Question: how far out should ship RWR's work?

[DarkFib3r]

I just ran a test to see how detectable a MRK Nanuchka I with active emissions is and how well fjords will hide a unit from radar detection and it has raised some questions. I placed a modern DDG 1000 Zumwalt with a AN/SLQ-32 ESM (500nm ELINT) and a P 960 Storm with a NO/SR-1A RWR (120nm) about 30nm away. Neither unit could pick up the active sensors until they were ~23nm and ~18nm away respectively.

Nanuchka's view:

2023-04-30_21-36-59.png (140.32 KiB) Viewed 364 times

Other's view:

2023-04-30_21-37-50.png (88.05 KiB) Viewed 364 times

My original understanding is that an RWR should be able to detect an emitting sensor at ~twice the range of that sensor. So if the Nanuchka's radar has a 35nm range, any RWR should be able to detect it within ~70nm. At the very least, I would expect that it can detect radars that are returning to their sources, like in my example. Furthermore, a surface based radar essentially has line of sight and that elevations, like fjords, should shield units from those radars.

1. What does the RWR range on a ship actually mean?
2. How far out should a radiating sensor be detectable at?
3. Can ship radars flow over terrain and identify things hiding behind elevations?

[lumiere]

Someone correct me if I said something wrong:

1. DB range value is "theorical" maximum detection range against high-altitude/strong emitter. Please do not think sensor can achieve such performance against low-altitude/weaker emitter.

2. Especially for surface-to-surface detection, because both units are located at seasurface, target must be within radar horizon when checking LOS for radar/ESM detection. I'm not sure the exact value but rule of thumb is 15-25nm range or so (assuming mast hights are 20-130ft).

If you need to detect emitter at further range, you need aerial unit with proper ESM/ELINT sensor (that's why Chinese spy ballon in February flew at 60Kft!).

3. Normally, no. However please note that Titanit/Band Stand radar of Nanuchka is OTH-capable so they can detect target beyond radar horison and ignore LOS interruption caused by terrain.

In your example, Distance between Zumwalt and Nanuchka is about 30nm. It is out of radar horizon of Zumwalt (25nm?), but within Nanuchka's Titanit OTH radar detection range (35nm). So Zumwalt cannot gain ESM detection until it close to within 25nm.

It is good to use LOS tool ("Map Settings - LOS tool" menu) for checking unit sensor LOS.

[Quark73]

2. Especially for surface-to-surface detection, because both units are located at seasurface, target must be within radar horizon when checking LOS for radar/ESM detection. I'm not sure the exact value but rule of thumb is 15-25nm range or so (assuming mast hights are 20-130ft).

If you need to detect emitter at further range, you need aerial unit with proper ESM/ELINT sensor (that's why Chinese spy ballon in February flew at 60Kft!).

3. Normally, no. However please note that Titanit/Band Stand radar of Nanuchka is OTH-capable so they can detect target beyond radar horison and ignore LOS interruption caused by terrain.

In your example, Distance between Zumwalt and Nanuchka is about 30nm. It is out of radar horizon of Zumwalt (25nm?), but within Nanuchka's Titanit OTH radar detection range (35nm). So Zumwalt cannot gain ESM detection until it close to within 25nm.

It is good to use LOS tool ("Map Settings - LOS tool" menu) for checking unit sensor LOS.

I am not an HF/ELINT specialist, but IMHO this can't be the full explanation. Yes the Titanit is an OTH radar an is (should be) capable to detect object behind the horizon. As I understand (acc. DB) it is using a backscatter type OTH radar where the EM wave is reflected by ionosphere. But it still needs the reflection back from the object to detect it. This means acc. radar equation the energy that hits the object is much higher (by orders of magnitude) than the energy that gets back to the radar receiver. Therefore IMHO the Zumwalts ELINT should be capable to pick the Titanit signal up and process it way before the Nanuchka gets an usable signal, even if it is behind horizon.

[DarkFib3r]

Ah, I didn't know that OTH radars did some ionosphere bouncing tricks, so that explain why it could see behind hills and such: it's detecting from a high-ish angle. TIL!

I echo @Quark73: for OTH radars, won't ship-based ELINT detect those especially if there is enough energy to return to the source emitter to elicit a detection? I added an AWACS and it was able to detect the radar emissions of the Nanuchka from hundreds of miles away. If its ELINT gear can detect OTH radar waves from that far away, why can't ship-based ELINT detect these same waves from a closer range?

Thanks for the excellent responses!