7 SEARCH TECHNIQUES REFRESHER
ver 2013.07
Overview......................................................................................................................................
1
Search Technique Acronyms.....................................................................................................
2
Lost Person Behaviour.................................................................................................................
3
The Missing Person Matrix............................................................................................................
3
Passive Searching.........................................................................................................................
3
The 300m Circle............................................................................................................................
4
Sound and Light............................................................................................................................
4
Types of Sound...................................................................................................
4
Spacing...............................................................................................................
4
Use with other Search Methods..........................................................................
4
Sound Line....................................................................................................................................
5
Sound Sweep................................................................................................................................
5
Sound Light Line and Sound Light Sweep....................................................................................
6
Purposeful Wandering..................................................................................................................
6
Searcher Spacing...............................................................................................
6
Critical separation..............................................................................................
6
Coverage...........................................................................................................
7
Methods.............................................................................................................
7
Probability of Detection...............................................................................................................
8
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Overview
The reality is that in a search operation the people in the field are the people on the spot and are
therefore in the best position to take into account all the variables, including the changing weather,
ambient light, terrain, vegetation, as well the likely behaviour of the lost subject. This module will
explore the ‘best practice’ of a variety of search methods and key search concepts that will cover
most scenarios likely to be encountered. We will explore the techniques and methodologies but
ultimately it will be up to you to use your intelligence, experience, training, and judgement in the
way you go about searching as only you can take into account all the factors on the day.
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Search Technique Acronyms
LKP
PLS
DOT
POD
DP
LPB
ROC%
This is the Last Known Point
The LKP is based on evidence of some kind. This may be the subject’s car at the road
end, a track or hut logbook entry, likely sign or footprints, found clothing/equipment, etc.
The LKP is important as it gives management a datum to start more formal planning from,
a location to start tracking from, a location to acquire or re-acquire the DOT, and confirms
that they were likely there at some stage.
This is the Point Last Seen
The PLS is based on a physical sighting of the subject. It is important because it can give
us all the same information as a LKP as well as a physical and likely psychological
description of the subject at that time, their equipment, probable intentions, etc
This is the Direction of Travel
The DOT can be established by visual tracking teams, dog tracking teams or by the
plotting of clues as they are found. It is important because it assists in defining or refining
the probable search area, assists management in deciding where to deploy resources,
speeds up the likely time to locate the subject etc
This is the Probability of Detection
The chance of the subject (or object) being detected, by a search team if that subject or
object was in the area being searched. Usually expressed as a percentage or likelihood
value.
This is a Decision Point
By definition a DP is “a location that a subject makes a conscious or unconscious decision
about their choice of route”. DP’s are important because they are often the start of a LP’s
‘lost’ process and are important locations to deploy expert visual or dog tracking teams to
establish probable DOT.
This is Lost Person Behaviour
LPB is the statistical data of what similar previous subjects have done. It is important
because it tells us how previous subjects behaved whilst lost, how far they travelled,
historic find locations and what search methods have previously worked. All this
information can assist us in tailoring the SAR response for the current lost party.
This is Relevance of Clue expressed as a percentage
This is a subjective determination of the relevance of clues or items found by the search
teams based on information they have at that point in time. Actual relevance may only be
determined with good investigative work by members of the management team.
Management Terms that may also be used and are useful to know :
POA
POS
IPP
This is the Probability of Area
The POA value gives the mathematical probability of the subject or an object being in an
area
This is the Probability of Success
POS measures the probability of successfully locating the subject and/or objects in an
area or segment.
POA x POD = POS
This is the Initial Planning Point
The IPP is the initial location from which incident management teams will start the formal
planning process. It is a datum – usually the LKP or PLS..
Page 2 of 8
Lost Person Behaviour
As SAR teams, we need to understand the people we are searching for, what they do, and where
they go once they realise they are lost.
Lost Person Behaviour (LPB) is worldwide-compiled statistical information and characteristics collated
from previous lost subjects that are grouped into common categories. This information includes what
they have done, where they might have gone, travel routes, did they seek shelter, etc. This data can
then be used to try and predict where the current subject may go and what they may do.
This is the starting point for a search and can indicate areas of higher probability for
checking first. However it is NOT an absolute and we must be flexible as circumstances change.
The Missing Person Matrix
The Missing Person Matrix is an important tool in providing us with a way to determine best search
methods based on the expected state of the missing person. A seriously injured or unconscious
person may be much more difficult to find than one who is simply lost as they will not be able to do
much to help searchers. Therefore we can categorise the possible state of the missing person
depending on their mobility and ability to respond to searchers.
Mobile
Immobile
Responsive
Unresponsive
The important point to remember is that the state of the missing person can change over time due to
weather conditions, time being lost, injuries, emotional state, etc. Generally over time a lost person
can move from being:
Responsive and Mobile to Unresponsive and Immobile
Passive Searching
Passive searching is a tool used when the time lapse since the person went missing has been short
or if it considered the subject is still mobile.
Attraction is where the missing person is attracted to you (or to a known location)
Confinement is establishing a specific perimeter boundary to reduce the chances of the subject
leaving the search area and also to stop the search area expanding any further.
Passive searching is waiting for the subject to
• Come to the searchers
• Attracting the subject to the searchers
• Attracting the subject to a known location.
Things like
• Visual attractants such as light flares, fires, police car flashing lights, or smoke
• Sound attractants like whistles, sirens, gun shots, horns
• Camp-ins where searchers wait at DP’s for the subject
• Confinement at huts, prominent points, river junctions, etc
• Observation points at high locations with a good field of view
• Man-made track traps
• String lines across tracks with a note attached
• Media broadcasts
• Aircraft fly-overs
Page 3 of 8
The 300m Circle
The 300m circle is not a circle (per se) nor is it derived from LP statistical data. It is an area that
encompasses natural boundaries about a 300m radius from the LKP of the subject. This is a highly
clue-rich environment with a likely high density of clues and if not finding the lost party within the
circle, clues are likely to be able to indicate a direction of travel. This then becomes a crucial piece of
information for the management team in being able to refine the search area and to assign higher
probability areas in the search plan.
Experienced Track and Clue Aware searchers (or teams) are deployed to this area early on in the
search and the area must be covered very well.
Important points
• Segment into manageable areas
• Careful, progressive, thorough observation
• Team choice of search method to suit the circumstance
• Careful mapping and recording of data
• STOP Stop, Think, Observe, and Plan
• Differentiate and mark your own contamination
• Focus on finding the lost party or the clue
Sound and light
Using sound and light has the potential to increase the effective search area beyond the visual
limitations of the actual searchers. It assumes that LP’s are responsive and want to be found.
Use of sound during daylight and sound/light during darkness is:
•
•
•
•
•
quick and easy to implement
can task smaller teams
works in most weather conditions
flexible and applicable to mixed type terrain
capable of achieving high POD% for responsive subjects
Types of Sound
Usually sound is generated by whistles and voice is not used except when tasked so by the IMT.
Through trial and error it has been found that a pea-less whistle works best and in the field we use
either the Fox 40 or the Storm whistle. Various other devices have been trialled but are not so
effective in the NZ bush.
Spacing
A key feature of either the Line or Sweep technique is to have the team members well separated. As
the searchers get closer together the sound and light generated by the team is more likely to be
affected by similar vegetation and land form. Maximising the spacing increases the distribution of
sound and light and increases the angles which the subject’s responses can be heard. This also
reduces the impact of any dominant vegetation area and/or terrain. Ultimately the team spacing is
going to depend on the circumstances, the weather, vegetation, terrain, resources available and the
desired probability of detection. Spacing is a matter that team leaders will need to decide relative to
their team tasking.
Use with other search methods
It is easy for teams to stop and use their tracking skills at decision points or sign-cut as they move
along a linear feature
Page 4 of 8
Sound Line
The use of Sound Lines is often the
first choice in the initial phase of an
operation.
Sound lines are deployed along
any linear feature such as roads,
tracks, streams, ridges, and fence
lines.
In use:
• can be used in a team of
three – leader in middle
• establish the likelihood of
hearing a voice response
and set team spacing accordingly
• allow for cross-winds and use lower value for spacing
• consider the circles and allow for overlap
• GPS waypoint start point and end point
• STOP = 2 loud short blasts from leader
• Turn down radio volume and turn off torches
• Count down from 5 secs, block ears, and all blow whistles together for as long as possible
• Listen for 15 secs, cupping hands to ears, and opening mouth (this opens the ear canal)
• GO = 1 loud blast from leader to move forward again
• Leader judges distance travelled and calls next stop ( 110-120 paces = 100m on good tracks)
• 5 loud short blasts by any team member = COME TO ME
Sound Sweep
A Sound Sweep is used to search large tracts of land
such as farmland, paddocks, bush, or forests where
team members each follow a pre-set compass
course.
It can be used where an initial response has been
heard from a Sound Line to sweep down on to the LP.
In use:
• can be used in a team of three – leader in
middle
• establish the likelihood of hearing a voice
response and set team spacing accordingly
• allow for cross-winds and use lower value for
spacing
• think about terrain and team safety
• consider circles and allow for overlap
• GPS waypoint start point and end point and
agree on bearing line
• endeavour to keep in line abreast
• STOP = 2 loud short blasts from leader
• Turn down radio volume and turn off torches
• Count down from 5 secs, block ears, and all blow whistles together for as long as possible
• Listen for 15 secs, cupping hands to ears, and opening mouth (this opens the ear canal)
• GO = 1 loud blast from leader to move forward again
• Leader judges distance travelled and calls next stop
• 5 loud short blasts by ant team member = COME TO ME
Page 5 of 8
Sound Light Line and Sound Light Sweep
These methods are exactly the same as Sound Lines and Sound Sweeps with the addition of light at
night to aid as an attractant.
Hand held LED torches with a reasonably
focussed beam are ideal and a headlamp to
find your footfalls is also good.
The concept is to light up the underside of
the bush canopy as you move along so that
a LP may see the flood of light.
In use it is a slow deliberate sweep in a
figure of 8 motion as you move along
between whistle stops.
For night searching it is a good idea to have a red cycle lamp on the back of your pack to aid fellow
team members.
Purposeful Wandering
Purposeful wandering is usually used in searching for unresponsive and immobile subjects or when
looking for clues or objects. It combines the best of a rigid search system with the instincts of a well
trained searcher while allowing freedom to think and to apply their other skills.
Most search areas or segments will require multiple
sweeps to insure sufficient coverage of the
segment. Multiple sweeps are generally conducted
across the narrower aspect of the segment and are
more likely to produce a higher POD %.
Terrain will also be a major consideration in which
way to sweep, but it is generally easier on personnel
to contour rather than up and down slope.
Searcher Spacing
In the simplest form, spacing can be used to control the expected POD %. Critical separation is used
to assist in defining an approximate ranging width for each wanderer taking into consideration the
terrain and vegetation. More open terrain would mean a wider wandering range, dense vegetation or
difficult terrain would mean a narrower wandering range.
Critical Separation
This is found by laying an object on the ground that is similar to that which is being searched for.
Each searcher circles round it, moving outwards until it appears just on the limit of their peripheral
vision. The average of the distance back to the object multiplied by 2 is a good indication of the
spacing needed between searchers. Can be known as a ‘Rain Dance’.
Page 6 of 8
Coverage
The base reason for purposeful wandering having a high POD% is because of the ability of the
wanderers to actually wander.
By wandering randomly within the range, as well as to
places of interest, a high coverage factor can be obtained
due to many areas within that range being searched more
than once.
In the diagram coverage is equal to or greater than 100% the total area searched including areas searched more than
once is greater than the segment area. This coverage would
give an approximate POD of 63%.
However this high POD will only be obtained while the
wanderers are actually wandering. Over time, on long
sweeps, or as the wanderers tire, the wandering decreases.
This will have the effect of lowering the coverage factor and therefore directly affecting the POD %.
Methods
The method employed depends on the team size, the terrain, the desired POD%, time available,
POA%, etc.
A 3 person team is usual with the team leader in the middle following a compass course with 2
‘wanderers’, one each side. The leader can ‘hang back’ a little, controlling the tasking with good,
constant communication between team members.
However, often the first sweep will use a natural boundary to follow on one side.
Here the compass bearer is placed on one side of the team to mark one
boundary where a natural border (a stream, vegetation change, fence etc)
exists on the other side.
The compass bearer marks the outside boundary with dazzle, flagging
tape, or a hip chain string as they go. This provides clear, defined
boundaries for areas searched.
It is then simple for the team to swing around when they reach the limit of the search area and
complete a return parallel sweep or for another team to join
in alongside.
.
It does have some drawbacks in that if the TL is in the
middle more time is spent managing the team than actually
searching (POD% will suffer).
If the TL is the compass bearer it becomes difficult to
communicate with the other outside wanderer and insure
coverage.
There can be many adaptations to this base method with teams of up to 6 or more searchers
but the same principles apply irrespective.
Page 7 of 8
Probability of Detection (POD%)
The retrospective POD% that a field team reports when a segment has been searched, is an
important measurement tool used by the IMT for allocating further resources to areas where the lost
subject is likely to be found.
POD is a subjective, retrospective consensus measurement, judged by all team members, of the
likelihood that the subject would have been found in the area if they had been there.
It is expressed as a % based on effort, searchers effectiveness, weather, terrain, forest density, and
so on, and is reached by all members of the team expressing an opinion as to the success of the task
they have just undertaken.
Measurement
If it was a person search and there were 10 unresponsive, immobile persons in the tasked area and
you feel you would have found 4 of them then the POD% is 40%.
This is relayed to IMT and they then use that information to re-assign the probability of that particular
area and therefore the allocation of further resources. As POD%’s come in from the various teams a
cumulative POD can be calculated to identify the factors affecting the search success.
An important search theory tool:
Probability of Area x Probability of Detection = Probability of Success
POA% x POD% = POS%
Segmenting the Search Area
Page 8 of 8