Experimental Validation of a Forward Looking Interferometer for Detection of Clear Air Turbulence Due to Mountain Waves

Abstract

The Forward-Looking Interferometer (FLI) is an airborne sensor concept for detection and estimation of potential atmospheric hazards to aircraft. To be commercially viable such a sensor should address multiple hazards to justify the costs of development, certification, installation, training, and maintenance. The FLI concept is based on high-resolution infrared Fourier Transform Spectrometry (FTS) technologies that have been developed for satellite remote sensing. These technologies have also been applied to the detection of aerosols and gases for other purposes. The FLI is being evaluated for its potential to address multiple hazards, during all phases of flight, including clear air turbulence (CAT), volcanic ash, wake vortices, low slant range visibility, dry wind shear, and icing. In addition, the FLI is being evaluated for its potential to detect hazardous runway conditions during landing, such as wet or icy asphalt or concrete. The validation of model-based instrument and hazard simulation results is accomplished by comparing predicted performance against empirical data. Models for FLI measurables for mountain wave turbulence were developed during the previous phases of the project. Prior to the field campaign, these models were used to predict what the sensors should have been able to detect, based on expected instrument performance. After the data collection activities, the empirical data was used to update and validate the existing models. This iterative process was employed during the course of the project as new empirical results became available. Previous research programs, focused on forward-looking airborne sensors such as Doppler radars and lidars to detect and forecast turbulence, have produced many tools for analysis, modeling, and simulation. Following on the methods used in the airborne radar turbulence detection problem, relationships between the statistics of an atmospheric disturbance (such as the temperature field) and those of the https://ntrs.nasa.gov/search.jsp?R=20120011814 2018-05-10T00:12:31+00:00ZAmerican Institute of Aeronautics and Astronautics 2 sensor measurements (the spectral radiance) will be developed. In the mountain lee wave data collected in the previous FLI project, the data showed a damped, periodic mountain wave structure. The wave data itself will be of use in forecast and nowcast turbulence products such as the Graphical Turbulence Guidance (GTG) and Graphical Turbulence Guidance Nowcast (GTG-N) products. Determining how turbulence hazard estimates can be derived from FLI measurements will require further investigation.

Aviation Turbulence

“…Detection by passive infrared and microwave radiation techniques, although once promising, simply does not have adequate resolution to truly detect turbulent fluctuations on scales that affect aircraft. However, recently developed technology using interferometry (Schaffner et al 2012) may resurrect this detection technique. In any case, microwave temperature profilers (MTP) are useful for retrieval of vertical temperature profiles taken during field campaigns (Haggerty et al 2014;Mahoney et al 2009).…”

“…Even though passive microwave radiometry had received some attention for airborne CAT detection in the 1960s, its shortcomings for operational use became rapidly evident (e.g., Atlas 1969;Schaffner et al 2012). However, passive sensing techniques such as air temperature microwave radiometry (e.g., Haggerty et al 2014) and star scintillation photometry (e.g., Vernin and Pelon 1986) could be valuable methods for determining ancillary scientific data in general experimental research on atmospheric turbulence.…”

FTIR characterization of atmospheric fluctuations along slant paths

“…A similar ongoing research area to that currently being reported involves the characterization of clear air turbulence using imaging spectroradiometers [3,4]. Here, the temporal variation in water vapor, for example, is used to estimate the amount of atmospheric disturbance for a given look angle.…”

Lidar and Electro-Optics for Atmospheric Hazard Sensing and Mitigation

“…A field experiment was conducted at the University of Colorado Boulder's Mountain Research Station with a current state-of-technology FLI in November 2011. 3 It emphasized measurements for orographic turbulence due to mountain waves. A secondary emphasis was on surface-state measurements relevant to water, snow, and ice on runways.…”