A New System for Obtaining Aircraft Derived Atmospheric Observations for Enhanced Weather Forecasting

The accuracy of numerical weather forecasts is highly dependent on the accuracy of its model’s initial conditions. The initial conditions of winds and temperatures above the surface are primarily provided by a set of specially-equipped aircraft which periodically download their observations during flight. These data are incredibly valuable and the most important source for improving wind and temperature forecast accuracy. Unfortunately, even with data from these aircraft, the vast majority of the atmosphere is significantly under-sampled as they make up only a small percentage of the commercial aviation jet fleet which covers only a small fraction of the total airspace. Fortunately, over 90% of commercial aircraft in the US and a growing percentage of business and general aviation aircraft are equipped with Mode Select (Mode S) Enhanced Surveillance (EHS) transponders. Data from these transponders, if properly interrogated, can be derived into accurate wind and temperature observations. It has been demonstrated that such data can be obtained from Mode S EHS equipped aircraft using Secondary Surveillance Radars, but the radars in the US are unlikely to be adapted to regularly perform such interrogations. This paper describes a new low-cost ground-based system that has no moving parts, operates independently from radars, and can equally perform the necessary interrogations. This ground-based system can also provide updates of winds and temperatures, amongst other data, in near real-time and at a rate determined by the needs of the end user. As a result, it can significantly expand the available atmospheric observations for enhanced weather forecasting and other applications.