documentclass{article}

usepackage[utf8]{inputenc}
usepackage{graphicx}
usepackage{subcaption}

begin{document}
begin{figure*}

   hspace*{-1.1in}
    begin{subfigure}[b]{textwidth}
        centering
        includegraphics[scale=0.37]{dummy.jpg}
        caption{small a image }
        label{fig:subfigure1}
    end{subfigure}
    vskipbaselineskip
    hspace*{-1.1in}
    begin{subfigure}[b]{textwidth}
        centering
        includegraphics[scale=0.37]{dummy.jpg}
        caption[]%
        {{small b image}}
        label{fig:subfigure2}
    end{subfigure}
    vskipbaselineskip
    hspace*{-1.1in}
    begin{subfigure}[b]{textwidth}
        centering
        includegraphics[scale=0.37]{dummy.jpg}
        caption[]%
        {{small c image}}
        label{fig:subfigure3}
    end{subfigure}

    caption[ whole image caption here]
    {small whole image caption here}
    label{fig:experiments}
end{figure*}

end{document}