Geo-Marine, Inc is pioneering the computer processing of radar targets to distinguish the subtle differences of biological targets and weather displayed in NEXRAD images. This technique was developed to allow the USAF to automatically evaluate thousands of low-level training routes per hour for the presence of birds. Collisions between birds and aircraft can cause thousands of dollars in damage and occasionally the loss of an aircraft or life. Geo-Marine is specially preparing the hourly images shown on this web site. The images have most of the weather suppressed by using unique algorithms. Below is a guide to understanding the resulting images.

Picture 1. Shows a low intensity bird movement close to the radar. When small amounts of bird activity are taking place low to the ground, small rings of returns appear around each radar site. Three radars are used in the Philadelphia region so three small clusters can occasionally be seen. These non-weather related targets can frequently be seen at dawn and dusk when birds are making local foraging and roost flights. They can also occur at other times of the day or night.

Picture 2. Shows a high intensity bird migration. As dusk approaches watch for blooms to grow around each of the radars, migrant birds filling the atmosphere create these blooms. The growth of these blooms can be seen quite clearly in the animated images. Normally bird migration can be seen out to about 64 nautical miles from the radar. If the weather conditions are correct for atmospheric refraction the radar beam can be bent towards the ground and bird migration is seen to the limits of each radars range.

Picture 3. In this image you have a pale blue line we refer to as the "Blue Amoeba" that shows where the weather algorithm has removed the weather. Weather suppression simplifies the imagery by making it easier to understand what is weather and what are potentially bird targets. Current images are showing the "Blue Amoeba" in a darker shade of blue. The name "Blue Amoeba" comes from the way the blue line appears to crawl across the frame in an animation.

Picture 4. Shows low intensity bird activity close to a radar, similar to picture 1 but also includes an adjacent weather system outlined by the pale blue line like in picture 3. Along the edge of the "Blue Amoeba" in the upper right corner is a green area of some weather artifacts that the weather suppression algorithm failed to remove. At the edges of a storm cell the current algorithms find it difficult to decide if targets are birds or weather. This is a rapidly evolving area of technology and improvements are continuously being made to eliminate these errors.

Picture 5. A Low intensity snow front is shown that was not successfully removed by the weather suppression algorithm. The current algorithm uses the vertical distribution of targets in the different elevation scans of the NEXRAD antenna to decide if the targets are weather (reaching up to high altitudes) or birds (within several thousand feet of the earth). Snow, particularly blowing snow can look to the current generation of algorithms like birds as it forms and moves in the lowest elevations of the radar. Improvements to remove these errors will be implemented during the summer of 2000.

Picture 6. Small storm cells. In pictures 3 and 4 the "Blue Amoeba" line extended outside the image. Here small storm cells outlined by the "Blue Amoeba" are completely visible in this small image. The bright red comes from small artifacts of weather that were not fully suppressed. Artifacts of weather are normally in close proximity to the "Blue Amoeba".

Picture 7. Not everything seen on NEXRAD that is not weather are also biological in origin. Sun Spurs are generated when the rising or setting sun shines directly into the radar. The sun is a source of every wavelength of electro magnetic radiation in addition to light, including the 10 cm wavelength that NEXRAD operates. When looking directly at the sun the radar falsely registers returns. If the image was generated at sunrise or sunset it may include one of these lines. A method of suppressing these lines has been successfully tested and will be implemented during the summer of 2000.

Picture 8. Another source of targets that are non-weather and non-biological in origin is Chaff. This is radar decoy material discharged from military aircraft to prevent them from being shot down by missiles. The US military regularly uses chaff in military training. Like snow it is found in the lower atmosphere and the current generation of algorithms can mistake chaff for birds. The distinct slug track pattern will make this easy to suppress in the improvements to be implemented during the summer of 2000.

Recognizing the basic types of echoes seen in the hourly images will help you to understand the radar imagery.