HCR Test Flights

The NCAR HIAPER Cloud Radar (HCR) has concluded its 12-hour test flight program on 1 December 2014, after a nearly four-week long test campaign. The test flight program provided HCR an opportunity to verify the functionality of the newly implemented capabilities: an Active Pressurization System (APS) and automatic shutoff control, and a real-time B-scan display. The program also allows HCR to further verify its standard calibration procedure, pointing accuracy, and address the deficiencies identified during the IDEAS-IV campaign.

The HCR on the wing of the NSF/NCAR HIAPER during a test flight over eastern Colorado. Photo by Chirs Burghart NCAR/EOL.
The HCR on the wing of the NSF/NCAR HIAPER during a test flight over eastern Colorado. Photo by Chris Burghart NCAR/EOL.

The Active Pressurization System (APS) provides supplemental pressure (nitrogen) to the main radar electronics vessel to maintain its essential operating condition. The APS was designed according to the leak rate identified during IDEAS-IV and should maintain operational conditions for up to 10 hours. The APS was tested in four different flight profiles to investigate its capability and the overall leak rate of the system. At lower altitudes (16,000 to 25,000 ft), an average 0.3% nitrogen volume loss was observed. Also an average of 0.5% volume loss was observed at the 40,000 ft flight level, in contrast with the 4.2% leak rate during IDEAS-IV.  The engineering efforts that went into improving the seal condition of the main radar electronics vessel were extremely successful. The new minimal leak rate means HCR can operate for longer duration in flight. 

This is a dataset taken during the last test flight on December 1. As the aircraft fly west toward the foothills, HCR flew over the devils thumb peak. The clouds were low and around -35 dBZ.

Because of HCR’s unique near-nadir pointing capability, the radar system is more susceptible to strong return echo. In order to protect the radar from damaging return power, the Automatic Shutoff Control was introduced. It automatically switches in and out of the protection (attenuated) mode depending on the pointing angle, the altitude above ground level, the presence of water or ground, and the return power. The Automatic Shutoff Control responded correctly to the altitude thresholds, the water indices of digital terrain map, as well as the real-time detected maximum power. This successful result ensures a well-protected radar system and also provides great confidence in the future remote operation capability.

HCR is now equipped with a real-time, flight-altitude-capable Bscan display (HawkEye). It displays the radar data relative to flight level according to its pointing angle – nadir or zenith.  A more intuitive plot of the clouds above and below the aircraft is presented to the operator. Different variables such as reflectivity, velocity, LDR and raw fields are available.  This versatile display will be integrated into the HSRL system to eventually display HCR and HSRL product simultaneously. 

A total of four standard pointing calibration maneuvers were performed. The HCR team was able to calculate the pointing bias from the first flight and applied the correction for the remainder of the program. From the preliminary analysis, the calibration maneuvers provided good data in order to calculate the pointing bias and the correction result gives a good ground velocity estimate, i.e. 0 m/s. Reflectivity as low as -42 dBZ at 1 km, was observed on November 20, 2014. This sensitivity is in close agreement with the theoretical calculation -43.6 dBZ.

Peisang Tsai, HCR engineer, pleased with the HCR test flight results. Photo by Chris Burghart NCAR/EOL.

Doppler artifacts in turbulence condition were identified during IDEAS-IV. The radial velocity deviates both positive and negative and the spectral width only deviates in positive direction. HCR has adapted a high-rate (100Hz) inertial data stream to mitigate this deficiency. Valuable datasets in turbulence with cloud echoes present were collected to evaluate the performance.

With the improved ability to operate for longer duration, protect the radar system from strong returns and enhanced in-flight display, HCR is closer to being ready for its first deployment, CSET, in June 2015.