Introduction to NEXRAD Anomalies & Artifacts

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INTRODUCTION TO NEXRAD ANOMALIES

While NEXRAD is the most advanced radar system currently in use for acquiring data about the weather, it is susceptible to various types of errors and interference. In addition to mechanical and electrical failures, calibration and alignment problems, NEXRAD imagery is brought to us as the result of a computer taking the responses from the radar and passing it through algorithms to produce the image we see. In addition to airborne anomalies (i.e, things that are really in the air but are not of interest, such as dust, pollen, birds), the software algorithms can come up with very spectacular images when it receives data from the radar that isn't contemplated by the algorithm--such as the data produced from an out-of-alignment radar or from a radar that is suffering part failure.

These errors and interference manifest themselves on NEXRAD radar images as "anomalies"--in other words, a "deviation or departure from the normal or common order, form, or rule." In short, these anomalies appear on NEXRAD images even though there isn't actually anything there, or what is there is not of interest (insects, etc.).

The following anomalies are specifically known to exist. Please note that while some of the names given to anomalies are often used in the field (due to the name being descriptive of the anomaly), some of the names were made up by me. Most anomalies don't have specific names so all we do is give them names that help us identify and categorize them.


Starbursts
Chaff
Low-Level Birds
Bird Migration

Sunburst
Nuclear Blast
Spokes
No Radar

Porcupine
Modified Blast
Three Body Scatter
Web

AP
Ground Clutter

Typical Soruces:

  1. NEXRAD Equipment Failure
    • AGC problems: Problems with the automatic gain control. The AGC allows the radar to automatically "fine-tune" its sensitivity to maximimze the useful returns and minimize the undesired anomalies. When this function starts to fail, the radar imagery can become very surprising. (Source).
    • Receiver Failure: This occurs when the radar's receiver actually fails, or starts to fail. Obviously the radar cannot produce a reasonable image when it is incapable of accurately receiving the echos returned from the objects it is monitoring.
  2. Three-body scattering: This occurs primarily when there is large hail forming in the cloud. Since the hail is so reflective, a significant amount of radar energy is scattered towards the ground, reflects off the ground, and then again reflects off the hail before returning to the radar. This results in a Three-body scattering "spike" along the same radial. (Source).
  3. Anomalous Propagation (AP): This is caused primarily in very stable atmospheric conditions (clear, calm nights) and causes the radar beam to be directed into the ground resulting in a grouping of strong echos far from the radar site.
  4. Interference: This typically involves radio frequency interference from one or more of the following sources.
    1. Solar: The sun radiates energy at all wavelengths, including that used by NEXRAD. When pointed directly at NEXRAD (generally at sunrise and sunset) it can provide a "beam" of energy that appears to radiate out from the NEXRAD site towards the rising or setting sun.
    2. Ground Based Radars: Other ground-based radar operated by the FAA, Department of Defense, or others may interfere with and cause anomalies and artifacts on NEXRAD imagery.
    3. Aircraft: Aircraft may cause anomalies if their on-board radars are pointed roughly at a NEXRAD site.
    4. Wireless networks: Wireless networks use radio frequency and may cause interference with NEXRAD if located close enough.
    5. Cable TV: Cable TV may, in some cases, interfere with NEXRAD.
    6. Cell Towers: Cell towers may interfere with NEXRAD due to the fact that they emit radio frequency energy. This is especially true when the cell tower is relatively close to the NEXRAD site.
    7. Other radio transmissions: Any radio transmitter may potentially interfere with NEXRAD if its wavelength is close enough to that used by NEXRAD, or if it emits harmful interferece on wavelengths used by NEXRAD.
Anomaly Studies

In the course of investigating NEXRAD technologies and debunking the NEXRAD conspiracy theory hoax, I engaged in the following studies:

  Reno Anomaly
  Billings Anomaly
  North Platte Anomaly
  Montana Anomaly

Sources: