基于EZW算法的叠前地震数据分频压缩技术

Frequency Division Compression Technology of Prestack Seismic Data Based on EZW Algorithm

随着高密度采集技术的发展及采集日效的大幅提高,勘探数据量呈指数增长。为了节省存储空间,提高传输效率,叠前地震数据的高保真压缩与重构研究显得极其迫切。嵌入式零树小波(embedded zerotree wavelet, EZW)算法具有优越的压缩性能,传统的EZW地震数据压缩基于t-x域(时间-空间域)数据。由于叠前地震数据的波数较宽,频带有限,经离散余弦变换(discrete cosine transform, DCT)后,能量主要集中在低频部分。本文提出一种分频地震数据压缩技术,通过2D-DCT将t-x域数据转换为DCT域数据并进行分频,对高频和低频数据单独进行EZW编码。低频数据编码级数高,保证重构数据的信噪比;高频数据编码级数低,提高数据的压缩比。模型数据和实际数据表明,在解压信噪比基本相当的情况下,分频地震数据压缩的压缩比高于常规EZW压缩方法。

With the significant improvement of high-density acquisition and daily acquisition efficiency,the amount of exploration data is growing exponentially.In order to save storage space and improve transmission efficiency,the research on high-fidelity compression and reconstruction of prestack seismic data is extremely urgent.EZW(embedded zerotree wavelet)algorithm has excellent compression performance.The traditional EZW algorithm for seismic data compression is based on data in the t-x domain.Because the wavenumber of prestack seismic data is wide and the frequency band is limited,the energy of the discrete cosine transform(DCT)data is mainly concentrated in the low-frequency in the DCT domain.This paper proposes a frequency division seismic data compression technology.Firstly,2D-DCT is performed on the t-x data,and then frequency division is applied to the 2D-DCT data to obtain high-frequency and low-frequency data.By separately coding high-frequency and low-frequency data based on EZW,the low-frequency data has a high coding level to ensure the signal-to-noise ratio(SNR)of the reconstructed data,and the high-frequency data has a low coding level to improve the data compression ratio(CR).The synthetic data and field data experiments show that the compression ratio with the proposed method is higher than that with the conventional EZW at the same SNR.