## 2 Data and Results
Simultaneous scalar-F measurements are also carried out during the period of D/I observations, from which the absolute values of the H, D and Z components are derived. Figure 3 shows the absolute values of D, I and F from February 2020 to May 2020. The red color depicts the spot values from before lockdown and the green color depicts those during lockdown. Some variations in spot values can be ascribed to the different times of day at which measurements were performed. Overall, the I and F spot values are more consistent compared to D. Scatter between the absolute measurements of D, I and F carried out on the same day ranges from 0.05 to 0.5 min, 0.03 to  
Figure 2: Shows the first difference (the approximate derivative) of 1s measurements of Z and F components. (**a**) Z component on 11 March 2020 (before lockdown), (**b**) Z component on 6 April 2020 (during lockdown), (**c**) F component on 11 March 2020 (before lockdown) and (**d**) F component on 6 April 2020 (during lockdown). 0.1 min and 0.6 to 3.6 nT, respectively, before lockdown, and 0.07 to 0.6 min, 0.02 to 0.5 min and 0.6 to 2.1 nT during lockdown. These absolute measurements were used to calculate the baselines of H, D and Z, which are necessary to prepare definitive data of the geomagnetic field components. Having assessed the amplitudes of noise in the variation data and absolute measurements of D and I, we checked the effect on the calculated baselines (only for 86 days, including the lockdown period). These baselines were processed by only considering those spot values of absolute and variation data, which are consistent and devoid of noise, and excluding data points that have high noise levels during the period of observation. In Figure 4, the left side (red) portion indicates the baselines of H, D and Z before lockdown and the right side (green) is during the lockdown period. Over the observation period (45 days), the baseline variation range was about 0.6 nT, 0.06 min and 0.4 nT in the H, D and Z components, respectively, before lockdown. During the period of lockdown (42 days), the corresponding values changed slightly to 0.4 nT, 0.05 min and 0.8 nT, respectively. The standard deviations of measurements from the calculated baselines reduced by 25-50% in the different components during the lockdown period, compared to normal traffic conditions, as shown in Table 1. The averages of the differences in amplitudes between consecutive values of calculated baselines for each day of absolute measurement were 0.29 nT, 0.05 min and 0.13 nT for H\({}_{\text{B}}\), D\({}_{\text{B}}\) and Z\({}_{\text{B}}\) before lockdown, and 0.24, 0.03 and 0.17 during lockdown, showing that the baselines were undisturbed by the vehicular noise, as shown in Table 2. \begin{table}
\begin{tabular}{l l l} \hline  & **HYB** & **CPL** \\ \hline Established on & 1965 by CSIR-NGRI & 2012 by CSIR-NGRI \\ \hline Geographic Latitude & 17\({}^{\circ}\)25.0\({}^{\prime}\) N & 17\({}^{\circ}\)17.6\({}^{\prime}\) N \\ \hline Geographic Longitude & 78\({}^{\circ}\)33.0\({}^{\prime}\) E & 78\({}^{\circ}\)55.2\({}^{\prime}\) E \\ \hline Geomagnetic dipole Latitude & 09\({}^{\circ}\)00.0\({}^{\prime}\) N & 08\({}^{\circ}\)49.2\({}^{\prime}\) N \\ \hline \end{tabular}
\end{table} 
Table 1: Details of geographic and geomagnetic dipole coordinates (GDC) of the HYB and CPL Observatories used in the study. Figure 3: Absolute values of D, I and F components before (7 February 2020 to 18 March 2020, red color symbols) and during (27 March 2020 to 4 May 2020, green color symbols) the lockdown period, with annotation of dates of observations and K-index value during the time the observations were conducted.