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Question about radar detection range:

Scenario - SS radar (Decca Series), Range 48nm vs. Low missile contact (not a small missile) RCS 126

Result - I've not gotten a radar contact after 6 test runs, but get visual contact at 1-5 nm depending on time of day (visibility).

Can someone explain all the dynamics that are happening here to prevent the Decca from detecting the low flying missile?

Also, clarify the differences between SS, AS, AS/SS, and HF/3D radars. From reading the Harpoon rules (1989 version) SS detect Surf/Low, AS detect Med+, AS/SS detect Med+ and 10% max vs Surf/Low, HF/3D detect Med+ and out to radar horizon vs. Surf/Low.

I used the HC Radar RCS v6 spreadsheet and plugged in RCS 126 and radar range 48 and get: Plane/Missile 12.88nm, Land Unit 3.75nm, and Ship .39nm. Didn't you create this spreadsheet, Tony? Anyway, like to understand what's going on with this scenario and bit of the under the hood mechanics of radar detection. Thanks.

ORIGINAL: miller7219
Question about radar detection range:
Scenario - SS radar (Decca Series), Range 48nm vs. Low missile contact (not a small missile) RCS 126
Result - I've not gotten a radar contact after 6 test runs, but get visual contact at 1-5 nm depending on time of day (visibility). Can someone explain all the dynamics that are happening here to prevent the Decca from detecting the low flying missile?

You're using a surface search (SS) radar to try and detect an airborne target.

I have raised these questions before, in the harpgamer forums.

(http://harpgamer.com/harpforum/index.php?showtopic=3534)

A harpgamer account may be necessary to view that.

Unfortunately, I didn't get any responses.

**************************

<extract from above-mentioned post> :

I wish to raise some issues about radar, in particular, regarding the differences between surface search and air search radar and the consequences thereof, ...

Please feel free to challenge or refute any aspect of the content. I am not sensitive in that way. I seek the truth.

According to the Harpoon documentation (eg. the Help files), a SS radar is a radar that can detect units at vertical elevations ranging from the sea surface to low altitude, and an AS radar is a radar that can detect units at vertical elevations of medium or higher altitude. In some cases (generally at very short ranges), these radars extend into the other region.

It seems to me that there could be 2 reasons why a radar would only work in one of these regions. One is that special characteristics might be needed for the radar to distinguish a desired contact from “ground clutter”. The other is that the radar needs to be pointed in the right direction.

Being a part of the electromagnetic spectrum, radio waves travel generally in straight lines. Refractive effects tend to be generally irrelevant for radio waves in air, and gravitational effects need not concern us here.

The immediate question is whether the radar emitter and receiver emit and receive in all directions, so that the outgoing wavefront has the form of a sphere, or whether there is a vertical restriction, so that the outgoing wavefront has the form of a cone or something more restricted. For example, if a radar emits radiation only at angles above the horizontal, then, regardless of the vertical elevation of the radar, it cannot function as a SS radar. On the other hand, if the radar emits radiation only at angles below the horizontal, then, ignoring the issue of ground clutter, that radar may function as either a SS or an AS radar, depending on a variety of different factors.



I hope that someone can shed some light on this issue. Based on where that discussion goes, I will have more to say.

There are important consequences to the AS/SS classification. Most obviously, if an enemy unit has only one type of radar, then you may be able hide your units from it in the vertical dimension. For example, many fighters have only an AS radar. Suppose that such an enemy fighter is chasing one of your helicopters. The helicopter can neither fight nor flee (with some exceptions – eg. a Sidewinder-armed SuperCobra might be able to take on a Yak-38). So the helicopter is dead? Not necessarily! If we accept the definition in the <third> paragraph, the helicopter should drop to low or VL altitude (and flee, of course), and the fighter will have difficulty locating it. On the other hand, many aircraft have only a SS radar. If we accept the definition in the <third> paragraph, you will be able to sneak up on these aircraft at medium or higher altitude.

In this particular instance Brad gets the gold star for his abbreviated answer, HCE SS radars can only detect aircraft at VLow altitude. Unrelated to the current discussion, air search radars can detect surface contacts at 5% of the radar's air range (with an extra strange caveat that says height finding radars can't do this). It may actually be saying that height finding air search radars can detect surface contacts at full range, something for someone to test [:)].

Anyway, other factors in general...

Radar is only checked every 30 seconds, that means a missile might travel thru the entire detection envelope before the radar routine is even run.

Don't forget the radar percentage chance of detect, few of the radars have a PD over 70% meaning that at least 30% of the time even if range as listed in the RCS spreadsheet (yes, I created it, and I think the download mentions that the ranges listed are under otherwise ideal conditions) says a detect could happen, it might not; not to mention weather effect).

So radar detects are only done once every 30 seconds and there is a good chance you'll get a bad die roll and have to wait another 30 seconds to try again and pretty soon you can have a really bad day and not detect the bad guys.

ORIGINAL: VictorInThePacific
I have raised these questions before, in the harpgamer forums.
(http://harpgamer.com/harpforum/index.php?showtopic=3534)
A harpgamer account may be necessary to view that. Unfortunately, I didn't get any responses.

Firstly, I never before noticed your post until you pointed it out. Sorry about that. [:(] And, secondly, iirc, at the time you posted it (15 January 2009), the beta section was only accessible to beta testers. If Tony's reply doesn't flesh it out for you, just holler.

Suppose that such an enemy fighter is chasing one of your helicopters. The helicopter can neither fight nor flee (with some exceptions – eg. a Sidewinder-armed SuperCobra might be able to take on a Yak-38). So the helicopter is dead? Not necessarily! If we accept the definition in the <third> paragraph, the helicopter should drop to low or VL altitude (and flee, of course), and the fighter will have difficulty locating it.

Thats possible, though at short ranges you might also be spotted visually, irrespective of what kind of radar your foe is using.

ORIGINAL: TonyE
In this particular instance Brad gets the gold star for his abbreviated answer, HCE SS radars can only detect aircraft at VLow altitude.

I endeavour never to be accused of being long winded. [:D]

ORIGINAL: TonyE
...Radar is only checked every 30 seconds, that means a missile might travel thru the entire detection envelope before the radar routine is even run...

[font="Tahoma"]From a reality standpoint, I would say that is a rather long time! Realizing the GE must traverse a lot of code and data each second, I would think that detection would be given more priority? I would almost be willing to opt for slower performance in another area.[/font]

ORIGINAL: RA5C

ORIGINAL: TonyE
...Radar is only checked every 30 seconds, that means a missile might travel thru the entire detection envelope before the radar routine is even run...

[font="Tahoma"]From a reality standpoint, I would say that is a rather long time! Realizing the GE must traverse a lot of code and data each second, I would think that detection would be given more priority? I would almost be willing to opt for slower performance in another area.[/font]

Can't quite say that I'd agree with more checks and greater frequency of checking, either. Having played H3, I get the impression that the detection frequency is very high for that game (almost 1:1?). Of course, I never seen the actual formulae or source code to verify the frequency of detection rolls but, during game play and testing, contacts seem to appear at the exact same range every time.

This means that the sporadic checking in HCE sometimes allows an enemy interceptor to get close enough to an AEW plane to kill it. This would never happen in H3 as they are always detected at max. Maybe 30 seconds is a bit high, but it does allow for more randomness than something that seems to roll for detection every single second.

ORIGINAL: hermanhum
This means that the sporadic checking in HCE sometimes allows an enemy interceptor to get close enough to an AEW plane to kill it. This would never happen in H3 as they are always detected at max. Maybe 30 seconds is a bit high, but it does allow for more randomness than something that seems to roll for detection every single second.

[font="Tahoma"]I'll take your word it works differently in H3 but I am interested in HCE. I would think that increasing to once every fifteen seconds would improve performance by 100%. Again, I'm speaking in regards to reality vs. capability of the GE/A.I.[/font]

ORIGINAL: TonyE

In this particular instance Brad gets the gold star for his abbreviated answer, HCE SS radars can only detect aircraft at VLow altitude. Unrelated to the current discussion, air search radars can detect surface contacts at 5% of the radar's air range (with an extra strange caveat that says height finding radars can't do this). It may actually be saying that height finding air search radars can detect surface contacts at full range, something for someone to test [:)].

Anyway, other factors in general...

Radar is only checked every 30 seconds, that means a missile might travel thru the entire detection envelope before the radar routine is even run.

Don't forget the radar percentage chance of detect, few of the radars have a PD over 70% meaning that at least 30% of the time even if range as listed in the RCS spreadsheet (yes, I created it, and I think the download mentions that the ranges listed are under otherwise ideal conditions) says a detect could happen, it might not; not to mention weather effect).

So radar detects are only done once every 30 seconds and there is a good chance you'll get a bad die roll and have to wait another 30 seconds to try again and pretty soon you can have a really bad day and not detect the bad guys.

This is a situation where reality and game mechanics contradict each other.
A/S radars have long scan rates (time it takes to perform a 360 degree scan) due to the requirement to receive a echo from greater range. S/S radars have short scan rates, sometimes under a scan a second.
It would much more viable to detect a missile with a radar that has a short scan rate and set to detect doppler shift in target (MTI in the USN) than to trust a long range radar with a long scan rate. This is especially true with short range missiles or missiles fired from short range.
One Radar not properly modeled in the game I feel is the MK-92 FCS, it is a SS/AS with a very short scan rate; it's primary purpose is to detect short range missile launches and engage them.

To check for airborne targets once every 30 seconds is to basically waste 29 scans is precision detection system.
But if the game mechanics cannot model it, then for the sake of the game the radar cannot properly be modeled.

ORIGINAL: makobyte
This is a situation where reality and game mechanics contradict each other.

I think perhaps you misunderstand the extent to which HCE attempts to model radar. Real life radar function, as you've intimated, is considerably more complex. HCE does not model scan rate, just like it doesn't model beamwidth; beam patterns; pulse amplitude, duration, period; PRF; etc, etc. Heck, it doesn't even model the difference between CW Doppler, pulse Doppler, phased array, etc. I could go on and on. Its a simple model designed to produce a simplified result.

One Radar not properly modeled in the game I feel is the MK-92 FCS, it is a SS/AS with a very short scan rate; it's primary purpose is to detect short range missile launches and engage them.

The Mk 92 FCS is not modeled in HCE at all. In fact, it doesn't model fire control radars at all, generally. (The DB that comes with the demo does contain FC radars, but they do not really have any FC function, and the DB that comes with the full version of HCE dispenses with them (for the sake of extra room).

ORIGINAL: CV32

ORIGINAL: makobyte
This is a situation where reality and game mechanics contradict each other.

I think perhaps you misunderstand the extent to which HCE attempts to model radar. Real life radar function, as you've intimated, is considerably more complex. HCE does not model scan rate, just like it doesn't model beamwidth; beam patterns; pulse amplitude, duration, period; PRF; etc, etc. Heck, it doesn't even model the difference between CW Doppler, pulse Doppler, phased array, etc. I could go on and on. Its a simple model designed to produce a simplified result.

One Radar not properly modeled in the game I feel is the MK-92 FCS, it is a SS/AS with a very short scan rate; it's primary purpose is to detect short range missile launches and engage them.

The Mk 92 FCS is not modeled in HCE at all. In fact, it doesn't model fire control radars at all, generally. (The DB that comes with the demo does contain FC radars, but they do not really have any FC function, and the DB that comes with the full version of HCE dispenses with them (for the sake of extra room).

WOW! Thanks for the info. My estimates about Harpoon CE was totally off.
I forget that on my "modified" version of Harpoon IV that we used on the ship, we incorporated a lot of "house rules" that enhanced realism and accuracy in the weapons and sensors. [:'(]

Although a little aggravating for a person with naval experience, it is a good introduction to naval tactics and strategy. [:)]

I will try to tailor my comments to be more in line with the product description rather than my own interpretation of what the product should be. [8D]

ORIGINAL: makobyte
I will try to tailor my comments to be more in line with the product description rather than my own interpretation of what the product should be. [8D]

Nudge nudge, WishList and come chat with us on IRC.

ORIGINAL: TonyE

Nudge nudge, WishList and come chat with us on IRC.

Tony likes someone to stand over him & crack the whip, it seems. [:)]

ORIGINAL: makobyte

WOW! Thanks for the info. My estimates about Harpoon CE was totally off.

I forget that on my "modified" version of Harpoon IV that we used on the ship, we incorporated a lot of "house rules" that enhanced realism and accuracy in the weapons and sensors. [:'(]

If additional sensor flags are of interest to you, you can take a look at the ANW side of things. The database allows the following flags to be set for radar:

Pulse Radar
Pulse Doppler
Continuous Wave
FM Continuous Wave
Frequency Agile
Frequency Diversity
Pulse Compression
Phased Array Radar

I don't know which ones actually work and which ones don't, nor what effect they supposedly have. (There are plenty of flags available in ANW databases that produce no effect whatsoever.)