Is it possible to take incremental backup in MongoDB?
MongoDB doesn't provide an incremental backup option out of the box, but it's possible to do a file snapshot and replay the oplog.

As per MongoDB BOL Here If the volume where MongoDB stores its data files supports point-in-time snapshots, you can use these snapshots to create backups of a MongoDB system at an exact moment in time. File system snapshots are an operating system volume manager feature, and are not specific to MongoDB. With file system snapshots, the operating system takes a snapshot of the volume to use as a baseline for data backup. The mechanics of snapshots depend on the underlying storage system. 

For example, on Linux, the Logical Volume Manager (LVM) can create snapshots. 

For your further ref  Here and Here