OLYMPEX: A GPM Ground Validation Campaign on the Olympic Peninsula in the Pacific Northwest

The Core satellite of the Global Precipitation Measurement (GPM) Mission was successfully launched at 1837 UTC 27 February 2014 from the Japanese Space Agency (JAXA) Space Center on Tanegashima Island, Japan. Aboard the satellite is the first space-borne Ku/Ka band Dual Frequency Precipitation Radar (DPR) and a passive microwave radiometer, with channels ranging from 10-183 GHz. Both these instruments are currently operating on the GPM Core and are collecting real-time precipitation data. The primary objective of the Core satellite is to measure rain and snow globally, determine its 3D structure, and act as the calibration satellite for a constellation of GPM passive microwave satellites. The core satellite will be especially valuable in areas lacking surface observations or ground-based radar. The GPM satellites will need to be able to detect both solid and liquid precipitation in a wide range of intensities, locations and regimes. In order to identify and understand uncertainties in the GPM measurements and to assess how remotely sensed precipitation can be applied to a range of data applications (e.g. determining storm structures and monitoring runoff and flooding events), ground validation (GV) field campaigns are crucial. As such, the Olympic Mountains GV Experiment (OLYMPEX) is planned for November 2015 – February 2016.

The Olympic Peninsula in the northwest corner of Washington State is an ideal location to conduct a GV campaign. It is situated within an active mid-latitude winter storm track and receives among the highest annual precipitation amounts in North America, ranging from over 2500 mm on the coast to 4000 mm in the mountainous interior. In one compact area, the Olympic peninsula ranges from ocean to coast to land to mountains. It contains a permanent snowfield and numerous associated river basins. This unique venue will enable the field campaign to monitor both upstream precipitation characteristics and processes over the ocean and their modification over complex terrain.

The scientific goals of the OLYMPEX field campaign include physical validation of satellite algorithms, precipitation mechanisms in complex terrain, hydrological applications, and modeling studies. In order to address these goals, a wide variety of existing and new observations and instrumentation are planned. These include an in situ surface observing networks of meteorological stations, rain and snow gauges, surface microphysical measurements, and snowpack surveys. Surface-based remote sensing instrumentation will include the existing coastal radar at Langley, Washington, and planned additional radars such as the NASA N-Pol S-Band dual-polarimetric and NASA Dual-Frequency Dual-Polarimetric Doppler (D3R) scanning radars for PPI and RHI scanning over the west slopes of the Olympics, and other mobile vertically-pointing radars. Several instrumented aircraft are likely to participate. The NASA DC-8 will be equipped with a Ka/Ku band dual-frequency radar and passive microwave sensors that simulate those on the GPM Core satellite. The University of North Dakota Citation will measure in situ microphysics. The aircraft measurements will determine upstream thermodynamic and moisture conditions, sample particle types and sizes for comparison with those employed in the satellite algorithm, and act as a proxy for the satellite itself. The ground-based measurements will test how well the satellite proxy measurements determine the rain and snow over complex terrain.