Search Coverage

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Air OperationsBranch Director Course

• Navigation Fundamentals Understanding GPS for
  Sortie Planning

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Goals for understanding

• Prepare mission staff to be able to plan and
  brief missions that can be executed efficiently
  and conveniently with our equipment
• Navigation fundamentals
• Capabilities and limitations of GPS
• Capabilities of Apollo GX55 GPS units in
  Minnesota Wing aircraft
• What information is needed to program the GPS
  unit for search patterns
• What can and cannot be programmed in the GX55
• What can be improvised
• Learn about the gotchas using GPS

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PART 1Navigation fundamentals

• Latitude and longitude
• Describing directions

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Latitude

• Parallels
• Measure How Far North or South of Equator
• Zero Degrees is Equator
• 90 Degrees North is the North Pole
• 90 Degrees South is the South Pole

North Latitudes
Equator
South Latitudes
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Longitude
East Longitude
West Longitude
Prime Meridian
Longitude

• Half Great Circles Intersecting at the Poles
• Measure How Far East or West of England
• Zero Degrees is Prime Meridian (England)
• Numbers between 0 and 180 are either East or West
  Longitude
• 180 Degrees is opposite side of globe from
  England
• near international date line in Pacific Ocean

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Latitude and Longitude

• Latitude is Based on Earths motion
• Axis of rotation defines poles and Equator
• Longitude is Arbitrary
• Greenwich, England was chosen for prime
  meridian.

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Wheres Minnesota?

• Twin Cities
• Northern Minneapolis is at 45 Degrees North (half
  way between the Equator and North Pole!)
• 93 Degrees West is roughly the Eastern edge of
  St. Paul.
• The Northwest corner of the state
• Exactly 49 Degrees North
• Roughly 97 Degrees West

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How Big is One Degree?

• Degrees of Latitude are always the same distance
  apart, about 60 Nautical Miles
• Degrees of longitude vary in distance near the
  poles the lengths are quite small.
• In Minnesota, a degree of longitude is about 40
  to 44 Nautical Miles across

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Dividing Degrees into Smaller Units

• A Minute 1/60th of a Degree
• roughly a mile in size
• Minutes are usually broken down into tenths of
  minutes
• Alternatively, a Second is 1/60th of a minute

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Expressing Latitude and Longitude in Degrees and
Minutes

• Small high circle after number denotes degrees
• Apostrophe after number denotes minutes
• Example Minneapolis Flying Cloud Airport
• 44o 49.63 N 93o 27.43 Wread as44 degrees
  49.63 minutes North 93 degrees 27.43 minutes West

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Expressing Latitude and Longitude in Degrees,
Minutes, and Seconds

• A double-quote after a number denotes seconds
• Example Minneapolis Flying Cloud Airport
• 44o 49 37.8 N 93o 27 25.8 Wread as44
  degrees 49 minutes 37.8 seconds North 93 degrees
  27 minutes 25.8 seconds West

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Determining Coordinates from a Chart
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Expressing Direction The Compass Rose
360
330
30
N
60
300
W
E
90
270
120
240
Directions are expressed as a number from 001 to
360
S
210
150
180
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Magnetic Variation

• The Magnetic North Pole is located in Canada, not
  at the True North Pole.
• The difference in direction between the two poles
  is measured and referred to as magnetic variation

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Magnetic Variation in the US
-15º
20º
15º
-10º
-5º
0º
10º
5º
Easterly Variation
Westerly Variation
Note These lines move over the years because
the magnetic north pole is in motion
Agonic Line
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PART 2 - GPS

• Overview of GPS for SAR
• Motivation
• Potential uses for SAR
• How it works
• Accuracy
• Limitations and Gotchas
• Terminology
• Describing search patterns for the GX-55
• Improvising

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Motivation

• GPS is a powerful tool for search and rescue
• Allows very precise search patterns
• Makes manageable what would otherwise be very
  difficult patterns
• Expanding square at any angle
• Creeping line along a course
• Offset route searches
• Grid searches over indistinct terrain
• GPS should be our primary tool for Search and
  Rescue navigation
• GPS is of course also very handy for general
  navigation

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Potential uses of GPS for Air and Ground SAR

• Getting to/from a search area
• Going to a location designated on a map
• Going to a site identified by another SRU
• A ground team going to a site previously
  identified by an aircraft
• Navigation while conducting a search pattern
• Clue logging (and re-finding)

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GPS for SAR Potential advantages

• More flexible search area partitioning
• More accurate logging
• More accurate search lines
• Easier and more accurate communication of
  location information

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Other GPS SAR Uses

• Electronic distress signals
• PLBs Personal locator beacons
• ELTs Emergency locator transmitters
• EPIRBs Emergency Position Indicating Radio
  Beacons
• New 406 MHz digital beacons sometimes transmit
  GPS coordinates
• GPS then becomes a tool for both the rescuer and
  the rescued

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How it Works The Basics

• Spaced-based system (unlike Loran or VOR)
• Constellation of 24 satellites in six orbital
  planes
• 21 active satellites plus 3 operating spares
• In High orbit of about 12,000 miles
• Each circles the Earth about every 12 hours

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How it Works The Basics

• GPS satellites transmit information
• Pseudo-random code with time information
• Satellite orbital position data
• Almanac data
• Ephemeris data
• Updated atmospheric models
• GPS receiver uses this data to figure out what
  time it is and what time the signals were sent

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How it Works The Basics

• GPS receiver measures distance to satellites by
  determining the amount of time that the radio
  signal takes to travel from each satellite
• Each distance measurement effectively defines a
  sphere around a satellite
• Multiple satellites must be used to determine a
  position
• Given two satellites, two sphere intersect to
  determine a circle
• Given three satellites, a sphere and a circle
  intersect to determine two points
• A fourth satellite can determine a positive 3D
  position

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Accuracy

• A complex question
• DOD has a 66 page document describing the
  performance of GPS Standard Positioning Service
  (SPS)
• The short story
• Garmin states that their GPS receivers are
  accurate to within 15 meters on average
• Typically about 6 to 12 Meters accuracy can be
  seen

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Accuracy

• Accuracy and reliability is actually a complex
  subject. There are many factors that can impact
  system.
• Receiver errors
• Atmospheric (ionosphere) errors
• Solar activity (sun spots and solar storms)
• Location of receiver
• (some parts of the Globe get better coverage than
  others)
• Orbital errors (inaccuracies in the reported
  orbital position)
• Poor satellite geometry (satellites lined up or
  bunched up)
• Limited number of satellites in view
• Satellite malfunctions (or satellites taken out
  of service)
• Multi-path errors (radio signal reflections)
• Results vary hour by hour, day by day

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Accuracy

• There is a substantial difference between typical
  accuracy and worst-case accuracy
• Described as a statistic x had an error of y
  meters or less
• Typical 95 horizontal error results for a
  typical day

Errors worse than 30 meters are possible given
the potential for various atmospheric conditions
and receiver faults and the possibility that
satellites can be taken out of service
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Accuracy andSelective Availability

• Past feature of GPS SPS that purposefully
  degraded accuracy of position determination for
  non US-military use
• Civilian accuracy was typically about 100 meters
  under Selective Availability
• SA was discontinued May 1, 2000
• Has not been used since
• It's been replaced by selective deniability,
  which allows the US military to geographically
  designate areas in which to degrade GPS quality.

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Comparing Accuracy with and without SA A
sample

• The plots show that SA causes 95 of the points
  to fall within a radius of 60.7 yards. Without
  SA, 95 of the points fall within a radius of 7.9
  yards.

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Comparing Accuracy with and without SA Recap

• Before, with 100 meter typical accuracy allowed
  you to identify what stadium you were in
• Now with 6-12 meter typical accuracy, you can
  tell about which yard line you are on

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Accuracy WAAS

• Wide-Area Augmentation System
• Designed specifically for aviation
• Commissioned by FAA in 2003
• Uses ground stations and satellites
• 25 ground reference stations cover the entire US
  and parts of Canada and Mexico
• Augments GPS Standard Positioning Service
• Provides better integrity and accuracy
• Typical accuracy of 3-5 meters horizontal, 3-7
  meters vertical
• Can be used for precision approaches

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Accuracy WAAS

• How it works
• Two master stations, located on either coast,
  collect data from the 25 reference stations and
  create a GPS correction message.
• This correction accounts for GPS satellite orbit
  and clock drift plus signal delays caused by the
  atmosphere and ionosphere.
• The corrected differential message is then
  broadcast through one of two geostationary
  satellites, and is then received by a
  WAAS-capable GPS receiver.

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Accuracy Differential GPS

• Provides high accuracy for a small area
• Uses a local ground station transmitter
• Accuracy can be better than one inch

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Limitations

• Requires good line-of-sight to satellites
• May occasionally have difficulty using GPS in
  vehicles
• Generally unusable inside a building (or cave)

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Other concerns

• GPS can be subject to accidental and intentional
  interference
• Easily jammed using strategically placed
  low-power transmitters
• WAAS is also at risk
• Selective Availability (SA) or SCATANA could be
  instituted during a national emergency (but this
  is unlikely)
• Current plan calls for possible use of Selective
  Denial where GPS is degraded or denied to
  specific geographic areas

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Gotchas

• True vs. Magnetic directions (a configuration
  option in some units)
• The Apollo GX 55 will always use magnetic
  directions
• Batteries!
• The need for training and practice
• Expressing coordinates
• Seconds vs. Decimal Minutes

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Terminology

• Describing places
• Describing directions

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Terminology Waypoint

• A specific named location either defined by the
  user or defined in the instruments database
• Waypoints sometimes come in flavors
• User defined waypoints
• Built-in database waypoints (example an airport)

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TerminologyDefining Different Directions

• Desired Track / Course
• Bearing
• Track
• Heading
• In general, you should take note whether your
  GPS is giving you directions as True or Magnetic
  directions
• The GX-55 always gives Magnetic directions

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Describing LocationsA Choice to Understand

• We describe latitude and longitude normally using
  degrees and minutes
• When dealing with fractions of minutes there is,
  however, a choice
• There are essentially two options
• One can use seconds (of which there are 60 in
  one minute)
• One can use decimal-minutes (i.e. tenths and
  hundredths of a minute)
• Many GPS units can be configured to display one
  way or the other

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Describing LocationsYet another option

• Sometimes, latitude and longitude are expressed
  in degrees only.
• Thus the following are equivalent expressions of
  longitude
• 93o 20 00
• 93.33333o

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Describing LocationsCAP Standard Method

• The standard we will use in CAP is degrees and
  decimal minutes
• Example
• 45 degrees 35.4 minutes North
• 93 degrees 42.2 minutes West
• This is the standard way the Air Force provides
  coordinates to us for search and rescue
• This is also the way our GX-55 normally displays
  position information
• In CAP we will not usually use seconds unless
  working with another agency that wishes to do so.

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Describing LocationsCommunicating with Others

• The seconds vs. decimal minutes question is a big
  source of confusion even within single
  organizations
• Some people erroneously say seconds when they
  mean hundredths of a minute
• Some people say point or decimal when they
  should have said minutes and seconds
• Take nothing for granted when getting information
• Be accurate and clear when giving information
• Especially when working with other-agencies,
  triple-check all coordinates to make sure were
  all speaking the same language
• Some organizations normally uses
  Degrees-Minutes-Seconds as their standard way of
  describing positions, but they will use the word
  decimal or point to separate the three parts
  of the coordinate

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Describing LocationsYet Another Approach to be
Aware of

• Some GPS units also offer the option to display
  position information using Universal Transverse
  Mercator (UTM)
• An alternative to using degrees and minutes
• Beyond the scope of this course

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GX-55 Search patterns

• Describing the patterns
• Parallel Line (Grid)
• Creeping Line
• Expanding Square
• Route and offset route

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Parallel Line Search Patterna.k.a. Grid Search

• US Grids are areas 15 minute to a side,
  serially numbered for each sectional chart (MSP
  means Twin Cities sectional)
• 7.5 minute quarter grids are named A, B, C, and D
  in reading order, left to right, top to bottom

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Parallel Line Search Patterna.k.a. Grid Search

• The GPS unit labels the four corners (and also
  four search pattern entry points) 1, 2, 3, and 4
  clockwise starting in northwest.

1
2
MSP 413 A
4
3
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Describing a Parallel Line Pattern

• Grid identifier and starting waypoint (i.e.
  corner of quarter-grid)
• Track spacing
• Direction of tracks either E/W or N/S
• Note Search area for a parallel line pattern in
  the GX55 is always a quarter-grid

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Parallel Line Pattern Example

• Quarter Grid MSP 413A1
• Northwest corner of grid MSP 413A
• Track spacing 1 NM
• Tracks running east to west

MSP 413 A
Track spacing
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Creeping Line Search Pattern

• Shaped much like a parallel line pattern, but
  with legs aligned perpendicular to a route
  (rather than by ordinal directions)
• Descriptive parts
• Starting point (any waypoint)
• Direction
• Starting left or right side
• Track spacing
• Leg length
• Number of legs

Direction
Track spacing
Leg length
Starting Waypoint
Starting on left side
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Expanding Square

• Descriptive parts
• Starting waypoint (at center of pattern)
• Initial direction
• Track spacing
• Number of legs

3s
s
s
2s
s
2s
3s
Initial Direction
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Expanding Square

• Descriptive parts
• Starting waypoint (at center of pattern)
• Initial direction
• Track spacing
• Number of legs

3s
s
s
2s
s
2s
3s
Initial Direction
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Offset Track Line Searcha.k.a. Route Search

• For a returning route search, 2 passes are made,
  each ½ track spacing offset from base course
• A non-returning route search will have a leg on
  the base course

TO Waypoint
Base Course
FROM Waypoint
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Offset Track Line Searcha.k.a. Route Search

• For the purpose of using the GPS, we can program
  only one leg at a time
• A route leg will either be
• On the course line (in which case a simple flight
  plan will suffice)
• Offset from the course line
• Described as a distance offset and a direction
  offset (either right or left of course)

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Improvising

• As a last resort, any GPS can display running
  latitude and longitude
• The crew fly the pattern watching the numbers
• This can be used to guide an arbitrary grid
  search
• Example usage we need to fly a grid which has
  non-standard boundaries
• This generally requires additional preflight
  preparation (to predetermine the lines of
  latitude and longitude)