Guest Article by Peter from DCAF(Digital Coalition Air Force)
The DDD: The Detailed Data Display screen itself shows either only radar return data or radar returns, and nothing else. How radar information is displayed on the DDD is contingent on radar modes, such as pulse, pulse doppler, single target track, and IFF sub modes.
When in pulse search mode, the DDD represents radar returns in relation to azimuth and range. Like all other DDD modes, azimuth is represented in degrees from the nose, represented by the bottom scale. Range is correlated by the middle left and middle right scales, with tick marks breaking the scale into fifths. The RIO can change the range scale via the range buttons at the top of the DDD instrument panel from 5 to 200 nautical miles.
The image below pulse search mode set to fifty nautical miles. By correlating the azimuth and range scales, the radar return(represented by the black brick) is approximately 38° to the right of the nose, and 30nm.
The following image shows the range scale set to 100nm. In this instance, the radar return is 47° to the right, and approximately 24nm.
Like in any radar search mode, a white bar will sweep left and right on the DDD. This is an azimuth representation of the antenna’s train angle(how much the radar is pointed left or right of the fighter’s nose).
By default, the RIO should set the PULSE GAIN knob to NORM to provide the best radar returns. However, when ground clutter is a factor(i.e. the fighter is attempting to lock a lower altitude target that is over land), the RIO may manually adjust the PULSE GAIN knob to filter it out.
In pulse search, radar returns may be visually fainter than that seen on pulse doppler. It is recommended to rotate the ERASE knob counter-clockwise(such that it does not fade from the DDD as quickly), and rotate the PULSE VIDEO knob clockwise to increase the visual intensity of the return(and thus be easier to spot on the DDD).
Pulse Doppler Modes
In a pulse doppler mode, the DDD display shows radar returns in azimuth vs. closure rate relative to the ground. In essence, the DDD shows whether radar returns are approaching faster or slower than a fixed point towards the fighter.
In the image above, the F-14(fighter) is approaching a fixed point on the coastline(circled) at 450 knots ground speed(GS). Further inland, a Flanker(target) is flying towards the fighter at 600 knots ground speed(GS). This means that the fighter is closing at 450 GS towards the fixed point, the target is closing at 600 GS towards the fixed point, and thus the closure between fighter and target is 1050 GS.
This is how the instance above would be visualised on the DDD:
In this instance, the fighter, fixed point, and target have been superimposed over the DDD. Like pulse, azimuth remains the same. However, the closure rate is represented via the leftmost scale on the DDD, with the tick mark representing 600 knot increments.
A radar return(target) with a positive value on the closure rate indicates that it is approaching the fighter faster than a fixed point between them. A radar return with a negative value on the closure rate indicates that it is approaching(and in some instances opening) the fighter slower than a fixed point between them.
The image above reveals that the target has a closure of approximately 600 GS greater than that of the fixed point, and while ownship (fighter) is not represented on the DDD, one can visualise its closure to the fixed point. By knowing the fighter’s ground speed and reading the DDD, on can discern a closure rate of approximately 1050 GS between the fighter and target. While in controlled flight, the fighter can never have a closure rate greater than 0 on the DDD, and instead can only be visualised in the negative closure rate range. In example, should the fighter accelerate to 900GS, one would visualise the contact to be aligned around -900 on the closure rate scale.
Changing the ASPECT switch to the left of the DDD shifts the closure rate scale by 600 knots up and down, allowing the RIO to view radar returns with extreme positive and negative closures. Additionally, this changes the range gates of the pulse doppler filtering of the radar, meaning any returns outside of the closure rate scale will not be detected/shown.
|NOSE||-600 to 1800|
|BEAM||-1200 to 1200|
|TAIL||-1800 to 600|
Pictured below is the same example as before, with aspect changed from nose, beam and tail respectively:
For a more in-depth look into the DDD in Pulse Doppler, check out Karon’s article: Detailed Data Display in Pulse Doppler Mode. The article discusses the role of the Main Lobe Clutter switch, as well as the Zero Doppler Filter.
Depending on interest, I’ll look to draft an article on the DDD and IFF, and STT locks on the DDD.