Source signature and static shifts estimations for multi-component ocean bottom data

Ocean Bottom Nodes dataset

The P (pressure) and Z (vertical velocity) components of an ocean bottom common receiver gather are shown in Figures 2. Data are acquired using ocean bottom nodes. The typical water depth in the surveyed area is around 500m with a soft sediment layer of 150m. From the raw data, we can identify direct arrivals, refraction, and water reverberations. There is an outcrop at the sea bottom to the left of the ocean bottom node (OBN) receiver. The dataset is spatially aliased, with 50 meters spacing between shots.

PZdata
Figure 2. The left plot shows the pressure component and the right plot shows the vertical velocity component. From the raw data, we can identify direct arrivals, refraction, and water reverberations.[ER]

To focus on the source signal, we apply hyperbolic moveout (HMO) at a velocity of $1480$m/s and time-window the data near the direct arrival (Figure 3). Linear moveout performs time-shifting ( $\Delta \tau$) on each trace. Time shifts are offset-dependent and are calculated as shown in equation 1:

HMOraw
Figure 3. The top plot shows the pressure component and the bottom plot shows the vertical velocity component after hyperbolic moveout correction. The data are time-windowed around direct arrival.[ER]

$$\Delta \tau = \sqrt{\tau_o^2 + \frac{x^2}{v^2}} - \tau_o ,$$ (1)

where $x$ is the full offset, $v$ is the water velocity, and $\tau_o$ is the zero-offset arrival time. From Figure 3, we can see that the direct arrival is not perfectly flat. This non-flatness indicates shot statics in this common-reciever gather. Shot statics can be caused by variations in deployment depth and cross-line displacement. Another noticeable feature is that primary reflections follow almost immediately after the direct arrivals. This causes difficulty, as primary signal would overlap with the source bubble signal. Next, we present two methods to estimate the source statics by flattening the HMO output.

Source signature and static shifts estimations for multi-component ocean bottom data