Title of Presentation: Passive A-Band Wind Sounder (PAWS) for Measuring Wind Velocity

Primary (Corresponding) Author: Shane Roark

Organization of Primary Author: Ball Aerospace

Co-Authors: Robert Pierce, Christian Grund, Philip Slaymaker, Pei Huang, Paul Kaptchen

Abstract:  The objective for the Passive A-Band Wind Sounder (PAWS) is to demonstrate an instrument concept for measuring tropospheric wind speed profiles from Doppler shifts in oxygen absorption features. PAWS is a daytime-only approach and is not expected to provide the level of accuracy, precision, or spatial resolution that is anticipated for Doppler lidar. However, PAWS has the potential to provide much better wind data than is available in the near term with significantly lower cost, risk, and platform requirements than lidar.

PAWS is in the third and final year of funding through NASAís Instrument Incubator Program. During the first two years of this project, a breadboard instrument was designed, constructed, and tested, and development of instrument and atmospheric models was initiated. The breadboard was used as a path-finding tool and sacrificed stability in order to accommodate a number of possible orientations and measurement schemes. This approach enabled a thorough, yet economical assessment of the effect of each instrument component on the measurement. Test results demonstrated that all of the instrument components performed collectively to enable phase measurements with very high resolution; however, instrument drift from thermal and mechanical instability precluded measurement of actual wind-induced Doppler shifts.

Results from breadboard testing, experimentation, and analysis were used to refine the engineering unit instrument design. The engineering unit consists of pre-filters, an air-spaced etalon, a monolithic Michelson interferometer, and CCD detector all bonded into a block of low-CTE ceramic. This arrangement produces a very stiff and thermally insulating structure. Analysis indicates that the stability during a measurement can be maintained below an equivalent Doppler shift of 1 m/s with modest temperature and pressure control on the etalon an interferometer.