What is the difference between ADS-B UAT and ADS-B ES?
ADS-B UAT operates on 978 MHz and are available for aircraft that operate below 18,000 FT MSL.  UAT transceivers can display aviation weather products (FIS-B) as well as traffic from ground radio stations (TIS-B).  The airplane must be in a coverage area for TIS-B services.


  TIS-B is intended to provide ADS-B equipped aircraft with a more complete traffic picture in situations where not all nearby aircraft are equipped with ADS-B Out. - AIM 4-5-8


Aviation weather products available over FIS-B through ADS-B UAT transceivers




ADS-B 1090ES operates on 1090 MHz and is required for aircraft operating above 18,000 FT MSL.  The information sent over a Mode S transponder is greater and is called an "extended squitter".  These aircraft will be able to display traffic directly from other ADS-B equipped aircraft and those with Mode S transponders without the need to rely on ground based systems.  FIS-B is not available to these transceivers.



The picture below illustrates where 1090ES and UAT are allowed / required for aircraft after the ADS-B mandate in 2020.





References:


Aeronautical Information Manual 4-5-7 thru 4-5-9
Advisory Circular 90-114A