Radar in the 21st Century Page 2
|Radar in the 21st Century|
Part 2: Enhance target acquisition and discrimination
By Ben Ellison — March 2002
Radar designers have devised all sorts of tricks to further enhance target acquisition and discrimination. For instance, savvy operators typically switch ranges frequently because a transceiver reconfigures itself for each range, in a sense refocusing its "sight." The longer pulses and slower repetition rate of a desirable larger range may blot out close targets. Modern displays can often be offset to Look Ahead or even in a variable direction (perhaps when operating along a shore) to make best use of a given range’s focus. Some can also zoom into a user-selectable area, displaying the results in a separate window. Most units have an Expand function that overrides pulse length for smaller ranges, thus amplifying the target size, but at the expense of resolution.
New sets from Simrad and Si-Tex offer dual ranges in side-by-side windows, employing a double speed scanner that can feed the display two sets of pulse lengths and repetition rates simultaneously. Several manufacturers also offer optional 3D windows beneath the normal bird’s-eye display. Software interpolates target echoes into images you might see from a high bridge. They look decidedly more realistic than possible and should be treated with caution; apparently their real value is as an advanced form of sea clutter filtering, looking for and emphasizing the peaks of targets.
Doing classic coastal navigation in dark or fog, skippers worked hard comparing radar screen to paper chart–usually with a course track and dead-reckoning position penciled in–to determine which targets were fixed, confirm position, and identify traffic. Range rings helped with the cross referencing, and EBLs (Electronic Bearing Lines), VRMs (Variable Range Markers), and/or a screen cursor could be used to plot identified land features or aids to navigation relative to the vessel, or vice-versa.
These techniques are not completely dead; in fact, a lot of modern machines have added "Floating" EBLs and VRMs useful for certain advanced double-checking exercises. However, GPSs are ubiquitous, and a simple NMEA waypoint sentence can be automatically displayed on a radar as a lollipop icon, both helping to orient the radar to the chart and perhaps identifying a target if your waypoint happens to be a buoy. Even simple GPS heading data–especially now with SA off and WAAS on–can be used to turn the radar image north up or course up. Either mode makes comparison to a chart easier, while also eliminating the confusion of a head-up display on which everything swings relative to your steering.
This article originally appeared in the February 2003 issue of Power & Motoryacht magazine.