Calibrating Measurements Made During High-Speed Flight: An Application of the New EOL Laser Air Motion Sensor
Presented by: Al Cooper - Earth Observing Laboratory, National Center for Atmospheric Research
Abstract: Measuring properties of the atmosphere from a high-speed aircraft such as the NSF/NCAR Gulfstream GV presents a challenge because the flight speed affects most sensors. Measurements often involve complicated corrections as a result: To measure temperature, corrections must be made for dynamic heating caused by the motion of the aircraftl to measure airspeed, measurements of dynamic pressure, ambient pressure and temperature are needed; corrections are often made to the measured pressure that depend on the airspeed and/or orientation of the aircraft; ect. There are no standards or reliable calibration references for any of these measurements that apply in flight, so uncertainty analyses involve complicated and multi-dimensional examinations of these interactions and of how flight conditions might influence measurements from otherwise carefully calibrated sensors.
A reliable reference for any of these interlinked measurements can be of great value in reducing measurement uncertainty. A new EOL instrument, a Laser Air Motion Sensor (LAMS), now provides such a reference. This instrument measures the Doppler shift in laser light returned from ambient aerosols and provides a measurement of airspeed with less than 0.1 m/s uncertainty. In this talk, I will discuss how various basic measurements of atmospheric state properties are made from a research aircraft, and I will use measurements from the LAMS to demonstrate how the presence of an absolute measurement of airspeed reduces measurement uncertainties not only in the wind but also in pressure and temperature. Uncertainty and precision in pressure, for example, have been reduced to <0.3 and 0.1 hPa, respectiviely, by use of measurements of altitude via GPS, this makes it feasible to map mesoscale pressure fields with high precision. Measurements of temperature have also been calibrated in flight with an uncertainty of less than 0.3 deg C.
An added bonus from the LAMS is that, when combined with calibrated pressure measurements, it can also provide a measurement of the speed of sound and so of temperature. This measurement of temperature does not depend on any other temperature sensor on the aircraft and should remain valid in cloud.
Tuesday January 7, 2014
Refreshments Served at 3;15pm
NCAR Foothills Laboratory
3450 Mitchell Lane
Bldg 2 Auditorium (Rm1022)