The data received by EMADDC from ANSPs primarily adheres to the ASTERIX format, with CAT48 and CAT62 providing the relevant surveillance information utilized by EMADDC for generating observations. Historically, MUAC has transmitted sizable data batches to EMADDC at 15-minute intervals using the CAT48 format. In contrast, the new real-time data received through NewPENS is in CAT62 format. EMADDC has limited prior experience with this format, aside from decoded data from AustroControl (AU). Consequently, time has been allocated to assess the quality and volume of observations derived from this data. To aid understanding, a brief overview of the key differences between these formats is provided in this news article. 

The ASTERIX CAT48 format contains individual messages containing all responses received from aircraft transponders for each radar station. This is comparable to the content of Mode S / ADS-B messages captured by a receiver, though formatted differently. Additionally, in CAT48 data the aircraft position is obtained through radar measurement, whereas receiver data includes the position information directly transmitted from the aircraft within an ADS-B position message. Furthermore, CAT48 messages include proper decoding and quality checks as radars know the content of received responses (which are unknown to Mode S / ADS-B receivers and hence require smart logic to properly decode the messages).  

The ASTERIX CAT62 format originates from an ATC tracking system — a sophisticated processing platform that receives CAT48 messages from radars within its operational area. It consolidates these messages into a unified output stream of “radar blips” at a consistent interval (typically approximately every 4.2 seconds). The system also employs regression techniques to enhance the accuracy of aircraft position. If, for a given aircraft, no new relevant data (such as true airspeed, roll angle and other parameters) is received, the system retains the most recent data until it becomes outdated. Once the data is considered too old, output for that aircraft is temporarily halted until new responses are received. Fortunately, the format includes the "age" of each parameter, which EMADDC can use to improve the accuracy of the observation timestamp and apply this information for filtering purposes. 

These processing steps present several challenges and limitations in the handling of data by EMADDC. Primarily, the tracker retaining "old" data under a new timestamp leads to the formation of "pseudo" or duplicate observations that do not contribute any new information and can result in data redundancy. This issue is illustrated in the diagram below.

This illustration displays the age and value of the roll angle. As the age increases, the value remains constant and does not provide additional information. When a new transponder response is received, the age is reset to a lower value, and a new value may be obtained; however, this is not always the case, as certain parameters—such as FL—may remain unchanged. Consequently, EMADDC filters out all messages with an age exceeding that of the tracker interval rate (4.8s). Additionally, EMADDC verifies that the ages of all parameters are sufficiently synchronized in time; if there is a significant time gap, those observations are also excluded.  

Finally, if multiple new messages for an aircraft are received from different radars within the 4.8-second interval of the tracker, only the most recently received message is output. This represents another form of filtering applied to CAT62 data, although it is not performed by EMADDC. 

Another potential issue in CAT62 data is the reduced resolution of the Mach number which MUAC countered by providing the Mach at higher resolution in CAT062 I062/380 subfield #4 as outlined here.

All of the steps outlined above lead to a significant reduction—in the range of approximately 50-60%—in the number of observations generated from the MUAC CAT62 data stream by EMADDC, while maintaining the same observational quality. Given the substantial volume of observations produced by EMADDC, this reduction is considered manageable. Additionally, the data is now available in real time and can be processed instantly within the upcoming EMADDC 3.0 system.  

The EMADDC acceptance system has initiated processing of the MUAC CAT62 data (referred to as muac-cat62) and has completed the transition from the previous muac data. The production system is scheduled to implement the same update by the end of June. 

Currently, EMADDC is in discussions with additional stakeholders to enable real-time data transmission through NewPENS. These new suppliers have indicated their ability to provide data in the preferred CAT48 format; consequently, a reduction in data volume is not expected there.