Why is 的 needed in 二来是更深度的了解中国文化? In the following sentence:


  这次来中国，一来是提高中文水平，二来是更深度的了解中国文化。


The meaning should be something like the follows:


  The reason I came to China this time is, for one reason in order to raise my Chinese proficiency, and for another to understand the Chinese culture more deeply.


I also understand that 地 can be used to make the adjective work as an adverb. But this is 的, not 地. 

If I break down the components:


更深度的 - adverb? 
了解 - verb
中国文化 - object


I also understand 的 can make the adjective to a noun phrase, but in that case, it becomes a form of O-V-O, which doesn't make sense. 

So why is 的 needed in the sentence above and how does it work there?
The author used "的" incorrectly.

Obviously should use"地".