To acquire the field upgrades for the map, you will need to do a short side quest to unlock them.

The quest itself is pretty simple. Basically there are four grey chests around the map that has an AAT symbol written on it. One of them can be found next to the door leading from the Medbay, one is found in Spawn, one is found to the right of the Pack-A-Punch machine, and the final one is in the basement across from the code cylinder spawn location.

What you'll need to do to turn these chests into soulboxes to unlock the field upgrade is to get a weapon with the same AAT as is on the chest and knife it. Once done, the logo should start glowing and the chest will become a soulbox. Get kills using that same weapon until a fire starts appearing from the chest. Go up to it and you're able to buy a field upgrade.

Each AAT that can possibly spawn on a chest relates to one of the four field upgrades around the map.

Fireworks unlocks Frenzied Guard

Turned unlocks Toxic Growth

Blast Furnace unlocks the trustly ole Ring of Fire

Thunder Wall unlocks Aether Shroud.