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NPOL: GPM Precipitation Science Research Facility

NASA S-Band Dual-Polarimetric Radar (NPOL)

NPOL is NASA's premier weather radar. It is one of only two mobile S-band dual-polarization radars (the other being NCAR's SPOL). When not being deployed for PMM/GPM field campaigns, it is operated near NASA's Wallops Flight Facility in Newark, MD.

NPOL has a wavelength of 10.65 cm, an operating frequency of 2700-2900 MHz, variable PRF of 500 and 1000 Hz with a 0.95 degree beam width. NPOL can operate with both horizontal and vertical polarization in both simultaneous and alternating modes. The radar has a prime-focus parabolic reflector which is 8.5 m in diameter and is housed on five sea-tainers. When readied for deployment, the entire radar and antenna system is stored within the five seatainers.

The image to the right shows a network of rain gauges and disdrometer deployed in the NPOL domain. All of these instruments are being used to help validate GPM satellite over an area of 0.5 degrees latitude x 0.5 degrees latitude. Click on on the image to see a higher resolution map of the network.

Radar imagery on this page was generated using PyART

Helmus, J.J. and Collis, S.M., 2016. The Python ARM Radar Toolkit (Py-ART), a Library forWorking with Weather Radar Data in the Python Programming Language. Journal of Open Research Software, 4(1), p.e25. DOI:

Latest NPOL Imagery

PPI Images RHI Images

Latest NPOL Radar Animations

Reflectivity [dBZ]Radial Velocity [m/s]Differential Reflectivity [dB]
CorellationDifferential Phase [deg]Specific Differential Phase [deg/km]

Click thumbnails to view animatewd gif!

Latest Quasi-Vertical Profile

A quasi-vertical profile (QVP) is a conical scan at 20.0 degrees elevation. The reflectivity, differential reflectivity, correlation, and differential phase are azimuthally averaged by range bin, and are presented in a height-versus-time format. A height of 10 km is approximately 30 km range from NPOL (see figure). Per Ryzhkov et al. 2016, the temporal evolution of microphysical processes that govern precipitation is a key benefit to this methodology. Through this technique, NPOL will be monitoring characteristics and behavior of the melting layer, regions of dendritic growth, riming, and snow aggregation with high vertical resolution. Comparisons with vertically looking remote sensors such as the Micro-Rain-Radar (MRR) and the GPM Dual-Frequency Precipitation Radar (DPR) will be performed for validation within the atmospheric column.
More QVP info:

Radar Calibration Information

BirdBath Scan [Zdr cal]

Enlarge Birdbath

Animated GIF

Relative Calibration Adjustment

Latest Daily RCA Values

Latest Hourly RCA Values

More RCA info:

Pointing Accuracy

The pointing accuracy of the NPOL antenna is monitored by analyzing daily SunCal scans. These plots are generally run twice daily, once in the morning and the other in later afternoon, which provides additional detail on the level of the dish.

The plots to the right show the time series of estimated pointing error, as determined by the SIGMET SolarCal utility for Azimuth (top) and Elevation (bottom). Click on the image to see an expanded image. The blue triangles represent the AM scans, while the red triangles represent the PM scans. Ideally, these would be centered +/- some delta around zero, so an offset indicates a possible actual pointing issue.

More SunCal info

Absolute Calibration

Absolute Calibration: GPM uses both Self-consistency and comparisons between disdrometers and the radar to provide estimates of the absolute calibration. Click here to see the frequently updated NPOL Bias Table.

Data Availability

Use the pull down menu to display a monthly data availability plot similar to the one to the left of this panel.
  • Monthly Daily Availability Plots

  • Use the pull down menu to display a yearly data availability plot.
  • Yearly Daily Availability Plots
  • NPOL Precipitation Events

    Use the pull down menu to display a monthly NPOL precipitation event plot similar to the one to the left of this panel.
  • Monthly NPOL Precipitation Event Plots

  • Use the pull down menu to display a yearly NPOL precipitation event plot.
  • Yearly NPOL Precipitation Event Plot
  • Notes on the Hydrometeor Identfication Images

    The HID product is generated using software provided by Colorado State University and is based on the continued work of Dolan et al. (2013). The classifications are:
    UC Unclassified
    DZ Drizzle
    RN Rain
    CR Ice Crystals
    DS Dry Snow
    WS Wet Snow
    VI Vertically-aligned Ice
    LDG Low-density Graupel
    HDG High-density Graupel
    HA Hail
    BD Big Drops

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