NPOESS Aircraft Sounder Testbed-Microwave (NAST-M): instrument description and initial flight results

The National Polar-Orbiting Operational Environmental Satellite System (NPOESS) aircraft sounder testbed (NAST) has recently been developed and deployed on the NASA ER-2 high-altitude aircraft. The testbed consists of two co-located cross-track scanning instruments: a Fourier transform interferometer spectrometer (NAST-I) [1] with spectral coverage of 3.7–15.5 m and a passive microwave spectrometer (NAST-M) with 17 channels near the oxygen absorption lines at 50–57 GHz and 118.75 GHz. The testbed provides the first coregistered imagery from high-resolution microwave and infrared sounders and will provide new data that will help 1) validate meteorological satellite environmental data record (EDR) feasibility, 2) define future satellite instrument specifications, and 3) demonstrate operational issues in ground validation, data calibration, and retrievals of meteorological parameters. To help validate the performance and potential of NAST-M, imagery was collected from more than 20 overpasses of hurricanes Bonnie and Earl during the Convection and Moisture Experiment (CAMEX-3), Florida, Summer 1998. The warm core and convection morphology of Hurricane Bonnie (August, 1998) is clearly revealed both by aircraft-based microwave brightness temperature imagery and temperature retrievals within the eye. Radiance comparisons with the Advanced Microwave Sounding Unit (AMSU) on the NOAA-15 satellite and radiosonde observations yield root mean-squared (RMS) agreements of approximately 1 K or less.