Mapping of ferric (Fe³⁺) and ferrous (Fe²⁺) iron oxides distribution using ASTER and Landsat 8 OLI data, in Negash Lateritic iron deposit, Northern Ethiopia

Figures & data

Figure 1. Location map of the study area.

Figure 2. Geological map of Negash area.

Table 1. Performance characteristics of satellite data.

Data set	Band name	Band width (µm)	Spatial resolution (m)	Acquisition date	Source
ASTER	1 VIS	0.52 − 0.60	15	Dec 10, 2005	http://earthexplorer.usgs.gov/
	2 VIS	0.63 − 0.69	15
	3 N NIR	0.78 − 0.86	15
	4 SWIR	1.600 − 1.700	30
	5 SWIR	2.145 − 2.185	30
	6 SWIR	2.185 − 2.225	30
	7 SWIR	2.235 − 2.285	30
	8 SWIR	2.295 − 2.365	30
	9 SWIR	2.360 − 2.430	30
Landsat 8 OLI	Band 2 – Blue	0.45 − 0.51	30	28 January 2020	https://glovis.usgs.gov/
	Band 3 – Green	0.53 − 0.59	30
	Band 4 – Red	0.64 − 0.67	30
	Band 5− Near infrared	0.85 − 0.88	30
	Band 6− SWIR 1	1.57 − 1.65	30
	Band 7− SWIR 2	2.11 − 2.29	30

Figure 3. Flowchart of the Methodology.

Figure 4. NDVI map generated from Landsat 8 OLI (a), and ASTER (b).

Table 2. Threshold, confidence level and area mapped using all techniques.

Sensor	Technique	Confidence level	Threshold used	Area in (km^2)
ASTER	Band 2/1	92%	222.8	62.1
	Band 5/3 + 1/2	92%	220	56.8
	Band 4/5	92%	210	57.8
	Selective PCA	95%	210.5	34.79
	Unmixing (goethite)	92%	197	8.4
	Unmixing (hematite)	98%	185	26.5
	Goethite MF			16.4
	Hematite MF			52
Landsat 8 OLI	Band 6/4	95%	197.2	13.75
	Band 4/3	95%	188	13.2
	Selective PCA	95%	214.2	32.5
	MF (goethite)			28.4
	MF (hematite)			14.8

Figure 5. Ferrous iron anomaly map generated from Landsat 8 OLI (a), ASTER (b), and ferric iron anomaly generated from Landsat 8 OLI (c), and ASTER (d).

Figure 6. Laterite anomaly map generated from ASTER band ratio (a), anomaly map generated from PC4 Landsat 8 OLI (b), ASTER PC4 (c), and (d) final endmembers extracted from (a) ASTER, and (b) Landsat 8 OLI.

Table 3. ASTER bands 1, 2, 3 and 4 eigenvector loadings.

Eigenvectors	Band 1	Band 2	Band 3	Band 4
PC 1	−0.332	−0.473	−0.515	−0.634
PC 2	−0.428	−0.512	−0.152	0.729
PC 3	0.267	0.39	−0.844	0.254
PC 4	0.797	−0.602	−0.013	0.042

Table 4. Landsat bands 2, 4, 5 and 6 eigenvector loadings.

Eigenvectors	Band 2	Band 4	Band 5	Band 6
PC 1	0.189	0.443	0.492	0.725
PC 2	−0.365	−0.468	−0.436	0.677
PC 3	−0.323	−0.567	0.753	−0.08
PC 4	0.853	−0.513	−0.010	0.098

Table 5. MNF eigen values of ASTER and Landsat 8 OLI.

Eigenvalues
ASTER		Landsat 8 OLI
MNF 1	57.2	MNF 1	16.1
MNF 2	29.3	MNF 2	7.8
MNF 3	11.1	MNF 3	6.4
MNF 4	8.2	MNF 4	5.8
MNF 5	6.2	MNF 5	3.4
MNF 6	5.8	MNF 6	1.99
MNF 7	3.8
MNF 8	3.3
MNF 9	2.6

Table 6. Unknown and reference spectral curve matching values of ASTER.

n-D class mean	SFF value	Matched known mineral
1	0	No matching mineral
2	0.95	Topaz
3	0.81	Goethite
4	0.96	Alunite
5	0.99	Topaz 2
6	0	No matching mineral
7	0.77	Lepidolite
8	0.85	Hematite
9	0.97	Pyrophyllite
10	0.82	Hornblende

Table 7. Unknown and reference spectral curves matching values of Landsat 8 OLI.

n-D class mean	SFF	Matched mineral
1	1	Goethite
2	1	Kaolin
3	1	Hematite
4	1	Alunite
5	0	No matching mineral
6	1	Wollastonite
7	0	No matching mineral

Figure 7. ASTER unmixing (a) Goethite anomaly and (b) Hematite anomaly, and scatter plots showing high MF and low infeasibility goethite and hematite of ASTER (c), and Landsat 8 OLI (d).

Figure 8. ASTER MTMF (a), Goethite anomaly and (b) Hematite anomaly and Landsat 8 OLI MTMF (c) Goethite anomaly and (d) Hematite anomaly.

Figure 9. Graphs showing correlation b/n results obtained from pixel-level image processing of Landsat 8 OLI and ASTER (a) and correlation b/n results obtained from Landsat OLI, and ASTER MTMF (b).

Figure 10. Ratio of anomalous areas overlay on polygons of the existing iron oxides (a), and selective PCA results overlay with existing iron oxide polygons (b).

Figure 11. Unmixing and MTMF results overlay on existing iron oxide polygons.