Remote sensing for detection and monitoring of vegetation affected by oil spills

Figures & data

Figure 1. The insert figure is the location of country/province/the Nigeria’s Niger Delta’ (image data false colour composite (bands 5, 4 and 3)), pipeline and oil spill sites.

Table 1. Information on oil spill data for the study site.

Sample SS	Latitude	Longitude	Date of spill	Date of image	Time (Days)	Quantity of oil spill in barrels (bbl)
SS1	6°5ʹ40.3ʹ’	5°32ʹ4.5ʹ’	13 December 2014	23 December 2014	10	108
SS2	5°33ʹ47.7ʹ’	5°35ʹ41.3ʹ’	25 November 2014	23 December 2014	28	5000
SS3	5°31ʹ8.8ʹ’	5°58ʹ40.6ʹ’	8 September 2014	23 December 2014	106	Na
SS4	5°33ʹ47.9ʹ’	5°35ʹ41.4ʹ’	6 September 2014	23 December 2014	108	60
SS5	5°56ʹ36.2ʹ’	5°54ʹ32.6ʹ’	1 September 2014	23 December 2014	113	1000
SS6	5°30ʹ.3.5ʹ’	5°57ʹ0.6ʹ’	20 August 2014	23 December 2014	125	3
SS7	5°32ʹ53.7ʹ’	5°52ʹ29.9ʹ’	n/a	23 December 2014	na	na
SS8	5°32ʹ47.3ʹ’	6°22ʹ1.5ʹ’	5 August 2014	23 December 2014	140	7.7
SS9	5°35ʹ27.2ʹ’	5°38ʹ58.8ʹ’	18 July 2014	23 December 2014	158	60

Figure 2. Box plot for the calculated mean of the 5 vegetation indices from (SS) and (NSS) sites for the 18 sample points each in 23 December 2014, where Q stands for quartile.

Figure 3. Oil spill sites (SS2 and SS4) detected by Landsat data (a & b) and NDVI (c & d) for 20 December 2013 and 23 December 2014.

Table 2. A comparison of p-value from paired t-test analysis for the study sites (SS and NSS sites) in 23 December 2014.

	Index	NDVI	SAVI	ARVI2	G-NIR	G-SWIR
SS vs NSS sites	p-value	***	***	***	**	*

****p-value < 0.0001, *** p-value < 0.005, ** p-value < 0.01, * p-value < 0.05, ^ns p-value ≥ 0.05.

Key: ****Highly significant, ***Highly significant, **Very significant, *Significant, ^nsNot significant.

Table 3. Analysis of change detection using paired t-test statistics of means of vegetation indices at the SS and NSS.

	20 December 2013(Pre-spill -Not polluted)		23 December 2014(Spill- date -Polluted)		10 January 2015(Post-spill -Not polluted)
	SS vs NSS		SS vs NSS		SS vs NSS
Index	Difference	p-value	Difference	p-value	Difference	p-value
NDVI	0.00	*	−0.08	***	−0.08	***
SAVI	0.05	*	−0.04	***	−0.05	**
ARVI2	−0.02	*	−0.09	***	−0.10	***
G-NIR	−0.02	*	−0.06	**	−0.06	**
G-SWIR	0.03	*	−0.09	*	−0.11	*

****p-value < 0.0001, *** p-value < 0.005, ** p-value < 0.01, * p-value < 0.05, ^ns p-value ≥ 0.05.

Key: ****Highly significant, ***Highly significant, **Very significant, *Significant, ^nsNot significant.

Table 4. shows the t-test analysis of the mean values for indices of vegetation affected by oil spill at the SS.

Index	2013 vs 2014		2014 vs 2015
	Change (Δ)	p-value	Change (Δ)	p-value
NDVI	−0.03	***	−0.03	*
SAVI	0.06	ns	−0.03	***
ARVI2	−0.04	***	0.04	*
G-NIR	−0.05	***	−0.02	**
G-SWIR	0.06	ns	−0.04	****

****p-value <0.0001, *** p-value <0.005, ** p-value <0.01, * p-value <0.05, ^ns p-value ≥ 0.05.

Key: ****Highly significant, ***Highly significant, **Very significant, *Significant, ^nsNot significant.

Figure 4. Oil spill sites (SS2 and SS4) detected in (b) Landsat data shown in Google Earth image of (a) February 2010, (c) June 2015 and (d) NDVI overlaid on 10 January 2015 Google image.