# reason for np.log here is the theta is log-transformed hyperparameters (https://github.com/scikit-learn/scikit-learn/blob/5491dc695/sklearn/gaussian_process/kernels.py#L1531) line (289)
ax.contour(Theta0,Theta1,LML,levels=200)
ax.contour(Theta0,Theta1,LML,levels=1000)
# find optimized theta0, theta1, using the above contour as guidanve