ASI eSODAR

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Aviation Systems International (ASI) has pioneered the next generation of high performance enhanced SODAR wind profilers and wake turbulence measurement systems, eSODAR. Designed for all weather operations in high noise environments such as airports and the urban environment.

The implementation of a proprietary calibration mode, optimizing the system using the real time atmospheric and environmental conditions, makes this the most advanced SODAR measurement system in the World. Results are provided real-time, not averaged over 10 minutes like other SODAR units.

ASI developed the eSODAR systems specifically for the airport environment. The issues noted by NASA (1) and ongoing implementation programs in Europe and the US were used to develop the ASI eSODAR systems. Altitude availability is highly dependant on ambient noise and atmospheric conditions. The eSODAR was designed specifically with sound shielding tuned to the system, aircraft, and vehicle noise. The enclosures minimize the noise from the system, and therefore can be installed without issue in airport and urban environments (even installed on top of buildings).

The bistatic system uses large diameter dishes (1.2m) along with a specific offset to minimize the scattering effects of higher wind velocities, while still able to capture thermal turbulence of low wind speeds at altitude. A bistatic design allows for a high update rate of the resultant measurement.

ASI enclosure

Rain fade and fog attenuation are not only physically minimized by the enclosure design, a proprietary system balancing mode monitors and adjusts system parameters real-time.   The system is constantly monitoring the attenuation and signal strength at altitude. The system will adjust accordingly to optimize measurement according to the real-time MET conditions, and not just by increasing the signal power. This capability allows the system to provide measurements in light to medium rainfall, and the top of fog/relative intensity, even with multiple inversion layers. Special hydrophobic coatings are used to minimise attenuation due to rain, fog, and dust storms.

The system provides feedback to the operator, showing if there is anticipated loss below certain altitude, a timeframe for loss of measurement capability, and an estimate of return to measurement.

Ambient noise is not masked within the software, it has been mitigated by the design of the system and its enclosure. The enclosure prevents direct signal coupling between the transmitter and receiver, allowing for much lower altitudes of measurement levels to to 10m above the system. A review of field measurements (not the advertised specification) from other SODAR systems show that the direct signal prevents measurements below 50m to some around 100m. This is far from adequate to determine near surface turbulence important for measurement of wake turbulence advection and demise, EDR/TKE, and fog mitigation.

There is much information from SODAR manufacturers on real-time measurement capability. While a system may be broadcasting a signal real-time, due to the ringing in the system (phased) and other factors, the resultants are averages of 10 minutes of measurements and more. This averaging is not sufficient to accurately describe EDR and TKE, and cannot be used for Low Level Wind Shear Alert Systems (LLWAS), wake advection and demise calculations.

The ASI eSODAR provides a resultant measurement of wind speed, wind direction, and vertical windspeed every 15 seconds to 300m, meeting the standards for LLWAS. At this update rate, reporting the horizontal and vertical winds, the systems provide the data for EDR and TKE determinations. This enables many current and future air traffic management operations such as Time Based Operations, RECAT, and wake turbulence mitigation/advisory systems.

The ground based winds aloft from the Wind Profiler can be used by Air Traffic Control and Air Traffic Management Systems to augment the AWOS surface winds providing optimization of the runway capacity and enhanced situational awareness to aircrews. As an example, the wind aloft data can be used for runway end selection, noting the headwind/tailwind component by altitude, and showing if aircraft specifications are exceeded.

Winds aloft for final approach, LLWAS, wake turbulence mitigation strategies, and fog nowcast systems are now a viable reality in the airport environment.

For the aircraft, the winds aloft can be sent directly to the flightdeck using several methods, providing increased situational awareness to the flight crew on the actual wind conditions on final approach. The wind profile data can be ingested directly into the Flight Management System, providing enhanced wind information for the automation, such as the onboard automated windshear alert system. The aircraft automation response becomes proactive, instead of reactive.

ASI eSODAR wind profiler, wake turbulence measurement, and fog nowcast systems have been designed and tested for aviation use in the airport and urban environment.

References:

  1. Atmospheric Boundary Layer Sensors for Application in a Wake Vortex Advisory System NASA technical report