NASA Icing Remote Sensing System (NIRSS) 

The NASA Icing Remote Sensing System (NIRSS) deploys a vertically–pointing K–band radar, a lidar ceiliometer, and a profiling microwave radiometer to obtain measurements for diagnosing local inflight icing conditions. RAL is working with NASA GRC to develop algorithms and data ingest and display software for the system.

NASA has an ongoing activity to develop remote sensing technologies for the detection and measurement of icing conditions aloft. As part of that effort NASA teamed with NCAR to develop software that fuses data from multiple instruments into a single detected icing condition product. The multiple instrument approach, which is the current emphasis of this activity, utilizes a K–band vertical staring radar, a microwave radiometer that detects twelve frequencies between 22 and 59 GHz, and a lidar ceilometer. The radar data determine cloud boundaries, the radiometer determines the sub–freezing temperature heights and total liquid water content, and the ceilometer refines the lower cloud boundary. Data is post–processed in C++ program with a Java–based web display of resultant supercooled LWC profile and aircraft hazard identification. In 2010, a multi–channel scanning radiometer, designed and built by Radiometrics, Inc. under a SBIR grant, ,was added to the system to assess its utility in improving icing diagnoses.

Instrumentation

Each instrument is connected to a laptop computer to log data and monitor instrument status every minute. The individual laptops are connected to a central server that ingests data, performs calculations, and displays time–height instrument data and icing hazard.

• Radar: METEK Ka-band radar
• Microwave radiometer:
  Radiometrics, Inc. TP/WVP 3000 Temperature and Water Vapor (3-6 degree beamwidth)
  Radiometrics, Inc. scanning Ka and W-band radiometer (1 degree beamwidth)
• Ceilometer: Vaisala CT25K Laser Ceilometer

NIRSS

The NIRSS algorithm ingests the raw instrument input files, inputs appropriate fields into a database and performs basic quality control and time matching. Using fuzzy logic, the radiometer ILW is distributed within the detected cloud layers. In the flow diagram below, red lines and boxes are new inputs and modules for NIRSS should NIRSS eventually be combined with polarized NEXRAD moments.

• Prototype module for temperature profile adjustment with thermal IR sensor for inversion detection
• Prototype module for utilizing Ka-band fall velocity spectra for mixed-phase conditions detection
• Development of new 1 degree beamwidth scanning radiometer
• Compare NIRSS results with newly available polarized S-band radar moments
• Compare NIRSS results with new prototype supercooled liquid water sonde profiles

As NIRSS moves toward a stand–alone icing detection system that could be transferred to commercial vendors for airport area deployment, we see the following possibilities for improvement:

• Improved cloud and liquid distribution
• Adjustment of temperature profile
• Freezing rain and drizzle flags
• Refining drop size detection capability
• Merging S-band polarized radar moments into NIRSS algorithm