Police and Security Applications:
Government Flying Services
Hong Kong

The aim of the GFS is to achieve worldwide recognition as a provider of excellent search, rescue and aviation support services.

Based at the New Hong Kong International Airport (Lantau), having moved there from Kai Tak in June 1998, the GFS operate two fixed wing Jetsteam J-41 maritime reconnaissance aircraft in addition to three Eurocopter Super Puma L2 and five EC155 helicopters. All GFS aircraft are modified to carry gyro-stabilised Forward looking infra-red (FLIR) and colour video camera role equipment.

Command and Control
In 2001, as part of their ongoing development programme, Government Flying Services invited a number of companies to submit quotations to significantly upgrade their existing Microwave downlink system so as to provide officers in the GFS operations control room at Lantau with real time FLIR and colour video images from up to four aircraft, simultaneously. The objective being to improve the level of information and control available to operators in the GFS control room by providing them with the same audio and visual information that is available to the crew of each aircraft.

Apart from supplying new ground receive antenna systems, the RTQ included provision for a VHF datalink to be installed on two Jetstream J41 fixed wing plus Eurocopter rotary wing aircraft. This datalink being used to provide information about the position, direction, speed, and altitude of the aircraft to the four ground receive sites as well as provide current aircraft flight information, through a Digital Mapping System, to GFS operations room personnel.

In late 2001, after carefully evaluating all the tenders, Government Flying Services awarded Gigawave the contract. Apart from purely financial considerations, GFS were impressed by the level of experience and expertise shown by Gigawave engineers both in terms of GPS based antenna systems and their ability to customise the system to meet specific GFS requirements.

System Overview
The initial contract called for a self-contained GPS datalink module, incorporating a GPS receiver and VHF transmitter, to be installed in both Jetstream aircraft and Eurocopter helicopters. The datalink module in each aircraft utilises existing GPS and VHF antennas and is pre-programmed with a two letter aircraft 'ID'. This is used to identify the aircraft by both the ground receive antenna pantable controller and the contol room 'mapping' computer.

The self-contained datalink module consists of a GPS receiver which feeds data through a modulator into a VHF transmitter. Serial packets of GPS data are transmitted on the same frequency from each aircraft to receivers co-located at each of four ground receive sites. Each aircraft sends its data at specific time intervals, determined by the GPS time reference signal.

The original ground receive site at 'Tai Mo Shan' (TMS) has been augmented by three new sites including one on Victoria Peak (VP). These strategically located sites provide line-of-sight coverage over the whole of the Hong Kong Special Administrative Region 'and the South China Sea.

Ground Receive Sites
Each ground receive site consists of a Gigawave GPS Auto-Tracking Antenna System which uses GPS data via a RS485 link from the co-located VHF datalink receiver to calculate the bearing to a particular aircraft. Using a touch screen controller in the operations control room at Lantau, an operator can instruct each of the ground receive sites to track any one of up to ten aircraft. Alternatively all four ground receive sites can be used to track the same aircraft, depending on operational requirements.

Up to 12 microwave downlink frequencies in the C-Band can be pre-programmed into the aircraft transmitter and manually selected by the crew. The frequency of the downlink receiver is automatically assigned by the 'control' computer in GFS HQ at Lantau, according to which aircraft the ground receive site is tracking. All data communications between the GFS operations room and each ground receive site uses a bi-directional RS232 cable link via the Police HQ in Hong Kong. Images are relayed from the ground receive site to the operations room and other locations using terrestrial microwave links and optical fibre.

Environmental Considerations
Due to their exposed location, each ground receive antenna is subject to harsh environmental conditions, especially during the typhoon season. For this reason only the 25dBi offset-fed antenna and 360 degree pan-table are installed in the mast-mounted radome, with the MVL series receiver, pan-table controller, local slave controller, and peripheral equipment are housed in an adjacent equipment room. As all four ground receive sites are shared with radar and other communications facilities a Band Pass Filter is used to filter out unwanted RF signals before being fed into a circulator (with 50 Ohm load) and LNA (low noise amplifier)

For test purposes, the ground receive site at 'Tai Mo Shan' (TMS) has a GPS data link and C-Band microwave transmitter, identical to those which are installed in each aircraft, located a few metres away from the receive site. At any time the operator in in Air Command and Control Centre (ACCC) at GFS HQ can select 'Test' mode on his touch screen display and can check the operation and performance of each receive site as they 'track' the test site. Should the RS232 link fail for any reason whilst in 'Test' mode, the test transmitter will default to 'normal' mode after 15 seconds.

Government Flying Services provide a wide range of airborne services to the Government of Hong Kong 'Special Administrative Region', including searching for illegal immigrants, maritime patrols, aerial surveys, and VIP transportation. However, one of the major responsibilities of the GFS is to provide airborne emergency services, and especially SAR operations within a 400-mile radius of the Hong Kong Flight Information Region (FIR). A typical SAR mission would entail using the Jetsteam J-41 maritime reconnaissance aircraft to locate and monitor the incident and then to use one or more of the rotary wing aircraft to initiate the rescue.

With the new system, it is possible for personnel manning GFS operations in ACCC to see real time images from the gyro-stabilised FLIR or colour video camera and see the location, direction, and track of each aircraft superimposed on a map of the Hong Kong 'Special Administrative Region', on separate plasma displays.

Each GFS aircraft on the map display is represented by a helicopter or aeroplane 'icon', which changes direction according to the track of the real aircraft. In addition to the two large plasma displays, the controller has a touch screen display which allows him to select which ground receive site is to track which aircraft and which images are to be displayed full size on the plasma screen. The touch screen display also provides the operator with system status information as well as manual override and test facilities.

One of the two large plasma displays in the operations room at GFS HQ is split into five panels with four small panels displaying real-time images from each ground receive site and one larger panel on which a full size version of any one of the four smaller images can be displayed. The second plasma display is used to display a map of the 'Special Administrative Region' extending for 50 nautical miles south of Hong Kong Island.

In addition to individual aircraft 'icons' the operator can:

The whole system is controlled by a computer located in the operations control room, with a second computer providing the 'mapping engine' that drives the map display. Both computers are backed up by a third computer that is loaded with both the system control and mapping software.

Installation of the new system was completed in May 2002 by Gigawave engineers working alongside GFS personnel and external contractors. Since being commissioned, the system has been in constant use and has exceeded all GFS expectations. So much so that Gigawave software engineers have been asked to extend the range of the map from 50 nautical miles to 200 nautical miles and to provide GPS datalinks for all ten of their aircraft. This upgrade will allow controllers to visually monitor the exact location of their two Jetsteam fixed wing aircraft as well as their three Super Puma L2 and five EC155 helicopters at the same time.

For more information about Government Flying services, visit their website at:
www.info.gov.hk/gfs/home.htm