Contrail Prediction Program

    Contrails, or condensation trails, are the cloud-like streamers that sometimes appear behind aircraft as they cross the sky. When contrails are produced by an aircraft, obvious implications arise for the detection of military aircraft. In response to Air Weather Service requirements, the Air Force Research Laboratory's Tactical Environmental Support Branch of the Space Vehicles Directorate at Hanscom Air Force Base, Massachusetts, initiated a research program to improve contrail forecasts.

    Contrails are produced by an aircraft when a particular set of conditions exist relating the state of the atmosphere (air temperature, relative humidity and pressure) and the aircraft exhaust (the ratio of moisture-to-heat production). If the mixture of ambient air and aircraft exhaust is saturated or supersaturated, a contrail will form. Therefore, calculations which determine the likelihood of contrail formation must include the aircraft engine characteristics as well as accurate atmospheric conditions.

    The Tactical Environmental Support Branch program is aimed at improving the contrail forecasts over specific areas and at specific altitudes. The branch conducted a 10-day Contrail Field Program in September 1995. Radiosonde launches and aircraft observations, during daylight hours, were made at five sites in eastern Massachusetts, including Hanscom Air Force Base. The aircraft sitings (including whether or not the aircraft produced a contrail) were coordinated with an observer at the Federal Aviation Administration Control Center in Nashua, New Hampshire, who documented the aircraft type, aircraft altitude, aircraft speed and aircraft heading. A total of 562 aircraft observations were documented.

    The Tactical Environmental Support Branch has developed a contrail prediction algorithm that determines the likelihood that an aircraft flying in certain environmental conditions will produce a contrail. The contrail-YES/contrail-NO observations collected during the Contrail Field Program were used to test the accuracy of the new contrail predication algorithm and the algorithm that is used operationally at the Air Force Global Weather Center.

    Results indicate that the new contrail prediction algorithm developed by the Tactical Environmental Support Branch provide a dramatic improvement in the ability to forecast contrails. The new algorithm produced accurate contrail forecasts 85 percent of the time compared to 57 percent correct for the Air Force Global Weather Center operational contrail prediction algorithm. The new contrail prediction algorithm also showed significant improvement in the Probability of Detection and False Alarm Rate statistics.

    The Tactical Environmental Support Branch has begun work to develop other new contrail prediction algorithms for global use, especially in data-denied areas where radiosonde observations are not routinely available. Work has recently begun to develop contrail prediction algorithms based on numerical weather prediction model output and satellite sounding and imagery (various channels) data. The goal of all these efforts is to improve guidance for mission planners regarding the probability of contrail occurrence during planned operations. The Tactical Environmental Support Branch's development of contrail forecast algorithms will contribute to this goal, thereby providing better protection for our warfighter.

-AFRL-

(Current as of January 1998)


For more information, contact:
Public Affairs
Air Force Research Laboratory
Space Vehicles Directorate
Voice: (505) 853-3515 or DSN: 263-3515
Fax: (505) 846-2178 or DSN 246-2178
3550 Aberdeen Ave SE
Building 497
Kirtland AFB, NM 87117-5776