After successful ground-based tests, the Icing branch of the NASA Glenn Research Center began collaborating with ProSensing Inc. to develop an airborne, multi-frequency radar to test the technique in realistic in-flight icing conditions.
The radar system, now under development, was designed with two millimeter wavelength channels (1.0 and 0.3 cm) to extend the liquid water range of the sensor and to maintain accuracy in non-Rayleigh precipitation. The radar system consists of pulsed X (9.4 GHz) and Ka-band (35.5 GHz) radars, both employing 25 kW magnteron transmitters, and a dual-antenna FMCW W-band (95.0 GHz) radar. With the RF sections housed in a single forward looking pod, the three radars will sample similar sample volumes with 12”, 5.5” and 3” diameter antennas at 9.4, 35.5 and 95.0 GHz respectively. Engineering test flights of the multi-frequency radar system are planned for the NASA Twin Otter research aircraft in early 2004.
This paper will introduce the measurement technique, show examples of multi-frequency radar retrieved liquid water and drop size parameters from past ground-based experiments, and describe the airborne radar system.
 Vivekanandan, J., G. Zhang, M. K. Politovich, 2001: An Assessment of Droplet Size and Liquid Water Content Derived from Dual-Wavelength Radar Measurements to the Application of Aircraft Icing Detection. Journal of Atmospheric and Oceanic Technology: Vol. 18, No. 11, pp. 1787–1798.
 Pazmany, A. L. 2001 :Millimeter-Wave Radar Field Measurements and inversion of cloud parameters for the 1999 Mt. Washington icing sensors project, NASA Tech. Briefs CR-2001-211103, August.
 Pazmany, A. L. and J. B. Mead, 2000: Estimation of LWC and Drop Size from Multi-Frequency Radar Reflectivity Profiles with an Artificial Neural Network, 2000 In-Flight Icing Remote Sensing Workshop, Nov. 16-17.