Calibration, Sensitivity, and Doppler Spectra of the NCAR Airborne W-Band Radar

The HIAPER Cloud Radar (HCR) is a 94 GHz scanning W-band system which is mounted in an underwing pod on the NSF/NCAR HIAPER aircraft. Because of the radar's exposure to extreme environmental changes, radar system calibration presents unique challenges which makes monitoring of system stability especially important. HCR has been deployed in several field campaigns, most recently during the Southern Ocean Clouds, Radiation, Aerosol Transport Experimental Study (SOCRATES) which took place in early 2018.

We use data from SOCRATES to demonstrate some of the applied calibration and quality control procedures, solutions to particular problems that occurred during the field campaign, as well as additional efforts to increase data quality. Topics we will present include:

• The correction of the temperature sensitivity of the receiver using data from several temperature sensors within the radar in the context of the noise source calibration.
• The use of the backscattering properties of the ocean surface as a calibration reference, which shows consistent radar performance throughout the field campaign.
• The comparison of the ocean surface backscattering calibration with other calibration methods that make use of known maximum thresholds of reflectivities, to provide an independent assessment of the radar calibration.
• Preliminary results from recent radome loss measurements with and without water films.
• The minimum sensitivity of HCR for detecting cloud boundaries.
• Compensation for Doppler spectrum spread due to aircraft motion.
• Possible estimation of vertical air motion in precipitation using the Mie-notch in Doppler spectra due to the presence of droplets that are 1.7 mm in size.

We will further provide a summary of how these different procedures are combined to produce high-quality data which are provided to the scientific community.