The Mode-S Enhanced Surveillance (EHS) provides Air Traffic Control (ATC) more information than what is included in the Mode-S Elementary Surveillance (ELS).
There are quite a few very interesting data contained within various types of the EHS messages. Such as: airspeeds (IAS, TAS, Mach), roll angles, track angles, track angle rates, selected altitude, magnetic heading, vertical rate, etc.
There are a few challenges to decode this information:
Which aircraft does one message come from?
What is the type of one message (aka which BDS code) most likely to be?
How reliable is the information that has been decoded?