# Influence of Source Shape on Semi-Airborne Transient Electromagnetic Surveys
## 3 Results
### Half-Space Model
#### 3.1.2 Magnetic Fields in the Air
Figure 8 presents the \(dB_{z}/dt\) distribution in the plane within the airborne receiving area at different time instants, with Figure 8a-c showing the curved source responses and Figure 8d-f displaying the linear source responses. The influence of the source geometry on \(dB_{z}/dt\) distribution exhibits patterns analogous to those observed in the \(B_{z}\) distribution. Both field components manifest as distinct anomalies in the proximal survey area during the early transient stage. Figure 6: \(B_{z}\) (A/m) in the plane within this airborne receiving area for the half-space model at different time instants. Panels (**a–c**) represent the curved source response, while panels (**d–f**) illustrate the linear source response. Figure 7: \(dB_{z}/dt\) (V/m\({}^{2}\)) of oxy plane in the air for the half-space model at different time instants. Panels (**a–c**) represent the curved source response, while panels (**d–f**) illustrate the linear source response. To further analyze these effects, we generated delay time profiles along survey lines at varying offsets. Delay time profiles are widely used to represent the transverse change characteristics of the responses [28]. Each line in the figure represents the observation data of different spatial positions at the same time, and the lines from top to bottom in the figure are correlated with the observation data from an early to a late time. Figure 9 presents the delay time profiles of \(B_{z}\) responses for both linear and curved sources at different offset distances. Figure 9a-c correspond to curved source responses at offsets of 200 m, 500 m, and 800 m, respectively, while Figure 9d-f correspond to linear source responses at identical offsets. The delay time profiles for linear sources exhibit parallel contours across all offset distances, whereas the profiles for curved sources display complex patterns. At an offset of y = \(-\)200 m, the multichannel profile of the curved source exhibits pronounced depressions and elevations. A direct interpretation of these curved source profiles using linear source response models would generate erroneous high- and low-resistivity anomalies in the shallow subsurface. At an offset of y = \(-\)500 m, the multichannel profile of the curved source displays partial undulations and tilting; however, the profile distortion is less severe compared to that observed at y = \(-\)200 m. Interpretation using linear source models would still produce false low-resistivity anomalies and tilted structures in the shallow subsurface. At an offset of y = \(-\)800 m, the multichannel profile of the curved source becomes virtually indistinguishable from that of the linear source, indicating that the influence of source curvature becomes negligible at this distance. Figure 10 presents the delay time profiles of \(dB_{z}/dt\) responses for both linear and curved sources at different offset distances. Figure 10a-c correspond to curved source responses at offsets of 200 m, 500 m, and 800 m, respectively, while Figure 10d-f correspond to linear source responses at the same offsets. Similarly, the effect of the source geometry on the multichannel profiles of \(dB_{z}/dt\) responses is consistent with the patterns observed in the \(B_{z}\) response profiles, confirming that both field components are affected in a comparable manner by the source geometry. Figure 8: \(dB_{z}/dt\) (V/m\({}^{2}\)) in the plane within this airborne receiving area for the half-space model at different time instants. Panels (**a–c**) represent the curved source response, while panels (**d–f**) illustrate the linear source response. Figure 10: Delay time profile of \(dB_{z}/dt\) (V/m\({}^{2}\)) at different offsets for half-space model. Panels (**a**-**c**) represent curved source response, and panels (**d**-**f**) are for linear source response. Figure 9: Delay time profile of \(B_{z}\) (A/m) at different offsets for half-space model. Panels (**a**-**c**) represent curved source response, and panels (**d**-**f**) illustrate linear source response.