Syntax: WBADMIN START SYSTEMSTATEBACKUP -backupTarget: -quiet Description: Creates a system state backup of the local computer ...

Syntax: WBADMIN START SYSTEMSTATEBACKUP
    -backupTarget:
    [-quiet]

Description:  Creates a system state backup of the local computer and stores 
it on the location specified.
To use this command, you must be a member of the Backup Operators group 
or Administrators group. 

Parameters:
-backupTarget  Specifies the location where you want to store the backup. 
                The storage location requires a drive letter or a GUID-based 
                volume of the format: \\?\Volume{GUID}.

-quiet         Runs the command with no prompts to the user.

Example: 
WBADMIN START SYSTEMSTATEBACKUP -backupTarget:f: