Figure 1
Location and Data availability of geomagnetic observations operated by Indian Institute of Geomagnetism. Station code abbreviations are included in Table 1.
Table 1
Location of geomagnetic observatories in India with station name, IAGA observatory code, type of instruments.
| S.NO. | MAGNETIC OBSERVATORY | IAGA CODE | INSTRUMENT TYPE | GEOGRAPHIC | GEOMAGNETIC |
|---|---|---|---|---|---|
| LATITUDE(N) LONGITUDE(E) | LATITUDE(N) LONGITUDE(E) | ||||
| 1. | Tirunelveli | TIR | Izmiran, DFM | 8° 42’ 77° 48’ | 0.15° 150.71° |
| 2. | Port Blair | PBR | DFM | 11° 48’ 92° 43’ | 2.28° 165.56° |
| 3. | Pondichery | PND | Izmiran, DFM | 11° 55’ 79° 55’ | 3.16° 153.05° |
| 4. | Visakhapatnam | VSK | Izmiran, DFM | 17° 41’ 83° 19’ | 8.64° 156.77° |
| 5. | Alibag | ABG | Izmiran, DFM | 18° 37’ 72° 52’ | 10.40° 146.81° |
| 6. | Nagpur | NGP | Izmiran, DFM | 21° 09’ 79° 05’ | 12.38° 152.99° |
| 7. | Rajkot | RKT | DFM | 22° 18’ 76° 47’ | 13.70° 150.90° |
| 8. | Silchar | SIL | Izmiran, DFM | 24° 56’ 92° 49’ | 15.33° 166.23° |
| 9. | Allahabad (Renamed as prayagRaj) | ALH | DFM | 25° 27’ 81° 51’ | 16.44° 155.96° |
| 10. | Shillong | SHL | Izmiran, DFM | 25° 34’ 91° 53’ | 16.00° 165.39° |
| 11. | Jaipur | JAI | Izmiran, DFM | 26° 55’ 75° 48’ | 18.36° 150.41° |
| 12. | Gulmarg | GUL | Izmiran, DFM | 34° 05’ 74° 24’ | 25.59° 149.87° |
Figure 2
Typical example showing the data spikes in Z component of Alibag (ABG) observatory for 2011 and the corrected Z component values. (a) Unprocessed data set; (b) processed data set.
Table 2
Details of Data corrections and status of data for all stations used in this study. IAGA code is same as used in Table 1.
| IAGA CODE | BEFORE PROCESSING | SD (nT) | AFTER PROCESSING | SD (nT) | ||
|---|---|---|---|---|---|---|
| MIN (nT) | MAX (nT) | MIN (nT) | MAX (nT) | |||
| TIR | 1052 | 2499 | 289.6 | 1387 | 2438 | 289.6 |
| PND | 7500 | 8727 | 259.5 | 7708 | 8727 | 258.3 |
| VSK | 6501 | 18301 | 599.6 | 17080 | 18301 | 357.7 |
| ABG | 19000 | 20488 | 302.5 | 19412 | 20488 | 301 |
| NGP | 22000 | 23261 | 295.6 | 22202 | 23261 | 293.2 |
| RKT | 23001 | 24819 | 177.8 | 24190 | 24819 | 171.4 |
| SIL | 19001 | 29676 | 327.8 | 28625 | 29676 | 293 |
| ALH | 29000 | 32220 | 328.3 | 29367 | 30220 | 249 |
| SHL | 28001 | 30641 | 561.2 | 29261 | 30641 | 429.9 |
| JAI | 30500 | 31861 | 285.6 | 30797 | 31861 | 283.5 |
| GUL | 39500 | 40840 | 356.6 | 39648 | 40840 | 356.3 |
Figure 3
Results of different spatial interpolation method to get the magnetic field variation for Z component, over Indian region using IIG network for the year 2020.
Table 3
Statistical parameters for all the interpolation methods applied to magnetic field daily averaged data for the year 2020 (Z component).
| S.NO | INTERPOLATION METHOD | MIN (nT) | MAX (nT) | MEAN (nT) | S.D (nT) |
|---|---|---|---|---|---|
| 1 | Inverse distance to Power (INV) | 2375.374 | 40240.05 | 23981.01 | 6207.401 |
| 2 | Kriging (KRG) | 2906.175 | 39828.85 | 24631.17 | 7823.3 |
| 3 | Local Polynomial (LCP) | 4751.477 | 38744.21 | 23890.17 | 7643.955 |
| 4 | Minimum Curvature (MNC) | 2494.816 | 39893.56 | 24764.51 | 7998.209 |
| 5 | Modified Shepard’s Method (MSM) | 2961.5 | 40127.42 | 24826.6 | 7954.926 |
| 6 | Moving Average (MOA) | 17901.8 | 28798.71 | 23474.56 | 2366.748 |
| 7 | Natural Neighbor (NAN) | 3849.987 | 39839.23 | 24603.49 | 7722.897 |
| 8 | Nearest Neighbor (NEN) | 2027.8 | 40458 | 24381.98 | 8224.504 |
| 9 | Polynomial Regression (POR) | 4202.033 | 41453.94 | 24562.46 | 8041.312 |
| 10 | Radial Basis Function (RBF) | 2641.434 | 40067.2 | 24721.98 | 7947.856 |
| 11 | Triangulation With Linear Interpolation (TLP) | 2886.523 | 39851.7 | 24603.15 | 7892.121 |
Table 4
Difference between observed and interpolated values (nT) of Z component (1 day averaged data for Jan 1st, 2015) after removing one by one station.
| METHODS | KRG | NAN | NEN | IDW | RBF | POR | TLP | MSM | MNC | MOA | LCP |
|---|---|---|---|---|---|---|---|---|---|---|---|
| NAG | 1.36E+03 | 1.23E+03 | –167 | 9.13E+02 | 1.30E+03 | 1.60E+03 | 1.06E+03 | 8.95E+02 | 8.15E+02 | –1.29E+02 | 2.40E+02 |
| POND | 1.51E+03 | –4.25E+37 | 6.25E+03 | –1.70E+38 | 2.36E+03 | 6.98E+02 | –4.25E+37 | 2.21E+03 | 3.02E+03 | –1.23E+04 | –1.70E+38 |
| SHL | –1.71E+03 | –1.70E+38 | –895 | –2.42E+02 | –2.04E+03 | –1.99E+03 | –1.28E+38 | –3.58E+03 | –3.80E+03 | 3.04E+03 | –3.01E+03 |
| ALA | 1.16E+03 | 6.91E+02 | 4.81E+03 | –1.70E+38 | 1.62E+03 | 3.57E+02 | 4.15E+02 | 7.78E+02 | 1.04E+02 | 5.83E+03 | 2.15E+02 |
| AIL | 9.80E+02 | –8.50E+37 | –4577 | 1.93E+03 | 1.11E+03 | 1.93E+03 | –4.25E+37 | –2.51E+02 | –2.51E+02 | –1.86E+03 | 1.29E+03 |
| VSK | –2.40E+03 | –1.35E+03 | –6616 | –4.67E+03 | –2.69E+03 | –1.13E+03 | –1.39E+03 | –1.74E+03 | –4.03E+02 | –5.59E+03 | –9.62E+02 |
| JAI | 3.77E+02 | –1.70E+38 | 0 | –1.70E+38 | 6.00E+01 | –1.82E+03 | –1.70E+38 | –1.54E+02 | –5.20E+02 | 1.25E+04 | –3.72E+01 |
| SIL | 2.62E+03 | –1.70E+38 | 895 | 1.52E+03 | 3.13E+03 | 3.13E+03 | –1.70E+38 | 4.06E+03 | 3.42E+03 | 4.87E+03 | 3.45E+03 |
| GUL | 3.99E+02 | –5.67E+37 | 0 | 9.71E+02 | 2.13E+02 | 60.31 | –5.67E+37 | –2.81E+02 | –1.50E+02 | 5.76E+03 | –1.58E+02 |
| RKT | NaN | NaN | NaN | NaN | NaN | NaN | NaN | NaN | NaN | NaN | NaN |
| TIR | NaN | NaN | NaN | NaN | NaN | NaN | NaN | NaN | NaN | NaN | NaN |
| Average | 4.77E+02 | –7.71E+37 | –3.33E+01 | –5.67E+37 | 5.63E+02 | 3.15E+02 | –6.77E+37 | 2.15E+02 | 2.48E+02 | 1.35E+03 | –1.89E+37 |
Table 5
RMSE For 1-day averaged data (Jan 1st, 2015) for 11 different methods at 11 observatories.
| OBS. | KRG | NAN | NEN | IDW | RBF | POR | TLP | MSM | MNC | MOA | LCP |
|---|---|---|---|---|---|---|---|---|---|---|---|
| TIR | 708.9 | 1.70E+38 | 0 | 732.1 | 1458.2 | 1331.3 | 1.70E+38 | 85.04 | 658.1 | 13635.2 | 75.5 |
| PND | 1842.3 | 8.51E+37 | 0 | 825.0 | 1640.9 | 1578.9 | 8.51E+37 | 2013.4 | 2423.9 | 10717.7 | 2102.8 |
| VSK | 565.9 | 632.8228 | 0 | 760.4 | 1543.2 | 962.9 | 690.9 | 284.5 | 519.6 | 5031.4 | 108.0 |
| ABG | 1356.6 | 1.20E+38 | 0 | 502.2 | 1547.4 | 2066.3 | 8.51E+37 | 1244.7 | 1300.6 | 1657.7 | 1397.7 |
| NGP | 1998.9 | 1894.744 | 0 | 656.3 | 1698.3 | 2074.9 | 1875.3 | 1824.8 | 1819.7 | 117.5 | 1935.8 |
| RKT | 1151.6 | 1.70E+38 | 0 | 214.3 | 1289.0 | 1511.4 | 1.70E+38 | 1084.3 | 1105.9 | 2919.2 | 1207.2 |
| SIL | 1392.2 | 1.70E+38 | 0 | 458.3 | 385.8 | 2619.7 | 1.70E+38 | 284.9 | 2636.7 | 3879.6 | 1274.2 |
| ALH | 1120.5 | 1106.886 | 0 | 993.7 | 1420.2 | 1394.2 | 1119.3 | 1670.2 | 1689.8 | 5340.6 | 1469.6 |
| SHL | 989.3 | 1.47E+38 | 447.5 | 406.2 | 736.8 | 1976.7 | 1.47E+38 | 612.1 | 3499.0 | 2523.5 | 793.2 |
| JAI | 1532.3 | 1462.13 | 0 | 867.2 | 1385.5 | 1637.3 | 1475.0 | 1743.4 | 1751.3 | 5693.8 | 1445.6 |
| GUL | 379.2 | 1.70E+38 | 0 | 617.4 | 870.5 | 1947.0 | 1.70E+38 | 426.9 | 739.3 | 11869.5 | 64.5 |
| Average RMSE over all stations | 1185.24 | 9.38E+37 | 447.5 | 639.37 | 1270.53 | 1736.42 | 9.07E+37 | 1025 | 1649.45 | 5762.34 | 1079.46 |
Figure 4
Snapshot of MATLAB based GUI for obtaining the interpolated contour for H and Z magnetic field components.
Figure 5
Gridded magnetic field components (a) H and (b) Z for the year 2011.
Figure 6
Variations of total H and interpolated and observed Z field components for the years 2011–2020, created using MATLAB GUI. Panels (a), indicate the monthly variation of interpolated (dashed lines) and observed (solid lines) Z values for entire India. Panels (b) and (c) indicate the observed values of Z field at TIR and ABG respectively in minute resolution during 2011–2020. Panel (f) shows the variation of interpolated Z field at ABG location during 2011–2020.