Survey and GPS Denial

Discussion in 'Gunners' started by Proximo, Sep 21, 2006.

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  1. Exam Question: What options exist for the Gunners to provide accurate survey under conditions of GPS denial?

    Most modern systems on the battlefield use some form of positioning system, and most of these are reliant on GPS, possibled coupled to an INS of some description. But what do we do when GPS is denied? Revert to thumbprint and prismatic compass? Hope to find nicely marked out trig points to park over?

    Serious question - any genuinely serious answers and solutions gratefully received.

    Many thanks.
  2. I once asked a Sound Ranger how they surveyed in their equipment (HALO, Bos 96/97).

    IIRC correctly, it was using theodolytes from a known starting grid out to the location, then dog-legging back to the start point as an error check.

    What I found funny, was the known starting grid was acheived using GPS. The troop then spent several hours doing complicated things with orange boxes on top of 3 sticks to get to the location.

    Why not just use the fecking GPS at the final location, and save several hours of arithmetic?

    When asked how it was possible to find a 13 Fig Grid without GPS, I was looked at as if I was completely stupid ( I am stupid, but I thought the question was relevant).

    As an aside, can someone explain how a North Seeking Gyro points to North?
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  3. As far as I can dimly recall, it's to with the spinning of the gyroscope and how it is affected by the Earth's gravity and rotation. As the 'disc' spins, it naturally comes under the influence of these 2 forces and therefore lines up with the 'True North' along the Earth's meridian.

    I may have it slightly wrong, however... :D
  4. Ive had a bash at this check your PM's mate.........
  5. What? Like trees you mean?
  6. The more accurate the survey, the more accurate the location, I remember years ago we trailled GPS to survey our mic base in (the GSR not ASP system) and the locations were pony. Now I can't comment on the current method of ASP but when I did HALO training we used GPS to stick out the clusters as our only means of survey and we got fairly good locations off it.

    You could argue the Bosnia scenario in 2 ways


    a. As the mic clusters were in "permenant" locations and there were qualified surveyors in the troop it makes sense to get the best co-ord posisible


    b. The quiche eaters just love doing diamond traverses

    How it all works now I am unsure, but I thought I heard that the Sound Rangers no longer had a Survey troop, they were moved to Q HQ Bty
  7. There are 3 types of GPS denial: "jamming" is likely but easy to spot; "spoofing" is also relatively easy to spot but is more unlikely; and "meaconing", which is difficult to spot but (thankfully) unlikely:

    Very unlikely - "Spoofing" is the sending of a "GPS-type" signal. This is unlikely and most military standard GPS can spot this bogus signal as the standard of encryption of the GPS signal is high (and due to increase).

    Unlikely - "Meaconing" (no I did not make this term up!) is the re-broadcast of genuine GPS signals (usually at a stronger strength than the satelite signal). Unless you can monitor the GPS signal strength, then you will not be able to spot this rebroadcast. So what? Bad news - it will give you an incorrect solution to the time/distance equations that produce your grid, it can skew your position substantially. Good news - your GPS will usually take signals from a number of satelites and may have the ability to discount faulty signals.

    Likely - Jamming: If you GPS does not receive a signal then you can guess that the GPS frequency is being jammed. This relies on a line-of-sight jammer - so if you shield your GPS from this then as the satelites are above you head, you should get a signal.

    So what? A jammer the size of a coke can, made at a cost of $200 will jam 1km square. Any university physics student should be able to make one. The others are made in either a technologically advanced country - or one with money to buy it from the Russians/Chinese. We do have boffins who are looking to ways of getting round these difficulties, especially in an era when the US are talking about "navwar" when we will need to know what is going on.

    Conclusion - while the GPS system is robust, we should never have lost the traditional svy capability (the bean counters will say that it is too expensive to teach). It’s lost now and we will never get it back.


    PS - before I get a slagging, I am not a techie geek - I had to research this at Schriv.
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  8. Drop_Short - any chance I can get a peek at your Shriv work?

    I'll PM my civvy email to you.

    With regard to 'never getting it back', I agree that lack of money and short-sightedness is preventing instruction on traditional survey methods. I can remember when AS90 rocked up and the cry was 'We mustn't rely solely on GPS - we must have INS coupled to update points.'

    Well, what on earth happened? I'll tell you. It was determined by HQ DRA that maintaining Directors was simply too expensive, so in a stroke we went from a high degree of technical competence with Survey to a GPO's thumbprint on a map.

    It doesn't need to be this way. We have 60 electronic total stations on shelves in RSA, 48 sets of LAGERS and god knows what else - all paid for and with a fraction of the through-life costs of Director.

    It's utterly astonishing that this has been allowed to happen.
  9. Darth,
    I wholeheartedly agree. The level of survey knowledge has declined rapidly over the past five years. I'm not even sure who (in the guns world) is actually taught survey to a useful standard.

    That saying, there is the age old argument that errors in survey could be shot out. But what happens to commonality????
  11. It's a long time since I had to do with this, but here goes

    The process is called gyrocompassing and depends on having a very accurate gyro whose spin axis is governed to the local horizontal plane, possibly controlled by simple gravity sensors such as mercury tilt switches. This takes out the vertical, or 'topple' element of apparent wander caused by the earth's rotation, but leaves the gyro free to 'drift' in the horizontal plane as the earth's rotation takes effect.

    The very simplest explanation of what happens then is to say that any gyro may be considered to be a device that detects rotation and it is only when the spin axis of our gyro points to local true north that there is no horizontal rotation input because of earth rate. To expand upon this we might say that if it is displaced from true north, the earth rate input will cause it to precess until its axis points to true north again.

    The way this works in practice depends on the gyro mounting: there is an outer gimbal bearing, free to rotate in the horizontal plane, that supports the gyro/inner gimbal system. At this bearing, if the axis does not point to true north, earth rate drift produces a movement between the inner part (say), which is attached to the gyro/inner gimbal assembly, and the outer part, which is fixed to the earth. The one rotates relative to the other. This rotation is detected electrically, and the resulting error signal (probably a voltage, but ask a clever chap about that) is used as the input to a feedback control loop containing a servo motor that drives the gyro assembly back in the opposite direction. This effect eventually causes the gyro spin axis to point to local true north, less any hang-off error in the feedback loop.

    Unfortunately, to explain any more convincingly, you really need a three dimensional model to show how the gyro drifts and the correction is generated and applied.
  12. As much as I hate to disagree with Darth (damn fine chap that he is) I must do so on the subject of Survey. I taught conventional survey as a SMIG for 2 years and always knew in my heart of hearts that it was not an act of war.

    All those rattles and flags to produce a grid that to be frank was either complete bollocks or much more accurate than you needed.

    In the old days guns needed to be fixed very accurately because we were worried about the orientation (an inaccurate grid made any errors from the director much worse) Now their is no need to fix a gun to anything more than 10 - 15m as the orientation will always be true to 1 Mil (provided by the INS not the GPS)

    The current UK standard for Bravo line is much higher than the NATO STANAG and arguably has never ever been achieved by any UK Gun Bty as it calls for orientation to decimals of a mil which the gun sights physically cannot do!

    GPS is very definitely the way ahead it’s cheap, accurate enough and easy to use, (ease of use is essential; as we already have a 9 week Command systems cse and cannot afford either financially or in time away from busy units for it to be longer).

    Their was a move mooted by the author of Survey in the Unit (and my old boss another top bloke!) to put the INU from APS into a veh fit and load it into the SIGS/SVY land rover. This system which was to called WINS (Wheeled vehicle mounted Inertial Navigation System) would then be use ala PADs to provide fix in the event of GPS denial. I don’t think this has been funded so currently when the systems go down you fix the gun by map spot and put it on by compass (incidentally we fired light gun all day once in the reversionary mode for an OP cse who didn’t notice because we didn’t tell them!!)
  13. Wittman

    I though the Gun Tower for the Light Gun had a repeater for the LINAPS system in the cab? If this is correct, isn't this a version of what your old boss was recommending?
  14. We still have most of 'our' Total Stations in the stores (45 -50 TC/T 1100 from Div Svy 5 Regt RA) it only costs £300 to have them calibrated at Leica therefore we dont need to buy any new kit. ASP are using these over the Director at the moment, to save time and gain extra accuracy.

    Within the STA disciplines we will still need an optical instrument, therefore it would give us a very limited 'back up' if trained, nowhere near as the 50 odd Surveyors from the axed Div Svy Tp.

    We still have ppDGPS (LAGERS) sitting on the shelves which would enable a large number of SCP to be put out before we are jammed.

    I don't think we take NAVWAR as seriously as we should, and also the STA community has a greater need for Svy than the CS world, therefore needs addressing.
  15. And when the yanks turn 'off' gps, then what?

    Pads (old i know) is not man - portable. Map, compass, log tables and a knowledge of stars and sun will win evrey time :D

    Remember, our American cousins had to appologise for saying we had wrong heighted Everest :lol:
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