Analysis of the radiation pattern from Chirp SBP data

Chirp SBP(Sub-Bottom Profiler) is a marine high-resolution seismic systems. It uses a linear FM(Frequency modulated) pulse. It produces optimal penetration and vertical resolution because it uses frequencies typically covering the bandwidth 1-10 kHz. Chirp SBP has a transducer that generates source and acquires data reflected from the sub-bottom layer. This transducer has a radiation pattern related to its own angle. Therefore, it has different resolutions and behavioral characteristics in the acquired data. In this study, we apply the Chirp pulse to the staggered grid modeling method and generate Chirp data. We analyze the generated Chirp data by considering the radiation pattern. Also, we analyze characteristics of the radiation pattern by comparing the generated Chirp data to seismic physical modeling data. First, we set parameters of the Chirp pulse using the frequency, pulse length, etc. of commercial Chirp SBP acquisition systems. Then we generated Chirp data using the Chirp pulse and the 2-D staggered grid modeling method. Second, we derived the radiation pattern using the formula proposed Krautkr mer and Krautkr mer (1986) to calculate acoustic pressure at each angle from 30 to 60°, and acquired synthetic data through the radiation pattern. We analyzed the characteristics of the synthetic data at each angle. Finally, we compared the analyzed data to seismic physical modeling data in order to test the validity of the analyzed radiation pattern. Since the transducer used in the seismic physical modeling has a radiation pattern related to its own angle just like the transducer of Chirp SBP, we were able to acquire seismic physical modeling data by using the velocity model and survey acquisition parameters of the seismic numerical modeling. In this study, we analyzed characteristics of synthetic data at each angle of the radiation pattern using the Chirp pulse and the Chirp data generated through seismic numerical modeling. We also tested the validity of the data using seismic physical modeling. Based on numerical examples, we believe that Chirp SBP represents better resolutions when it uses the best radiation pattern through the analyzed data, and that it would be useful for researches that use transducers such as seismic physical modeling.