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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.
Typical Soruces:
- 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.
- 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).
- 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.
- Interference: This typically involves radio frequency interference from one or
more of the following sources.
- 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.
- 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.
- Aircraft: Aircraft may cause anomalies if their on-board radars are pointed
roughly at a NEXRAD site.
- Wireless networks: Wireless networks use radio frequency and may cause
interference with NEXRAD if located close enough.
- Cable TV: Cable TV may, in some cases, interfere with NEXRAD.
- 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.
- 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:
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