A system, comprising: an exhaust aftertreatment system configured to treat emissions from a combustion engine, wherein the exhaust aftertreatment system comprises: a selective catalytic reduction SCR catalyst assembly configured to receive a fluid from the combustion engine, wherein the SCR catalyst assembly has an inlet and an outlet; at least one radio frequency RF probe disposed within the SCR catalyst and configured to measure ammonia NH 3 storage of the SCR catalyst; an injection system configured to inject NH 3 or urea into the fluid upstream of the inlet of the SCR catalyst; a controller communicatively coupled to the exhaust aftertreatment system, wherein the controller is configured to control operations of the exhaust aftertreatment system and to receive signals representative of the measured concentrations of nitrogen oxides NO x or NH 3 in the fluid upstream of the SCR catalyst, to receive signals representative of the measured concentrations of NO x or NH 3 in the fluid downstream of the SCR catalyst, or any combination thereof; and a signal representative of the NH 3 storage measurement from the at least one RF probe; and an NH 3 storage estimate model configured to determine an NH 3 storage estimate based on at least the signals representative of the measured concentrations of NO x or NH 3 in the fluid upstream of the SCR catalyst or the signals representative of the measured concentrations of NO x or NH 3 in the fluid downstream of the SCR catalyst, or any combination thereof; wherein the controller is configured to utilize at least both the estimated NH 3 storage estimate and the NH 3 storage measurement to output a control action for the injection system. an exhaust aftertreatment system configured to treat emissions from a combustion engine, wherein the exhaust aftertreatment system comprises: a selective catalytic reduction SCR catalyst assembly configured to receive a fluid from the combustion engine, wherein the SCR catalyst assembly has an inlet and an outlet; at least one radio frequency RF probe disposed within the SCR catalyst and configured to measure ammonia NH 3 storage of the SCR catalyst; an injection system configured to inject NH 3 or urea into the fluid upstream of the inlet of the SCR catalyst; a selective catalytic reduction SCR catalyst assembly configured to receive a fluid from the combustion engine, wherein the SCR catalyst assembly has an inlet and an outlet; at least one radio frequency RF probe disposed within the SCR catalyst and configured to measure ammonia NH 3 storage of the SCR catalyst; an injection system configured to inject NH 3 or urea into the fluid upstream of the inlet of the SCR catalyst; a controller communicatively coupled to the exhaust aftertreatment system, wherein the controller is configured to control operations of the exhaust aftertreatment system and to receive signals representative of the measured concentrations of nitrogen oxides NO x or NH 3 in the fluid upstream of the SCR catalyst, to receive signals representative of the measured concentrations of NO x or NH 3 in the fluid downstream of the SCR catalyst, or any combination thereof; and a signal representative of the NH 3 storage measurement from the at least one RF probe; and an NH 3 storage estimate model configured to determine an NH 3 storage estimate based on at least the signals representative of the measured concentrations of NO x or NH 3 in the fluid upstream of the SCR catalyst or the signals representative of the measured concentrations of NO x or NH 3 in the fluid downstream of the SCR catalyst, or any combination thereof; wherein the controller is configured to utilize at least both the estimated NH 3 storage estimate and the NH 3 storage measurement to output a control action for the injection system.