Makers developing radars that remember

 - January 31, 2007, 5:55 AM

The next generation of airborne weather radars won’t just see the storms, they will remember what they have scanned and store that information in a computer database. By keeping a continuous record of radar returns ahead of the aircraft– culled from a series of quick “snapshots” taken at varying tilt angles and distances–the multiscan weather radars of tomorrow will greatly reduce workload and, for the first time, provide flight crews with three-dimensional views of storms and turbulence, according to radar makers.

Rockwell Collins and Honeywell recently introduced airborne weather radar systems that use the database storage and multiscanning techniques for the air-transport market, and both companies say versions for business aviation aren’t far off. The keys to the Collins and Honeywell radars are their abilities to scan and store weather information in their databases and to eliminate ground clutter–automatically and, their developers claim, extremely effectively.

Both the Collins WXR-2100 multiscan radar and the Honeywell RDR-4000 display storm returns without the need for traditional tilt and gain inputs from pilots. But each achieves this goal in a different way. The key to the WXR-2100’s operation, according to Collins, is the system’s ability to look down toward the bottom of the reflectivity portion of a thunderstorm and eliminate ground clutter using digital signal processing techniques and patented computer algorithms. The Honeywell radar, on the other hand, uses the terrain database from the enhanced ground proximity warning system to judge where ground clutter should be removed from the radar picture.

Collins WXR-2100
Put the WXR-2100 in its fully automatic mode and pilots can be assured the weather information they are receiving is just as good as anything radar education guru Archie Trammell could coax out of a traditional radar system, Collins engineers claim. Besides simplifying crew training requirements, the WXR-2100’s automatic mode reduces workload because the radar’s computer, not the crew, sets the tilt and gain. All the pilots need to do is choose the range, which is claimed to be as much as 320 nm, and the radar’s computer does the rest.

Traditional radar looks directly below the aircraft to detect storms and then follows the curvature of the earth out to the radar’s maximum range. Conversely, multiscan radars emulate an ideal radar beam by merging information from different radar scans into a single weather picture. In the case of the WXR-2100, multiple antenna scans are performed, each optimized for a particular region in front of the aircraft (short-, medium- or long-range weather) by automatically adjusting tilt and gain. The computer merges the data into a digital picture, refines the image and eliminates ground clutter using suppression algorithms that take into account the earth’s curvature.

Each multiscan cycle takes about eight seconds to complete in automatic mode and a little more than 11 seconds in wind-shear mode. The radar antenna makes a series of quick passes ahead of the aircraft, storing all the data it collects in memory. The advantage of storing a digital presentation of radar returns, say developers, is that as an aircraft moves along its route of flight or makes a turn, the image on the radar display can be rotated without the need for a new radar sweep. This frees the antenna to perform multiple functions while still displaying weather data stored in the computer’s database.

The WXR-2100 also automatically adjusts weather detection parameters for variations caused by time of day, time of year and geographic position and uses “radar threshold” technologies to adjust the radar returns to more accurately display actual thunderstorm threats, according to Collins. The system also features so-called overflight protection, providing crews with the ability to avoid inadvertent penetration of thunderstorm tops, one of the leading causes of unexpected encounters with turbulence. A future enhancement to the system will include measurements of storm tops and information about storm cell development, Collins said.

Honeywell RDR-4000
Introduced last summer, the RDR-4000 employs what Honeywell calls “3-D volumetric scanning” to provide a more complete picture of the weather than traditional radar provides. Similar to the Collins multiscan radar, the RDR-4000 searches the sky from the ground to 60,000 feet, creating a three-dimensional database of information, which is analyzed by a computer. The RDR-4000 then provides a traditional picture of radar returns in addition to a vertical profile view of weather, showing a sideways-looking vertical “slice of weather.” This “real-world view” can be aligned along the aircraft’s current direction of flight, a specified direction off the nose or along the intended flight path entered in the FMS.

Another area where the RDR-4000 differentiates itself is in the way it eliminates ground clutter. Rather than using computer algorithms alone to determine which radar returns are the ground and which are weather, the RDR-4000 uses its internal EGPWS terrain database to ensure that only unwanted ground returns are eliminated from the display. Honeywell asserts this technique provides
a more accurate view of storms than systems that use computer filtering techniques alone.

Besides radar returns, the RDR-4000 can provide forward-looking wind-shear alerting with an antenna as small as 12 inches in diameter, half the diameter required by the current RDR-4B, Honeywell said. That’s small enough for a wide range of business jets and should allow the introduction of the radar beyond airline service (Airbus selected the RDR-4000 for the A380) before long.

As with the Collins radar, users of the RDR-4000 can select fully automatic mode to reduce workload and avoid confusion. In this mode, the radar display shows only relevant weather, taking into account the route and climb/descent profiles entered in the FMS. Also, rather than adjusting antenna tilt angle to have the radar look downward or upward at a certain angle from the airplane, RDR-4000 users can select constant altitude mode to view weather at any given altitude.