grayscale images of the WAI, and detection results of water quality anomalies. White represents the water quality anomalies, and black represents the non-water quality anomalies in the detection results.