DPWX/Initial Multiple Angle Snow Camera-Radar experiment (MASCRAD) project operations: 15 November 2014
Authors: Patrick C. Kennedy and Branislav Notaros
Personnel from the CSU Electrical and Computer Engineering Department and the dual-fence wind screen that they have constructed to protect the precipitation sensing equipment used in the Multi-Angle Snow Camera and Radar (MASCRAD) project. Additional project information and selected initial data examples have been assembled.
Picture credit: B. Notaros
Data collection for the Multi-Angle Snow Camera and Radar experiment (MASCRAD) project started in November, 2014. The project's Principle Investigators are Profs. B. Notaros and V. N. Bringi from the CSU Department of Electrical and Computer Engineering. The high resolution snow particle images obtained by the Multi-Angle Snowflake Camera (MASC; MASC), developed at the University of Utah, are a key element in the investigation. The three dimensional hydrometeor reconstructions developed from the MASC images will provide the framework for calculations of microwave backscatter fields on a particle by particle basis. These calculated radar fields will be compared to dual polarization observations collected by the CSU-CHILL and NCAR S-Pol radars. This article provides an overview of the ground-based instrumentation that has been assembled for this project and some "first look" data collected on 15 November 2014.
Easton Valley View Airport site
In August, 2014 efforts were made to identify a location where the MASC and its supporting precipitation sensors could be installed at close (less than 15 km) range to the CSU-CHILL radar. This short range would minimize the vertical separation between the center of the radar sampling volume and the surface-based instrumentation. Short radar range also improves the cross-polar signal to noise ratio, allowing usable Linear Depolarization Ratio (Ldr) data to be collected at the low reflectivity levels that are typical of snow. The Easton Valley View Airport located ~13 km south-southeast of the CSU-CHILL radar was found to provide a site where minimal beam blockage occurred at low elevation angles. (The airport owner was also quite interested in hosting the MASCRAD instrumentation). To reduce the effects of wind upon the precipitation samples collected by the ground-based sensors, CSU ECE personnel constructed a 2/3 scale DFIR (Double Fence Intercomparison Reference) wind screen for the ground instrumentation site at the Easton Valley View Airport in October, 2014:
In addition to the MASC, a 2DVD video disdrometor 2DVD and a Pluvio 200 Pluvio weighing-type precipitation gauge were also installed inside the wind screen: (Dr. Walt Petersen made the 2DVD and Pluvio available to MASCRAD from NASA's equipment inventory).
The following picture provides a close-up view of the CSU MASC installation at the Easton Airport:
NWS KFTG 0.5 degree elevation angle reflectivity loop.
Some initial coordinated MASC - CSU-CHILL data collection efforts were done when periods of light snow occurred during the mid-day hours of Saturday, 15 November 2014. The following image loop was made from reflectivity data recorded by the NWS KFTG radar during a portion of the event. The PPI sweeps were made at 0.5 degree elevation angle at time intervals of ~ 10 minutes:
MASC particle image and CSU-CHILL RHI data
An image selected from one of the MASC cameras at 1718:49 UTC is shown below. The snow particle is composed of an aggregation of a number of smaller planar ice crystals. The resultant composite ice / air particle has very low bulk density and an irregular shape.
CSU-CHILL RHI scan over the Easton Airport at approximately the same time as the particle image shown above. As height decreases towards the ground in the Easton area, reflectivity increases while differential reflectivity diminishes from ~ +4 dB to ~ 0 dB. These radar patterns probably occur as the fairly pristine, quasi-horizontally-oriented, ice crystals at echo top undergo collisions and aggregations during their descent towards the surface. This collision process produces many aggregated particles near ground level. These irregularily-shaped, low density aggregates also generate very low (~ -35 dB) Ldr levels.
Subsequent MASCRAD data sets, including additional information from the NCAR's S-Pol radar and a portable sounding system, will be collected during the remainder of the winter months. The detailed 3D snow particle structures developed from the MASC images will allow accurate calculations of their microwave backscattering characteristics.