Assessment of global geomagnetic models from aeromagnetic data in Cameroon, Central Africa

Figures & data

Figure 1. Geological reconstruction map of West African and NE Brazil Pan-African domains (Castaing et al. 1993). Cameroon borders are depicted as dashed lines and the aeromagnetic data used for comparison with the global geomagnetic models are represented by the red polygon. CCSZ: Central Cameroon Shear Zone; SF: Sanaga Fault; TBSZ: Tchollire Banyo shear zone; Pa: Patos shear zone; Pe: Pernambuco shear zone.

Table 1. Summary of the characteristics and performance metrics of the global geomagnetic models used in the study.

Data	Source provider	Altitude above geoid (km)	Resolution (arcmin)	Interpolation	Satellite base model	References
Emag2v2	GETECH	0 and 4	2	Directional gridding	MF6	Maus et al. (2009)
Emag2v3	GETECH	0 and 4	2	Kriging	MF7	Meyer et al. (2017)
WDMAM v2.0	GETECH	0 and 5	3	Near neighbor	CM4	Lesur et al. (2016)

Figure 2. Total magnetic intensity maps of Cameroon extracted from geomagnetic models with the 4 profiles used for comparison superimposed on each model: (a) EMAG2v2; (b) EMAG2V3; (c) WDMAM v2.0. We can observe similarities in the extension and intensity of the magnetic signal between both EMAG2v2 and WDMAM v2.0 models.

Figure 3. Aeromagnetic anomaly maps of: (a) Far North Cameroon with the two selected profiles (P₁ and P₂) superimposed on it; (b) part of the South region of Cameroun with the two selected profiles (P₃ and P₄) superimposed on it.

Table 2. Pearson’s correlation coefficient variation between EMAG2v3, EMAG2v2, WDMAM v2.0, and aeromagnetic data upward-continued at several heights for each profile.

	EMAG2v3	EMAG2v2	WDMAM v2.0	Up4km	Up5km	Up10km	Up15km	Up20km	Up25km	Up30km
Profile 1
Emag2v3	1	−0.148	−0.278	−0.1192	−0.1244	−0.142	−0.149	−0.148	−0.143	−0.136
Emag2v2	−0.148	1	0.951	0.9237	0.9304	0.950	0.958	0.960	0.959	0.956
WDMAM	−0.278	0.951	1	0.9173	0.9242	0.942	0.946	0.943	0.937	0.930
Up4km	−0.119	0.924	0.917	1	0.9995	0.989	0.974	0.959	0.947	0.936
Up5km	−0.124	0.930	0.924	0.9995	1	0.993	0.980	0.967	0.956	0.945
Up10km	−0.142	0.950	0.942	0.9887	0.9929	1	0.997	0.990	0.983	0.975
Up15km	−0.149	0.958	0.946	0.9738	0.9802	0.997	1	0.998	0.994	0.989
Up20km	−0.148	0.960	0.943	0.9595	0.9673	0.990	0.998	1	0.999	0.996
Up25km	−0.143	0.959	0.937	0.9469	0.9556	0.983	0.994	0.999	1	0.999
Up30km	−0.136	0.956	0.930	0.9360	0.9454	0.975	0.989	0.996	0.999	1
Profile 2
Emag2v3	1	−0.521	−0.888	−0.686	−0.703	−0.746	−0.740	−0.716	−0.688	−0.664
Emag2v2	−0.521	1	0.795	0.779	0.798	0.851	0.856	0.843	0.827	0.813
WDMAM	−0.888	0.795	1	0.823	0.843	0.891	0.884	0.858	0.829	0.804
Up4km	−0.686	0.779	0.823	1	0.998	0.954	0.885	0.824	0.776	0.741
Up5km	−0.703	0.798	0.843	0.998	1	0.969	0.910	0.854	0.809	0.776
Up10km	−0.746	0.851	0.891	0.954	0.969	1	0.984	0.954	0.925	0.902
Up15km	−0.740	0.856	0.884	0.885	0.910	0.984	1	0.992	0.978	0.964
Up20km	−0.716	0.843	0.858	0.824	0.854	0.954	0.992	1	0.996	0.989
Up25km	−0.688	0.827	0.829	0.776	0.809	0.925	0.978	0.996	1	0.998
Up30km	−0.664	0.813	0.804	0.741	0.776	0.902	0.964	0.989	0.998	1
Profile 3
Emag2v3	1	−0.399	−0.398	−0.435	−0.433	−0.421	−0.409	−0.399	−0.391	−0.385
Emag2v2	−0.399	1	0.989	0.993	0.996	0.991	0.974	0.956	0.939	0.924
WDMAM	−0.398	0.989	1	0.974	0.981	0.995	0.991	0.982	0.972	0.963
Up4km	−0.435	0.993	0.974	1	0.999	0.983	0.961	0.939	0.921	0.905
Up5km	−0.433	0.996	0.981	0.999	1	0.990	0.971	0.951	0.934	0.920
Up10km	−0.421	0.991	0.995	0.983	0.990	1	0.995	0.985	0.975	0.966
Up15km	−0.409	0.974	0.991	0.961	0.971	0.995	1	0.997	0.992	0.987
Up20km	−0.399	0.956	0.982	0.939	0.951	0.985	0.997	1	0.999	0.996
Up25km	−0.391	0.939	0.972	0.921	0.934	0.975	0.992	0.999	1	0.999
Up30km	−0.385	0.924	0.963	0.905	0.920	0.966	0.987	0.996	0.999	1
Profile 4
Emag2v3	1	−0.276	−0.1124	−0.234	−0.237	−0.236	−0.220	−0.207	−0.204	−0.220
Emag2v2	−0.276	1	0.9495	0.935	0.942	0.956	0.957	0.953	0.946	0.939
WDMAM	−0.112	0.949	1	0.935	0.944	0.966	0.976	0.980	0.980	0.975
Up4km	−0.234	0.935	0.9355	1	0.999	0.984	0.968	0.955	0.945	0.936
Up5km	−0.237	0.942	0.9439	0.999	1	0.990	0.978	0.966	0.957	0.949
Up10km	−0.236	0.956	0.9662	0.984	0.990	1	0.997	0.992	0.987	0.982
Up15km	−0.220	0.957	0.9758	0.968	0.978	0.997	1	0.999	0.996	0.993
Up20km	−0.207	0.953	0.9797	0.955	0.966	0.992	0.999	1	0.999	0.997
Up25km	−0.204	0.946	0.9796	0.945	0.957	0.987	0.996	0.999	1	0.999
Up30km	−0.220	0.939	0.9752	0.936	0.949	0.982	0.993	0.997	0.999	1

Table 3. Statistics for the amplitude difference and standard deviation between global geomagnetic models and aeromagnetic data for each profile. Up=Upward-continuation; TMI=Total Magnetic Intensity; Std.Dev= Standard deviation.

	TMI-EMAG2v2	Up15-EMAG2v2	Up20-EMAG2v2	TMI-EMAG2v3	Up15-EMAG2v3	Up20-EMAG2v3		TMI-WDMAM v2.0	Up15-WDMAM v2.0	Up20-WDMAM v2.0
Profile 1
Min (nT)	−114.20	−20.91	−21.54	−160.20	−71.90		−62.65	−95.60	−3.62	−4.24
Max (nT)	67.40	22.51	15.30	176.20	162.30		160.50	82.00	43.14	36.21
Mean (nT)	3.11	1.37	0.10	13.16	11.41		10.15	17.59	15.84	14.58
Std. Dev (nT)	35.86	10.20	8.70	82.28	66.11		63.46	37.26	11.72	10.10
Profile 2
Min (nT)	−128.40	−35.14	−25.52	−183.30	−91.74		−95.08	−106.30	−29.86	−18.98
Max (nT)	73.20	43.22	39.14	203.50	182.24		176.69	86.60	46.97	40.14
Mean (nT)	0.76	3.63	4.48	−12.13	−9.27		−8.41	10.99	13.85	14.71
Std. Dev (nT)	47.05	21.20	19.01	92.41	76.00		73.54	48.07	22.05	19.98
Profile 3
Min (nT)	−62.40	38.03	27.12	−235.20	−134.77		−91.98	−115.70	−15.27	21.72
Max (nT)	134.10	86.79	86.69	176.70	160.44		158.10	121.40	76.29	71.78
Mean (nT)	63.67	68.87	73.60	−1.49	3.72		8.45	38.98	44.18	48.91
Std. Dev (nT)	38.82	12.63	14.26	118.83	109.64		106.24	48.47	20.10	9.97
Profile 4
Min (nT)	−182.20	63.45	63.22	−323.40	−78.28		−60.79	−206.50	28.51	27.86
Max (nT)	166.50	111.16	130.44	159.50	80.62		70.06	149.90	73.27	78.17
Mean (nT)	37.03	83.96	88.70	−52.00	−5.07		−0.34	4.62	51.55	56.28
Std. Dev (nT)	77.43	13.88	18.52	119.86	53.89		44.15	78.87	9.87	13.83

Figure 4. Power density curves of both global geomagnetic models and aeromagnetic data of: (a) Far North Cameroon and (b) South Cameroon as depicted in Figure 1.

Figure 5. Comparison of EMAG2v2, EMAG2v3, WDMAM v2.0, and aeromagnetic data (extracted in Figs. 2 and 3) for each profile: (a) profile 1, a better match is observed between WDMAM v2.0, EMAG2v2 and 15-km, 20-km upward-continued airborne magnetic data respectively; (b) profile 2, a good correlation is found between WDMAM v2.0, EMAG2v2 and 10-km, 15-km upward-continued airborne magnetic data comprehensively; (c) profile 3, a strong correlation is noticeable between WDMAM v2.0, EMAG2v2 and 5-km, 10-km upward-continued airborne magnetic data respectively; (d) profile 4, a strong match is depicted between WDMAM v2.0, EMAG2v2 and 15-km, 20-km upward-continued airborne magnetic data comprehensively.

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Data availability statement

The data that support the findings of this study are available on request from the corresponding author. The aeromagnetic data are not publicly available due to some ethical restrictions.