Radar Pointing
The radar beam may be pointed across the traffic at 90º to the road or in line with traffic
into incoming or outgoing traffic.
Pointing the radar at an angle substantially
different from 90º or 0º is not recommended because the signal strength is severely
reduced.
The industry refers to pointing the radar at 90º as a side firing installation while
pointing the radar in line with traffic is known as a front firing installation. Consult
Operating Mode section
about what types of installations are supported by current
firmware.
Background Clutter
Clutter Map
Since the radar can detect stationary targets, things like fences, road curbs, lane
separators, traffic signs and other unwanted targets need to be processed and eliminated
from the output. In order to do so the radar maintains a clutter map where it stores all
these unwanted targets. The clutter map is subtracted from the signal leaving only true
targets to report.
Clutter Map Time Constant
The radar continuously adjusts the clutter map to account for changing conditions. The
rate of the adjustment is determined by clutter time constant (CTC). CTC specifies how
long does it take for an average target to fade away into the background, e.g. become part
of the clutter map and no longer be reported as a valid target. CTC is a user
programmable value and can be set from 1 second to 28 minutes. For a fast moving
traffic CTC may be set to a lower value whereas for a stopped traffic it is appropriate to
set it to a higher value. Besides automatic continuous adjustment of the clutter map, the
user can issue a command to take and store a quick snapshot of the current clutter map
and use it as a new basis the next time the radar is turned on. Typical use cases are:
1.
You may issue this command during the setup when road is clear of the vehicles
so you do not have to wait for an automatic clutter map adjustment to take place.
This is especially handy in applications where a long CTC is required. A snapshot
command temporarily overrides long CTC value and speeds up clutter map
reconstruction.
2.
You want the radar to start with a “mostly good” clutter map after the power cycle
in order to reduce initial adjustment time.
The clutter map adjustment rate is asymmetric. The clutter is adjusted up slowly (targets
fade away slowly) but is adjusted down fast. This facilitates improved clutter map
maintenance in situations where traffic density is high.
