the ending "sen" in Danish just means "son of". So Sorensen basically means the son of Soren. You see this in many languages, think about "Johnson" or "Jakobson" in English/American.
right now if I could only get half of my credit cards to recognize that its the danish version "sen" instead of "son". I have called to change my discover 3 times. Each time the new card arives spelled the same.....