Zupt, LLC

Integrated Inertial Positioning SystemsSome facts, some editorial and some biased opinions

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Inertial Tools - What instruments are currently in daily use for Survey?

In our businessInertial navigation systems (INS) for land seismic, Vertical Reference Units (VRU’s) for DP, USBL/SBL and Swath sonar attitude/heave corrections –

Surface heading sensors – Spinning mass gyros as well as strap down Attitude Heading Reference Systems (AHRS)

In other applicationsInertial sensors - anti-lock brakes, anti skid, virtual reality headsets –Analog Devices, Crossbow, Systron, Bosch, BAe and many others

Inertial Navigation systems as (Tactical) short term positioning sensors -Northrop Grumman, Honeywell, Kearfott, BAe, Boeing, etc.

High precision (Strategic) Inertial Navigation systems for long term positioning outages - Northrop Grumman, Honeywell, Thales navigation, etc.

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Available How Long?

In discussing this exciting new technology we must also understand that these tools have been around for a while, even in the seismic and survey business:

Western Geophysical’s W-INS (“we invariably needed SHORAN”) late 1970’s

Shelltech/Itech land seismic use of INS for control (helicopter based Zupt’s) Mid/late 1970’s

Exxon/Honeywell’s DP reference systems – Riser and INS – 1979

British Oceanics/Intersub INS for manned submersible construction positioning (used in place of “the unreliable acoustic systems”) – early 1980’s

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Session Agenda

A few definitions

What is an inertial measurement unit (IMU)?

Overview of inertial sensors

Price versus performance

Where is inertial technology going?

Integrated Inertial Positioning Systems

Loosely, tightly and deeply coupled

Aiding Observations – current and future

Applications for Integrated Inertial Positioning Systems

Current and near term products

Commercial benefits of these systems

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A few definitions

An Inertial Sensor is a position, attitude or motion sensor whose reference are completely internal draft revision to IEEE Std 528

A Gyroscope is a sensor designed to illustrate the dynamics of a rotating body

In Strapdown operations the inertial frame of reference is stored in the computer as opposed to being maintained mechanically by gimbals.Coordinate transformations and sensor compensation have to be completed within the strapdown computer.

Bias - no input, but some level of output

Angle random walk - white spectrum rate detection noise leads to an angle random walk (optical and coriolis gyros)

Aiding - using external non inertial observations to minimize bias

Scale Factor- an error in the assumed scale factor in the instrument output

Schuler Oscillation/Period - 84 minutes – just think about a pendulum centered at the earth’s core and the IMU at the earth’s surface

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What does an IMU consist of?

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How does this fit together?

Measureacceleration

Compensate foraccelerometer

bias and SF

Compensatefor

gravity

IntegrateOnce-VelocityTwice-Distance

Measurerotation rates

Compensatefor

Earth’s rotation

Navigation ComputerAccelerometers

Gyros

Heading

Distance

Speed

Compensate for Gyro Bias, ARW, SF and acceleration sensitivities

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Overview of inertial sensors

Inertial sensors come in many forms and are an excuse for infinite acronym generation.

The two types of sensors within an IMU are:

Gyroscopes - rate of rotation

Accelerometers - linear acceleration

Some examples are:

Gyros Dynamically tuned, (DTG), Fiber Optic (FOG), Ring laser (RLG)

Accels Vibrating Beam (VBA), Quartz Resonating (QRA), Pendulous Mass (PMA)

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Gyro Technology

Angular Rate Sensing technology principles:

Spinning Mass - angular momentum

Vibratory/Resonator - Coriolis

Optical - Sagnac

Micro Electro Mechanical Sensor(MEMS)

primarily vibratory, some spinning mass, some optical

Micro Optical Electro Mechanical Sensor (MOEMS) another variant

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Current Gyro technology

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More Gyro details

Spinning Mass Honeywell, Northrop Grumman, RockwellPros Wide performance range 0.0001 to >100°/hr

Very low noise - (specifically gas bearing)Cons Relatively high cost

Long warm upNot well suited to strapdown applicationsSome types very fragile

Vibratory/Resonant Watson, Systron Donner, Murata, BAePros Relatively small

Minimum moving partsCons Small scale factor

Output noisyRate gyro open loopLimited performance range (getting better though)

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Pros and Cons

Optical Honeywell, Northrop Grumman, (Fibresense), Ixsea, Sagem, etc.

Pros Rapid reaction and turn on(<1s)

Ideally suited for strapdown operation

No moving parts - very rugged

Cons Performance increases with size

RLG is a high voltage device

FOG very temperature sensitive

Micro Electro Mech.Sensors (MEMS) Draper/Honeywell, JPL, BAe, AD, Bosch, etc.(only vibratory discussed)

Pros Very small

No moving parts

Very low cost

Cons Higher precision still under development

Limited performance range (only for a while)

Bias stability

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FOG block Diag.

Gyro Bias (°/hr) is usually proportional to length of fiber

The longer the fiber - the better the FOG

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RLG Block Diag.

Cervit block

Path lengthcontrol mirror

AnodeAnode

Opticalbeams

Mirror

Cathode

-Schematic of ring laser gyro. Input axis is perpendicularto the plane of page.

Detector

Dithermechanism

Gyro Bias (°/hr) is usually proportional to path length

The longer the path length - the better the RLG

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Accelerometer Technology

Linear acceleration sensing technologies:

Pendulous/Translational Mass displacement/rebalanceElectrical Restraint

Rotational Restraint

Elastic Restraint

Resonant Element FrequencyVibrating String

Vibrating Beam

Double Ended Tuning Fork

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Current Accelerometer Technology

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More accel. details

Force Rebalance Accels - Honeywell Q-Flex, Northrop Grumman A4, Kearfott Mod VII

Pros Highly Reliable - relatively low cost

Wide bandwidth

Low bias error

Cons Analog output

self heating under changing acceleration

Power consumption

Pendulous Rebalance Accels.Pros Reliable, rugged, small

Well understood error model

Pendulous Integrating Gyro Accel. (PIGA) as good as it gets

used for ICBM and general missile guidance

Cons PIGA - Cost

Resonant Element Accel. Sundstrand, Allied Signal Adkem

Pros Digital output

Low power

Cons Not good in high shock environment

Detailed calibration required

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Sensor Advances - MEMS

Wafer thick gyros - 400µm

Critical assembly process for MEMS

Assembly issues being worked on to

make a low cost, mass produced “instrument”.

Noise is the challenge I-O have low noise,

low G product – VectorSeis®

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MEMS DoD Development Program

A low cost, high G MEMS and guidance

effort is underway for a DoD joint forces

program. This effort has the following goals:

Phase 1 <75°/hr, >10,000G, <8 cubic inches

This phase should have been delivered

3 vendors selected – 2 delivered 4 months ago

Phase 2 <10 °/hr, >20,000G, <4 cubic inches

This phase should be delivered this/next year

2 vendors selected – one ready to deliver

Phase 3 <0.5 °/hr desired (<1 °/hr acceptable), >20,000G launch survivable, <2 cubic inches volume. DoD’s cost expectation for this IMU is <$1,200

Should have been delivered in 2006 – may not be needed due to deeply coupled Phase 2.

Deeply coupled L1 and L2/Lm, WAAS, SAASM GPS receiver should be incorporated as an option to Phase 2/3

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So how good is a “good” INS?

Once the sensors (just discussed) have been combined to make an Inertial Measurement Unit software has to be added to turn the raw rate (incremental rate - ? ?) and the raw acceleration (incremental velocity - ? V)data into something useful as a:

Attitude Heading Reference System (AHRS), or an

Inertial Navigation System (INS)

The performance of an INS is usually rated in terms of its position error growth rate once the INS is navigating in “free inertial” mode (no aiding).

The USAF define INS in the following manner:

INS Classification Position Error Growth Rate Heading Errors

Low > 2nm/hr >0.2°

Medium 0.5 to 2nm/hr 0.05 ° to 0.2 °

Precision <0.5nm/hr <0.05 °Following a standard ground alignment at 50 ° or lower latitude – USAF SNU84-1

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Cost versus PerformancePRICE $K

160 Department of State Controlled Technology Dept. of Commerce Controlled ?Primarily for internationallysourced IMU's only

IMAR .003º $155K 20cm RLG140

120

100 Thales Totem .001ºThales $100K 30cm RLG

T24 .003º $130K Kearfott 24cm RLGLN250 .005º? $90K 1200m? FOG

80 LN100 .003º $80K Northrop 18cm RLGPHINS .003º $80K Ixsea 1200m FOGCIMU .0035 $80K Honeywell 6" path RLG

Sigma 10 .05º SAGEM $65K 10cm RLG 60 Octans 0.01º $60K Ixsea 700m FOG (AHRS only)

40T16 .01º $100K Kearfott 18cm RLG

T90 1º $39K Tamam

20 LN200 1º $22K Northrop 200m FOGBOEING 3º $20K MEMS

0.002 0.015 0.15 1.5 15 BIAS STAB º/hr

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Where is this technology going?

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Maturity of technology

Draper Laboratory’s view

on the state of current

development.

The suggestion is that most

technologies are now mature

except for MEMS gyros.

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Export Control

The fastest way to go to jail (without passing go) will be to flaunt the export controls associated with this technology.

The International Traffic in Arms Regulations (ITAR) and the Arms Export Control Act (AECA) are the governing law that is overseen through the Directorate of Defense Trade Controls (DDTC www.pmdtc.org) within the U.S. Department of State (remember Colin Powell).

Simply put (to me by the DDTC) “if you screw up, it will be you, not the company, that goes to jail”.

DDTC is responsible for all licensing issues if the commodity is controlled by State.

To get a commodity under the more understanding Dept. of Commerce control a “Commodity Jurisdiction” has to be filed with the D.o.State.

Most US manufactured and “high end” international IMU’s will fall under the control of the DDTC

Do not listen to the vendors when they say don’t worry about this –talk to your own export attorney and get their advice.

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What type of sensor do you need to buy/integrate?

• As can be seen from the previous charts IMU’s are available in many flavors. The one underlying suggestion I would make is to:

Only buy the sensor with the performance you really need

Do not over specify the performance requirements of your sensor or it will cost significantly more than it should.

OR ?

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Free Inertial Drift$100K buys apx. 20 meters for 20 minutes free inertial. This level of inertial

performance is not needed if the IMU errors can be bounded with some form

of external aiding – hence the need for Integrated Inertial Positioning Systems.

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System Integration – Coupling?

A very basic “Loosely Coupled” system –

the INS and aiding system provide

position and velocity into the Kalman filter.Example GPS/INS

GPS would provide Position and Velocity

INS would provide position and

velocity

“Tightly Coupled” – the IMU and aiding

system provide raw observations that

are modeled within the Kalman filter.Example GPS/INS

GPS would provide code and phase observations,

the IMU provides rate and acceleration observations.

INS

KalmanFilter

Aiding NavSystems

IMU

KalmanFilter

Aiding NavSystems

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Deeply Coupled

IMU

KalmanFilter

Aiding NavSystems

“Deeply Coupled” – the IMU and aiding

system provide raw observations that

are modeled within the Kalman. The

solution provides feedback into both

the IMU and the aiding observations.

Example GPS/INS

GPS would provide code and phase observations,

the IMU provides rate and acceleration observations.

The GPS receiver is controlled to “window” onto expected arrivals of SV data. Significantly improves the

signal to noise performance of the GPS system. Currently in use for anti jamming and blocking of GPS

signals in defense applications.

Just imagine what a deeply coupled acoustic line of position/INS solution would do for ROV

positioning? Improving the SNR of the system!

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Why spend effort on better coupling?

Assuming life was good and GPS was very visible –a loosely coupled solution will work well – why would we need such a system (GPS/INS)? High update rate position with precision attitude information (LIDAR, Photogrammetry etc.)

Now we start to require GPS observations in a crowded urban area (road survey)– the GPS solution fails, no position or velocity – my loosely coupled GPS/INS solution starts to fail.

The same is true for land survey under canopy. With some visibility, a loosely coupled system should provide a solution as long as the GPS system provides a position and velocity.

Once the canopy thickens such that only occasionally data is available from some SV’s then a tightly or deeply coupled solution will provide a valid solution much longer.

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In Offshore ApplicationsROV Long Baseline construction survey tasks

To go to work a LBL array has to be deployed and calibrated – takes time and equipment, usually on the critical path.

The ROV then positions itself within this array to complete the subsea construction tasks. The conventional LBL solution could be integrated with an IMU to get a higher update rate and precision attitude info. This may have some value. But if if this integration is taken one step further we will be able to offer significant savings to offshore operations.

What if we could reduce the number of beacons in the array and position the ROV with just a tightly coupled INS/Line of Position (with respect to a seabed mounted transponder) solution? Deeply coupled would be even better as we could extend our acoustic range as we improve our SNR due to driving the acoustic transceiver.

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Aiding Observations – what is available?

Many aiding observations are used to bound the error growth of IMU’s. A few of the normal and not so normal observations are listed below – some from air, land and marine (I am sure I have left many out):Conventional:

GPSZero Velocity Update - ZuptDoppler velocity sensors/logs (airborne radar and underwater acoustic) Altimeters (RF and acoustic)Depth sensorsPedometersDistance Measuring IndicatorsRange/Range systems (RF and acoustics)Half Gauge (Rail tracking indicator)Terrain matching – matching to existing terrain data

Not so conventional:Vision – relative position and velocity from CCD or SIT images (already working)Stripe laser illuminated imagery – very high definition=resolution observations (near to working)Swath Sonar - relative position/velocity from image processing of sonar data (working today)Terrain Mapping – establishing the environment around the system and noting changes as they occur (prototypes working at MIT allowing navigation around halls

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Commercial Benefits

Let’s take a look at just a few examples of integrated solutions to try and understand why these systems will make inroads into our business over the next few months/years:

Marine Construction

Dynamic Positioning

Land Seismic Stake Out under Canopy

A list of “No brainer” uses

As you will see all of these applications of an integrated solution are affordable through real operational savings. The benefits are not just better data, higher update rate, more reliable solutions –

The incentives are real dollar savings through the life of projects

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Marine Construction

What are the issues for the marine construction survey community?

Boat time, Boat time, Boat timeAny operational gain that can be made to reduce the amount of vessel/spread time consumed specifically for the survey aspects of marine construction tasks will go straight into savings for the end customer – do these customers really care?

The marine construction survey community need to be able to reduce vessel/spread time while completing tasks similar to the following:

Metrology – providing repeatable, reliable positioning data while consuming minimal ROV/spread time. A local, relative positioning problem well suited to an aided inertial solution.

Local field development positioning - 300mx300m subsea infrastructure relative installation – significantly reduce the operational time currently consumed to deploy and calibrate large LBL arrays, reduce the LBL beacon count significantly.

Wide area deepwater absolute positioning – 3,000mx 3,000m field wide control with significantly reduced acoustic observation sets. Vessel/ROV spread consumption reduced due to less hardware deployed on the seabed. Such an application would be deepwater permanent suction mooring installations.

Deepwater pipeline “as built” survey – improve the survey deliverable from USBL systems by aiding with an inertial observation set – no need for LBL.

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Marine Construction Example

Using an example of a project that has multiple frame sets including an array installation and calibration at 4 locations:

Each location: 5 Far field transponders, 6 Near field transponders2.8 boat/ROV spread days per location for deployment/calibration, 4 locations$65K/day complete spread rate - 4(2.8x65) = $728K

If proven aided inertial tools are availableEach location: 2 near filed transponders (absolute array orientation taken care of with good IMU), 1.3 boat/ROV spread days per location, 4 locations$65K/day complete spread rate 4(1.3x65) = $338K

A very conservative estimate of savings = $390K on a single job – this savings would nearly pay for the system development

OR

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The DP – IMU/ERA Case

Riser Operating inNon Bi-Stable Mode

Riser ModelIncluding:Riser Angle TensionMud WeightSlip JointPosition

IMU

Patented in 1979, not used since – Class 2 and 3 DP

Requires “3 independent ref systems from 2 different

Operating principles”.

Today in deep water we only have two systems to

choose from - GPS and Acoustics. The numbers work for

this solution as well.

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The $ Benefit for DP Operators

Graceful disconnect/ shut down of operations $1,000,000/incident

Short term DGPS outage $Operator penalty or disconnect

Slow down acoustic update

Assist the “Multi-user” problem $To work or not, penalty

Extend battery Life $45,000/year

Additional reference sensor $100, 000 or penalty saving

DP model “smoothing”

Less fuel consumption $Does the client care?

Less “wear and tear” $1,000,000/repair incident

(Seal failure * recent example)

Heading, pitch, roll, heave $40,000 + $50,000

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Land Seismic Stake Out Under Canopy

This is one of the sectors where aided inertial systems have been trying to find a home for the past several years. What are the issues for the land seismic community?

When seismic acquisition moves into wooded or forested areas the canopy starts to impact the reception of the direct GPS signals as well as the radio link for RTK.

The primary system will consist of a very good IMU bounding it’s error through the use of Zupt’s. Occasional RTK GPS may be available, but in many cases the days survey is completed with just the IMU and Zupt’s. These systems deliver sub 1m post processed accuracy with good initial calibrations and good closing RTK calibrations.

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Land Seismic Stake Out Under Canopy

Survey time to stake out under canopy requires cutting of the canopy to allow for conventional optical survey tools to be used. Using backpack based inertial instruments significantly reduces the amount of time taken to survey locations.

Conventional cutting and surveying will achieve perhaps a mile a day or less under canopy

Inertial based systems allow between 3 to 4 miles per day (4 times conventional production), and in some instances up to 8 miles per day.

Cost per mile $1,000/mile, line miles on an average (no such thing) 3D land survey will be (a line every .25 miles – 10x10 mile survey) 400 line miles.

Other very significant issues are:

Environmental issues – minimal cutting (low impact seismic) is being specified more often

Safety issues – significant issues associated with HS&E

OR

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Some more examples of “No Brainers”

Some of the current issues facing the survey and positioning community that will benefit from Integrated Inertial Positioning Systems:

EM or 4C/D seabed station installationsLarge numbers of nodes that require precise installation in deep water. Currently primary options are very large LBL arrays as USBL cannot provide the accuracy required. A combined DVL, LOP, Depth and IMU solution will subtracts days from the deployment and calibration of such systems

Metrology/Spool piece measurementSome valiant efforts (CDL – Subsea7) to use systems. The introduction of a proven and fullyaccepted capability would reduce many hours from each measurement set. Just taking a look at some of the west African field development should pay for the development and proving of such a solution.

Acoustic PollutionSlow down update rates, make acoustic bandwidth available through the use of less acoustic channels, DP, construction, ROV tracking and seafloor positioning will all benefit significantly with even a loosely coupled IMU in the loop. No need for massive, commercially confusing, pseudo ranging “Seabed GPS” systems.