Database Reference
In-Depth Information
Figure 12.2 IMAGE network with STRs.
12.3 Data Set Description
In this section, we detail the different steps required to produce data sets of
aircraft trajectories provided by the IMAGE system. In France, ground radars
send aircraft positions through the RENAR (Reseau de la Navigation Aerienne)
network. Due to network bandwidth limitations we cannot route all raw radar
information toward a single network access point to record it. Therefore, we
use the French IMAGE system. IMAGE is a system that aims to gather aircraft
positions from all French-controlled areas. Its goal is neither to monitor aircraft
activity nor to optimize traffic flow, but to give a general view of the traffic
(communication purposes). The IMAGE system is connected to the five French
STRs (Systeme de Traitement Radar), one in each en-route control center (Fig-
ure
12.2
). STR systems receive aircraft information from different radar sources
and calculate an estimated position for each monitored aircraft (using tracking
and smoothing algorithms). The IMAGE system helps to reduce ground radar
sources to only five data sources, and enables us to retrieve aircraft positions
over France within the RENAR network.
Merging the five data sources raises lots of issues: unique aircraft identifiers,
overlapping areas, time stamps, and sampling rates. First, each STR sends the
aircraft position with an identifier from 1 to 1,023. Since more than 1,023 aircraft
can fly over France at the same time, we extend this identifier to a 16-bit format
and rereassign a unique identifier to every trajectory. To do so, we use a spatio-
temporal frame filtering to assign a new unique identifier to each trajectory: each
radar plot that has the same identifier within a 600 second time frame within
an area of a 200-km (100 Nm, nautical miles) radius (which corresponds to a
12-minute straight flight at high altitude) belongs to the same trajectory. At this
stage, trajectories with less than three plots are removed and no trajectory has
the same identifier.
Secondly, we merge all the five new, reassigned, radar records into one file.
The main issue is to connect trajectories that were recorded by different STR
sources. To do so, we resample all the data to ensure that every record has
