From Halopedia, the Halo wiki
While on their mission the ship intercepted Covenant transmissions about an imminent attack on the UNSC colony Troy (Sorenson had actually been based on Troy). Greene was forced to make a decision to either give forewarning to the colony, allowing them to evacuate while tipping off the Covenant that their communication codes had been broken, or let the Covenant attack, thus maintaining the ability to listen in on Covenant com channels.
Her decision is played through Melissa's eyes in the flashback scenes when the SPDR is rebuilding Melissa and can be read in the Phase 2 Operator's Monologue. The following conversation was observed by Melissa between First Lieutenant Rolf Sorenson and Captain Greene. It is one of a few times Sorenson is mentioned
Part of the Phase 2 Operator's Monologue
1st Lt Sorenson: Oh my God. If the decrypt is right— Capt. Greene: I know. 1st Lt Sorenson: We have to /// drop the mission.... An evac on this scale they need every second. ...Jesus. Capt. Greene: I'm not... I'm not sure. 1st Lt Sorenson: The mission... This mission is more important than millions of lives? Oh my... /// god. Capt. Greene: I'm just saying, the choice isn't as easy as you might think. Capt. Greene: ...If they act, they risk letting the enemy know we have a toehold in their /// C-and-C. If they decide that strategic advantage is too great to risk and don't act, then you know Section Zero will be all over them. Zero's wanted Standish forever. 1st Lt Sorenson: I...I understand. It's so much easier for everyone if we don't tell them. But...wait a second. Don't you have family on Troy? Capt. Greene: That can't be part of the equation, Rolf. You know that. 1st Lt Sorenson: Jesus.
The only other time Sorenson is mentioned is in the Phase 3 Memories flashbacks when it was revealed that Sorenson donned a space suit and closely inspected the Covenant artifact brought onboard the Apocalypso.