ASTERIX Category 048: what one radar detected

A Category 048 record is one plot or one local track from one radar. Position arrives as slant range and azimuth measured from a station whose own location the format never carries.

The category also allows the report to describe something that is not an aircraft at all. It has codes for a reflection, a sidelobe reply, an angel, a phantom plot, a bird and a wind turbine, and a reader that assumes every report is a target will produce a picture full of things that are not there.

As with the other categories, there is no checksum. Structural conformance is the integrity gate, and the checks that passed are recorded on every object produced.

Monoradar reports are the closest thing to raw measurement that a surveillance network exposes. Working from them means the decision layer can see the measurement rather than a downstream tracker's interpretation of it.

The non-target codes are operationally significant. Distinguishing a wind turbine return from a slow moving contact is exactly the kind of judgement that ought to be visible in a decision record rather than buried in a filter.

For counter-uncrewed-aircraft work, the low, slow and small problem lives in this category's quality fields, not in a downstream summary.

Ingest produces one Entity and one Event per record, in block order.

Two values are injected by the caller rather than taken from the payload: the clock, which supplies the date the time item lacks, and the sensor position, which supplies the site the format never carries. Both are supplied once at construction and both are visible in every golden fixture.

Without a site position the default behaviour is the conservative one. The polar measurement is parked and no geographic position is produced at all. With a site and a height item the geometry is derived, the arithmetic used is declared on the object, and the raw range and azimuth integers are still parked, because a derived position is a one-way view and egress re-emits from the integers.

The adapter never obtains a site for itself. Reading one out of another payload, or resolving a source address through a lookup table it carried, would be a station configuration discovered from the data, which is a different act from accepting an argument.

One geodesy question in the pinned specification could not be answered from that document. It is recorded as an open gap in the coverage file rather than closed by a plausible assumption.

Egress re-emits Entities that came from Category 048 as one byte exact data block. Anything else is refused with a message naming what is missing.