Transcript Search Coverage - Minnesota Wing Civil Air Patrol

Air Operations
Branch Director Course
U.S. AIR FORCE
AUXILIARY
Navigation
Fundamentals
& Understanding
GPS for Sortie
Planning
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
PART 1
Navigation fundamentals
Latitude and longitude
Describing directions
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
West Longitude
Prime Meridian
East Longitude
Longitude
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
Latitude and Longitude
• Latitude is Based
on Earth’s motion
• Axis of rotation
defines poles
and Equator
• Longitude is
Arbitrary
• Greenwich,
England was
chosen for ‘prime
meridian’.
Where’s 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
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
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
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’ W
read as…
44 degrees 49.63 minutes North
93 degrees 27.43 minutes West
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” W
read as…
44 degrees 49 minutes 37.8 seconds North
93 degrees 27 minutes 25.8 seconds West
Determining Coordinates from a
Chart
Expressing Direction:
The Compass Rose
360
330
30
N
300
270
60
W
E
240
90
120
210
S
180
150
Directions are
expressed as a
number from 001
to 360
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
Magnetic Variation in the
US
-15º
-10º
-5º
0º
+15º
+5º +10º
+20º
Easterly Variation
Westerly Variation
Note: These lines move over the
years because the magnetic north
pole is in motion
Agonic Line
PART 2 - GPS
Overview of GPS for SAR
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Motivation
Potential uses for SAR
How it works
Accuracy
Limitations and Gotchas
Terminology
Describing search patterns for the GX-55
Improvising
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
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)
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
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
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
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
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
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
Accuracy
Accuracy and reliability is actually a complex
subject. There are many factors that can
impact system.
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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)
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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
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:
Global average
7.8 – 8.3 meters
Average for worst site
(on globe)
19.2-19.7 meters
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
Accuracy and
“Selective 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.
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.
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
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
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 WAAScapable GPS receiver.
Accuracy – Differential GPS
Provides high accuracy for a small area
Uses a local ground station transmitter
Accuracy can be better than one inch
Limitations
Requires good line-of-sight to satellites
– May occasionally have difficulty using GPS in
vehicles
– Generally unusable inside a building (or cave)
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
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
Terminology
Describing places
Describing directions
Terminology: Waypoint
A specific named location either defined
by the user or defined in the instrument’s
database
Waypoints sometimes come in flavors:
– User defined waypoints
– Built-in database waypoints (example: an
airport)
Terminology:
Defining 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
Describing Locations
A 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:
1. One can use seconds
(of which there are 60 in one minute)
2. 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
Describing Locations
Yet another option
Sometimes, latitude and longitude are
expressed in degrees only.
Thus the following are equivalent
expressions of longitude:
– 93o 20’ 00”
– 93.33333o
Describing Locations
CAP 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.
Describing Locations:
Communicating 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, triplecheck all coordinates to make sure we’re 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
Describing Locations
Yet 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
GX-55 Search patterns
Describing the patterns
– Parallel Line (Grid)
– Creeping Line
– Expanding Square
– Route and offset route
Parallel Line Search Pattern
a.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
46o 00’ N
B
A
414
D
C
45o 45’
MSP
413 A
445
446
45o 30’ N
93o 45’
94o 00’ W
93o 30’ W
Parallel Line Search Pattern
a.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
46o 00’ N
MSP
413 A
4
94o 00’ W
3
45o 52.5’ N
93o 52.5’ W
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
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
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
Starting
Waypoint
Starting on
left side
Expanding Square
Descriptive parts
– Starting waypoint (at
center of pattern)
– Initial direction
– Track spacing
– Number of legs
3s
s
s
2s
s
3s
2s
Initial
Direction
Expanding Square
Descriptive parts
– Starting waypoint (at
center of pattern)
– Initial direction
– Track spacing
– Number of legs
3s
s
s
2s
s
3s
2s
Initial
Direction
Offset Track Line Search
a.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
FROM
Waypoint
Offset Track Line Search
a.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)
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)