Dodging the Weather - With Radar
August 1956 Popular Electronics

August 1956 Popular Electronics Table of Contents Wax nostalgic about and learn from the history of early electronics. See articles from Popular Electronics, published October 1954 - April 1985. All copyrights are hereby acknowledged.

As with nearly things electronic, innovations in radar systems that were ground-breaking a few decades ago are now available commercially at a small fraction of the cost, a much more compact size, and much greater performance and reliability (see SI-TEX T-760 at right). Radar operators during World War II noticed that they were able to detect strong rainstorms demonstrating that signals did not necessarily need a metallic object to be reflected strongly enough to be received and processed. Research began soon thereafter to build radars optimized for detecting weather phenomena. Early weather radars were 'simple' reflective types that indicated distance, height, and speed (by comparing successive samples). Doppler radar was developed next, adding a much greater capability to characterize particular weather systems according to intensity, direction, rotation (hurricanes , tornadoes), composition (ice, snow, rain, etc.), speed (average and gust), and other parameters.

Dodging the Weather - With Radar

Radar picks safe spots amid stormy skies.

Heading for the clouds can be tricky business if you haven't got your feet on the ground. In fact, unexpected weather fronts constitute one of the main hazards of flight.

Collins Radio Company has recently developed an airborne weather radar system that provides immediate indication of the weather ahead. The information is displayed in the form of a weather map showing conditions within a radius of 150 miles and approximately 240 degrees around the nose of the, aircraft. This map-like image on the radar screen shows the location of weather fronts in terms of range and azimuth bearing relative to the position of the aircraft. It identifies areas potentially dangerous to flight, such as thunderheads, hailstorms, or turbulent areas associated with heavy rainfall. With this map as a guide, pilots can investigate aircraft to avoid storms or turbulent areas, usually by detours of five miles or less from the planned flight path.

The weather map is created by the reflection of high-frequency radar waves from rain, hail, snow and ice. When these elements are not present in a cloud structure, energy is not reflected and hence no warning weather map is displayed on the cockpit indicator. Such "empty" clouds can be traversed with little or no difficulty.

To allow aircraft to be piloted safely through thunderstorms, information regarding turbulence, rain, snow and icing conditions must be obtained. Such information is based upon rainfall gradients (i.e., varying rainfall densities at different distances) which can be displayed on the radar screen by a unique circuit.

These rainfall gradients are pictured by insertion of a so-called "iso-echo" circuit, which shows areas of heavy rainfall as dark areas - or black holes within the brighter image of areas with only light precipitation. In this way it is possible for the pilot to spot the more dangerous areas within the cloud formations themselves.

Turbulence is recorded indirectly. Varying degrees of turbulence exist in the areas of heavy rainfall. While turbulence itself cannot be seen on a weather map, it is known to be greatest where the rainfall gradient is highest, i.e., where the pattern is dark. The system may also be used to provide a ground map which gives a visual display of cities, rivers, lakes, shorelines, mountains and other terrain conformations. This ground map serves as an invaluable navigation aid, effectively extending the vision of the pilot during all conditions which restrict visibility.

To enhance reliability, magnetic amplifiers and mineral diodes are used wherever practical since these components have no filaments and thus avoid the possibility of filament failure. In addition, this assures an efficient system with low heat dissipation, low current drain and power demand.

The system can be used with two indicators operating simultaneously. This arrangement offers the advantage that each indicator can be set to a different range, so that both nearby and distant conditions are depicted simultaneously.

Printed wiring is used to provide physical strength and to insure precise placement of components and proper length of leads. Delta Airlines, the first to use this installation, has thereby added another safety factor as well as passenger comfort to its flights.

Radome nose, made of special plastic transparent to microwave radiation with only minimum power loss, is bolted onto the fuselage of Delta airliner housing the first commercial Collins Airborne Weather Radar. With radome removed, you can see antenna at right.

Posted April 6, 2017