对比了两种先验模型融入方式,发现去归一化更高效准确。
Initial Model Incorporation for Deep Learning FWI: Pretraining or Denormalization?
- 用去归一化直接融合初始模型,无需预训练
- 去归一化使反演收敛更快、精度更高
- 适合追求高效反演的地球物理研究者
基于神经网络重参数化的全波形反演(FWI)已成为一种有效的无监督学习框架,可在初始模型不准确时稳定反演。其通过更新可训练的神经网络参数,而非直接微调地下模型。目前主要通过预训练和去归一化两种方式将初始模型先验知识融入神经网络。预训练需先拟合初始速度模型;去归一化则在无预训练情况下直接将网络输出叠加到初始模型上。本文系统研究了两种方法对神经网络重参数化FWI的影响。结果表明,预训练需在恒定速度值(均值)基础上进行模型扰动反演,采用两阶段实现,导致流程复杂且目标函数不一致,致使网络参数失活、失去可塑性。实验显示,去归一化可简化流程、加速收敛并提升反演精度。
原文摘要 · Abstract (English)
Subsurface property neural network reparameterized full waveform inversion (FWI) has emerged as an effective unsupervised learning framework, which can invert stably with an inaccurate starting model. It updates the trainable neural network parameters instead of fine-tuning on the subsurface model directly. There are primarily two ways to embed the prior knowledge of the initial model into neural networks, that is, pretraining and denormalization. Pretraining first regulates the neural networks' parameters by fitting the initial velocity model; Denormalization directly adds the outputs of the network into the initial models without pretraining. In this letter, we systematically investigate the influence of the two ways of initial model incorporation for the neural network reparameterized FWI. We demonstrate that pretraining requires inverting the model perturbation based on a constant velocity value (mean) with a two-stage implementation. It leads to a complex workflow and inconsistency of objective functions in the two-stage process, causing the network parameters to become inactive and lose plasticity. Experimental results demonstrate that denormalization can simplify workflows, accelerate convergence, and enhance inversion accuracy compared with pretraining.
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