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GPM Ground Validation Second Generation Airborne Precipitation Radar (APR-2) GCPEx Table of Contents
The Second Generation Airborne Precipitation Radar (APR-2), along with the Conical Scanning Millimeter-wave Imaging Radiometer (CoSMIR), flew aboard NASA'S DC-8 during the Cold-season Precipitation Experiment (GCPEx). Both APR-2 and CoSMIR served as an airborne simulator for the GPM core satellite. The APR-2 is a dual-frequency (13 GHz & 35 GHz), dual-polarization, Doppler radar system. It has a downward looking antenna that performs cross track scans, covering a swath that is +- 25 to each side of the aircraft path. The GCPEx APR-2 data set, collected over Ontario from January to February 2012, is available in HDF (Hierarchical Data Format) from the GHRC. CampaignThe GPM Cold-season Precipitation Experiment (GCPEx) occurred in Ontario, Canada during the winter season of 2011-2012. GCPEx addressed shortcomings in the GPM snowfall retrieval algorithm by collecting microphysical properties, associated remote sensing observations, and coordinated model simulations of precipitating snow. These data sets were collected to aid in the achievement of the over arching goal of GCPEx which is to characterize the ability of multi-frequency active and passive microwave sensors to detect and estimate falling snow. During GCPEx, the APR-2 was flown on NASA's DC-8 aircraft. The DC-8 made a total of 14 flights over the period of January 11- February 25, 2012. For GCPEx, the APR-2 provided aerial insights into snowfall processes and physics. Further details on GCPEx are available at http://gpm.nsstc.nasa.gov/gcpex. Information on the Global Precipitation Measurement (GPM) mission is available at http://pmm.nasa.gov/GPM. Additional campaign collections containing APR-2 data can be found at http://ghrc.nsstc.nasa.gov. Instrument DescriptionThe APR-2 system includes a real-time pulse compression processor, a fully-functional control and timing unit, and a very compact LO/IF module, all of which could be used in space borne applications. The cylindrical reflector antenna and linear feed array for the space borne PR-2 have been replaced by traveling wave tube amplifiers (TWTAs), front-end electronics, and an offset parabolic reflector antenna with mechanical scanning. The APR-2 operational geometry is as follows: the instrument looks downward and scans its beam across-track, with each scan beginning at 25 degrees to the left of nadir and ending at 25 degrees to the right. The APR-2 uses the same scanning antenna reflector as that used for the Airborne Rain Mapping Radar (ARMAR), which consists of a 0.4 m offset reflector antenna with a mechanically scanned flat plate. The APR-2 antenna feed is a dual-frequency feed (13.4 and 35.6 GHz) and the aperture at 35.6 GHz is under-illuminated to provide matched beams at the two frequencies. This choice results in poor Doppler accuracy at Ka-band, but is needed for rain retrieval. Additional information on the development and specifics of the APR-2 system can be viewed at the following Jet Propulsion Lab web site: http://trmm.jpl.nasa.gov/apr.html InvestigatorsStephen Durden Simone Tanelli The data files are HDF (Hierarchical Data Format) and are named with the following convention:
where, Data Format Data files are in HDF (Hierarchical Data Format). The Principal Investigator has provided a Product Handbook which details information concerning data format, missing data, and known issues with the APR-2 data. This data can be read with almost any HDF reader, thus no sample read software is supplied by the data producer. More information about HDF may be found at the HDF group home page. CitationOur data sets are provided through the NASA Earth Science Data and Information System (ESDIS) Project and the Global Hydrology Resource Center (GHRC) Distributed Active Archive Center (DAAC). GHRC DAAC is one of NASA's Earth Observing System Data and Information System (EOSDIS) data centers that are part of the ESDIS project. ESDIS data are not copyrighted; however, in the event that you publish our data or results derived by using our data, we request that you include an acknowledgment within the text of the article and a citation on your reference list. Examples for general acknowledgments, data set citation in a reference listing, and crediting online web images and information can be found at: http://ghrc.nsstc.nasa.gov/uso/citation.html Sadowy, G. A., A. C. Berkun, W. Chun, E. Im, and S. L. Durden, 2003: Development of an advanced airborne precipitation radar. Microwave J., 46(1), 84-98. Haddad, Z. S., J. P. Meagher, S. L. Durden, E. A. Smith, and E. Im, 2006: Drop size ambiguities in the retrieval of precipitation profiles from dual-frequency radar measurements. J. Atmos. Sci.,63, 204-217. Contact InformationTo order these data or for further information, please contact:
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