Meaning of this definition of 落雷?


> 落雷:雷が落ちること。 **地表物を一つの電極とした** 雷雲からの放電現象。[季]夏。

I can't understand the meaning of the bold part.  
I looked up 地表物 but could find nothing.




  * 地表 = the surface of the ground
  * 物 = stuff/objects
  * 地表 + 物 = objects on the surface of the ground
  * 電極 = electrodes

So the whole thing would be something like,

[code]

    A phenomena of electrical discharge（放電現象）
    from a storm cloud（雷雲から）
    whereby（とした）
    an object on the surface of the ground（地表物）
    becomes（とした）
    one of the electrodes（一つの電極）
    
[/code]

Or...

> A phenomenon whereby an object on the surface of the ground becomes one of
> the electrodes in an electrical discharge from a storm cloud.




  * 地表 = the surface of the ground
  * 物 = stuff/objects
  * 地表 + 物 = objects on the surface of the ground
  * 電極 = electrodes

So the whole thing would be something like,

[code]

    A phenomena of electrical discharge（放電現象）
    from a storm cloud（雷雲から）
    whereby（とした）
    an object on the surface of the ground（地表物）
    becomes（とした）
    one of the electrodes（一つの電極）
    
[/code]

Or...

> A phenomenon whereby an object on the surface of the ground becomes one of
> the electrodes in an electrical discharge from a storm cloud.

