Airborne Coherent Lidar for Advanced In-Flight Measurements (ACLAIM) — Flight Testing of the Lidar Sensor

The detection of turbulence before it reaches the airplane has been a goal of the ACLAIM program since its inception in 1994. ACLAIM stands for Airborne Coherent Lidar for Advanced In-flight Measurements, and was a NASA/Dryden-led program to develop and demonstrate an airborne Doppler lidar system for look-ahead turbulence detection. Turbulence detection has several tangible benefits for commercial airplanes. Clearly, if turbulence can be detected before it affects the airplane, warning issued to the passengers and flight attendants can reduce injuries significantly. Operating in conjunction with to-be-developed flight control algorithms, the warning of turbulence can be used to change the autopilot mode, potentially reducing the peak vertical accelerations, or even used as input to the flight controls system to directly counteract the effects of turbulence. Of the available turbulence sensors, particularly for Clear Air Turbulence, the lidar is the most appropriate, and certainly the most developed.

The ACLAIM program has developed a lidar system which is intended to be used in prototypes of the systems described above. In late March and early April of 1998 we performed the first flight tests of this lidar system. These flight tests are the first in a series of tests of the lidar sensor. While future tests will include a system to scan the laser beam, for this test the laser beam was aligned with the airplane flight path. The aircraft was NCAR's Lockheed Electra operated from their facility in Broomfield Colorado. This aircraft has a sophisticated array of aerosol instrumentation, a gust probe, global positioning equipment, and data acquisition systems to allow comparisons between the lidar and the aircraft systems. We obtained about 14 hours of flight data over 5 flights. . In this report we will present a subset of the data concentrating on the velocity and turbulence measurements.