XSAPR

The X-Band Scanning ARM Precipitation Radar (XSAPR) is an X-band dual-polarization Doppler weather radar. The XSAPR operates in a simultaneous transmit and receive (STAR) mode, meaning that the transmit signal is split so that power is transmitted on both horizontal and vertical polarizations at the same time. The XSAPR transmitter is a 200 kW (peak power) magnetron. The receiver is based upon the Vaisala RVP-900 and runs Vaisala’s IRIS software.

In addition to the first three Doppler moments (reflectivity, radial velocity, and spectral width), the XSAPR also provides differential reflectivity, correlation coefficient, and differential phase. The dual-polarization variables enable estimates of rainfall rates and identification of precipitation types.

Prior to 2025, three XSAPRs surrounded the Central Facility at ARM’s Southern Great Plains (SGP) atmospheric observatory, allowing the use of multi-Doppler velocity retrievals to estimate wind fields. As of 2025, there is one XSAPR at the SGP and one XSAPR at the North Slope of Alaska (NSA) observatory. There is also a second-generation XSAPR (XSAPR2) deployed at the Eastern North Atlantic observatory that has a different transmitter and receiver from the first-generation XSAPRs. The XSAPR2 has a narrower beam width, allowing for more detailed studies of drizzle in a maritime environment.

In addition to original operational a1-level data, XSAPR data are available as b1-level products starting from 2024 at the NSA. Building on the a1-level data, the b1-level products feature improved data quality resulting from extensive analyses and corrections. The data are cross-calibrated to a common point, datastreams are corrected for any operational issues that occurred, and data quality/classification masks and basic derived products are incorporated. For more information, read the published b1-level processing report.

• Radar Doppler
• Radar polarization
• Radar reflectivity