That is a bird tracking radar antenna to detect and track birds in the vicinity of the airport. The vertical component is used to determine the bird's altitude.
ROBIN's 3D Flex system consists of a horizontal S-band radar, combined with a flexible Frequency Modulated Continuous Wave (FMCW) radar. The horizontal S-band radar identifies the presence and number of birds in time – including their location, height, direction, speed and route – up to 10 kilometres away, all around, day and night.
The FMCW radar has three modes:
- 'Scanning' mode, by which 3D information is retrieved for all desired directions.
- 'Staring' mode, in which the radar points in one direction to identify targets up to 6 km away.
- 'Automatic Acquisition' mode, where the vertical X-Band radar slews in azimuth to the cue of the horizontal S-Band radar, based on the objects with highest RCS. In this way much of the bird tracks (in all directions) will be assigned elevation data.
(Robin Radar Systems - 3D Flex Radar System - Bird Strike Prevention in 3D)
Apparently, Amsterdam Schiphol was the first airport to be equipped with such a radar system in 2013 due to a large number of geese in the vicinity:
Schiphol first deployed a single bird radar (Robin 3D Flex) at
the ‘Polderbaan’, one of it’s six runways. After successful
testing Schiphol acquired four more 3D Flex radars to cover the
Robin Radar Systems’ 3D Flex radars detect and track birds in
and a round the airport up to 6-8km away. They also provide the
height information of the birds. Each bird controller receives
the radar data on an iPad in their vehicles.
(Robin Radar Systems - Schiphol Case Study)