Latex: How to avoid omitting the author's name when citing two references with the same name author in the same position

Question

I cite 2 references via \citep{liu2007cast,liu2011shadow} command, and it style (after compiled) is:

In [Liu et al., 2011, 2007], the lower intensity rule is used as a preclassier in their method.

But my desired style is:

In [Liu et al. 2011, Liu et al. 2007], the lower intensity rule is used as a preclassier in their method.

As shown in the ref.bib, the names of the two authors are not exactly the same. But the author of the second reference was omitted by default.

sample of my book.tex

\documentclass[a4paper,12pt]{article}
\usepackage{amsmath}
\usepackage{graphicx}
\usepackage{float}
\usepackage[semicolon,square,sort&compress,sectionbib]{natbib}
\renewcommand\theequation{\arabic{section}-\arabic{equation}}
\renewcommand\thefigure{\arabic{section}-\arabic{figure}}
\title{In nature}
\author{Null}
\date{}

\begin{document}
In \citep{liu2007cast,liu2011shadow}, the lower intensity rule is used as a preclassifier in their method. 
\bibliographystyle{abbrvnat}
\bibliography{ref}
\end{document}

sample of my ref.bib

@inproceedings{liu2007cast,
  title={Cast shadow removal combining local and global features},
  author={Liu, Zhou and Huang, Kaiqi and Tan, Tieniu and Wang, Liangsheng},
  booktitle={2007 IEEE Conference on Computer Vision and Pattern Recognition},
  pages={1--8},
  year={2007},
  organization={IEEE}
}
@article{liu2011shadow,
  title={Shadow detection in remotely sensed images based on self-adaptive feature selection},
  author={Liu, Jiahang and Fang, Tao and Li, Deren},
  journal={IEEE Transactions on Geoscience and Remote Sensing},
  volume={49},
  number={12},
  pages={5092--5103},
  year={2011},
  publisher={IEEE}
}

Answer 1

You could use the \citep* macro:

\documentclass[a4paper,12pt]{article}
\usepackage{amsmath}
\usepackage{graphicx}
\usepackage{float}
\usepackage[semicolon,square,sectionbib,sort&compress,mcite]{natbib}
\renewcommand\theequation{\arabic{section}-\arabic{equation}}
\renewcommand\thefigure{\arabic{section}-\arabic{figure}}
\title{In nature}
\author{Null}
\date{}

\begin{filecontents*}[overwrite]{\jobname.bib}
@inproceedings{liu2007cast,
  title={Cast shadow removal combining local and global features},
  author={Liu, Zhou and Huang, Kaiqi and Tan, Tieniu and Wang, Liangsheng},
  booktitle={2007 IEEE Conference on Computer Vision and Pattern Recognition},
  pages={1--8},
  year={2007},
  organization={IEEE}
}
@article{liu2011shadow,
  title={Shadow detection in remotely sensed images based on self-adaptive feature selection},
  author={Liu, Jiahang and Fang, Tao and Li, Deren},
  journal={IEEE Transactions on Geoscience and Remote Sensing},
  volume={49},
  number={12},
  pages={5092--5103},
  year={2011},
  publisher={IEEE}
}
\end{filecontents*}

\begin{document}
In \citep*{liu2007cast,liu2011shadow}, the lower intensity rule is used as a preclassifier in their method. 
\bibliographystyle{abbrvnat}
\bibliography{\jobname}
\end{document}