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ship radar coverage - 1/11/2020 6:40:20 PM   
anlgzl

 

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Hi all,

Is it possible that a ship can detect an enemy ship which is behind an island with its radar?




thanks in advance

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< Message edited by anlgzl -- 1/11/2020 6:41:06 PM >
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RE: ship radar coverage - 1/12/2020 2:52:39 PM   
Parel803

 

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Normally not if the heigth of the island is higher than the ship. It's a blind spot for radar EM energy. Used by Fast Patrol Boats on rocky coasts. Same the other way around, for ESM. Lower RF's may bend a with the earth curve, so depending on RF's, distances, etc you might get some EM energy.

with regards

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RE: ship radar coverage - 1/12/2020 3:17:27 PM   
Rory Noonan

 

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The Band Stand is an over-the-horizon (OTH) radar that uses backscatter. That's why you can see it

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RE: ship radar coverage - 1/12/2020 4:42:05 PM   
Parel803

 

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Sorry. I'll think about it a little different but that's why its a game.

with regards

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RE: ship radar coverage - 1/12/2020 4:50:11 PM   
anlgzl

 

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Parel803 & apache85 ... Thank you

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RE: ship radar coverage - 2/6/2020 6:52:55 PM   
Blast33


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OTH backscatter at 7.3 Nm is not feasable

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RE: ship radar coverage - 2/7/2020 5:28:14 AM   
Dimitris


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quote:

ORIGINAL: Blast33
OTH backscatter at 7.3 Nm is not feasable


Pray elaborate.

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RE: ship radar coverage - 2/10/2020 3:55:30 PM   
Blast33


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quote:

Band Stand


The Mineral ME system consists of three cooperating systems.
Active, Passive and a data-link.
The complete system operates from D till I-band. (Datalink till active rdr).
-The active radar can't see behind the island. (radar=line-of-sight) with some curving here and there. Which are blocked by the island.
-The passive part must pick up radar signals from the enemy ship (blocked by the island).
-The datalink can provide OTH capability in case of a remote sensor (for example Helicopter).

OTH operate on lower frequencies (see picture).
With a long time between pulses and @ 7.3 km this is

Brochure of the Mineral-ME here
Hopefully this supports my previous (too) short sentence




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RE: ship radar coverage - 2/10/2020 5:43:22 PM   
Parel803

 

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What I remember and it might be incorrect, than I apoligize.
An OTH radar Skywave system is in the RF range of 3–30 MHz.
An OTH radar in the LF & VLF (3-300 KHz) for bending with the earth curve.
Bending with the earth curve start around 3,5 or 3 GHz and down.
An I-band radar is Line-of-sight, radar horizon, depending on other parameters.
OTH radars are big.

A passive radar uses already existing RF signals wich are in the air like radio frequencies. Reading the documentation on this radar it looks like the passive radar part is actually a radar ESM part.

I guess the link systems range are in the same matter determined by its operating frequency

Hope I can help, with regards.

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RE: ship radar coverage - 2/10/2020 5:51:34 PM   
Primarchx


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It's probably important to differentiate between an OTH Backscatter and an OTH Surface Wave system. Their ranges, wavelengths and sensitivities can differ substantially.

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RE: ship radar coverage - 2/10/2020 6:14:55 PM   
Blast33


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quote:

OTH Surface Wave


A Band Stand radar on a Type-54A is very different than these types of radars in size and frequency.
Underneath a short explanation of the difference of OTH-Surface Wave and OTH-Backscattering

Over–The–Horizon Surface Wave (OTH–SW)
OTH-SW radars use a very low transmission frequency from 2…3 MHz up to 20 MHz. These electromagnetic waves tend to bend or “diffract” around edges or curves, they are coupled to the conductive ocean surface forming a “ground wave”. They can bend over the horizon and will follow the curvature of the earth. The Figure 1 shows in red color an antenna pattern of an en-route radar using direct wave in Gigahertz region in comparison to an OTH–SW radar shown as the green one pattern.

Raytheon Canada and the Canadian military developed such radar, designated the HF-SWR-503. This is an oceanic surveillance system for monitoring such illegal activities as drug trafficking, smuggling, piracy, illicit fishing and illegal immigration. In addition, it may be used for tracking icebergs, environmental protection, resource protection, sovereignty monitoring and remote sensing of ocean surface currents and winds as well as assist in search and rescue operations.

It consisted of an array of monopoles 660 meters (2,165 feet) long, with the monopoles spaced at about 50 meters (164 feet), corresponding to half the wavelength of the radar's 3 MHz operating band. The array has a field of view of 120 degrees and can track targets to the limit of Canada's 370 kilometer (200 nautical miles) oceanic economic exclusion zone. It can obtain positions accurate to within hundreds of meters. Raytheon stated that a similar array could be used to track low-flying cruise missiles if it operated at a frequency of 15 to 20 MHz.

A German OTH-SW application with more civil use is the WERA radar. The WERA system is a shore based remote sensing system to monitor ocean surface currents, waves and wind direction. It uses the principle of FMCW with very slow sweep period of typically 0.3 sec. This oceanography radar can pick up back-scattered signals (Bragg effect) from ranges of up to 200 km.


Over–The–Horizon Backscattering (OTH–B)
It is also possible to build radar that has “over the horizon” range, obtained by “bouncing” or “backscattering” radio waves off the ionosphere, the ionized layer at the top of the atmosphere. It uses slightly higher frequencies (up to 50 MHz). The scheme has many similarities to OTH-SW, requiring large antenna arrays.

Even at RF frequencies, OTH-B is dodgy to do. The exact properties of the ionosphere can vary, sometimes wildly, over the course of a day, and even when it's stable it's not like a radio “mirror”, crisply reflecting radio waves back down towards the ground, instead tending to smear out and scatter pulses. Of course, along with a range of thousands of kilometers comes extremely weak returns. OTH-B requires a good deal of sophisticated radar signal processing.

Source: Radartutorial.eu


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RE: ship radar coverage - 2/11/2020 7:25:46 AM   
Parel803

 

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An other use of backscattering in radar is to see differences in returned echo's to classify. At least used in weather radars and earth penetrating radars. Ranges, I think, still detemined by there RF's, height's and curving of the earth. So also affected by objects, clutter and power to it's reflecting echo.

with regards

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