The use of a commercial ADS-B receiver to derive upper air wind and temperature observations from Mode-S EHS information in The Netherlands

Only recently, a new method to derive weather information from aircraft has been developed and tested on quality, availability and applicability for use in operational meteorological applications. This method exploits the information retrieved from an enhanced surveillance (EHS) terminal area radar at an airport. This radar interrogates all aircraft in the range of the radar in a special or selective mode (Mode-S) on which the aircraft responds with information on e.g. heading, airspeed, Mach number and ground track. These messages are transmitted through UHF channels using the Broadcast Dependent Surveillance (BDS) protocol. The so-called Automatic Dependent Surveillance Broadcast (ADSB) data is gathered by ATC and can be combined with tracking information to create Mode-S EHS derived wind and temperature observations in the upper air. The derived observations are of good quality (De Haan, 2011, 2013b) and have proven to be valuable for numerical weather forecasting (De Haan and Stoffelen 2012, De Haan 2013a).

The ADS-B messages can be collected with a wide range of commercial 1090 MHz receivers. This is widely done by aircraft spotters all over the world. The data protocols are described in ICAO and EUROCAE/RTCA documentation and this opens the opportunity to install an ADS-B receiver to downlink the Mode-S EHS data as interrogated by ATC The Netherlands.

In this report we describe the installation of a commercial Mode-S/ADS-B receiver, the software to extract meteorological information from Mode-S EHS/ADS-B EHS data and a first quality assessment by comparing the ADS-B EHS with the Mode-S EHS observations provided by ATC The Netherlands. Horizontal coverage density plots will reveal some shortcomings of the new method, that is, only a small fraction of the Mode-S EHS messages are also retrieved by our ADSB receiver. However, the messages that are received are of fairly equal quality and have a more southward coverage due to the different location of the antenna.

The limited capability of the ADS-B receiver to derive wind and temperature observations is mainly due to a lack of simultaneously available parameters which is necessary to derive meteorological information from the transmitted messages. During rush hours the percentage of received valuable ADS-B EHS information drops to 8% compared to the Mode-S EHS data provided by ATC.

In this report it is shown that

1. ADS-B EHS data can be received independently from ATC, on the condition that aircraft are interrogated by a Mode-S EHS radar. A commercial ADS-B receiver is capable of receiving the Mode-S EHS information.

2. The received ADS-B EHS parameters contain information which can be used to derive wind and temperature observations.

3. The volume of the received meteorological data is a fraction, around 8 %, from the Mode-S EHS data flow in use by ATC The Netherlands.

4. The quality of the derived meteorological information is slightly worse than the meteorological data derived from the Mode-S EHS data received from ATC. Wind speed and direction are within meteorological requirements. Air temperature derived from ADS-B EHS is not compliant to these requirements.

As at present the rapid update cycle of the numerical weather prediction model of KNMI uses about 2 % of the Mode-S EHS data it is expected that the same relevant meteorological information can be received through a local ADS-B receiver. For reasons of coverage, amount and quality of the data, as well as cost efficiency, the reception of Mode-S EHS data from ATC is preferred.