Modeling the Movement of Lost People

The mobile command station of Podhalanska Group.

Using a database created with statistics gleaned from previous explorations allows Podhalanska Group (PG) to increase the likelihood of finding lost persons. The implementation of data from PG's database in its GIS allows rescuers to model the movement of lost people in the area of interest. In exploratory analyses, Podhalanska Group uses the following parameters.

Distance from IPP

The initial planning point (IPP) is a point used for search planning. The IPP is very often the point a person was last seen (PLS). Planners usually define PLS as a person's last known point of travel, such as a parking lot. The total search area is designated by a circle, in which the likelihood of finding a person in the field is approximately 95 percent (that is, 95.5 percent of the values lie within a distance ≤ 2 sigma [standard deviation] from the expected value, a normally distributed data assumption). The circle is not the final frontier of search but can be further defined based on terrain features, and it should be suitable for a specific exploration scenario.

Elevation Change from IPP

Technicians compare the recorded IPP with the recorded location where the person was found and determine the elevation difference between these two points. This method distinguishes three zones: the distances uphill from the IPP, downhill from the IPP, and at the same level as the IPP. These statistics do not take into account the total elevation changes. Vertical differences in height are greater in dry domains than in temperate ones. Searching above the IPP is usually associated with an attempt to find telecommunication network coverage.

"Fast three" method allows greater flexibility in the choice of route exploration in comparison with other methods.

Mobility

Mobility measures in hours the amount of time a missing person can potentially be moving. Studies show that the missing are mobile two times longer in dry domains than in temperate ones. GIS enables the creation of areas of mobility. Moreover, analysis of movement time in the search area, together with information of the route length, allows Podhalanska Group's rescuers to specify the speed of movement.

Dispersion Angle

Calculating the dispersion angle offers another effective method of determining the likelihood of successful rescue operations. This method identifies three points in the search area: the initial planning point, discovery point, and destination (the direction of travel) point. There is no evidence that the farther a person moves, the smaller the dispersion angle. However, there is a hypothesis that terrain affects the dispersion angle. In flat terrain, a lost person usually moves faster, possibly increasing the distance from the initial planning point.

Location

PG's planners use the data from previous successful rescues to decide which area to explore. On the basis of such data, rescuers create the finding lost person areas.

The Polish Carpathian Mountains.

PG takes into account the following categories of objects affecting exploration: artificial objects (buildings, parking lots, etc.); roads; drainages and surface water (lakes, canals, ponds, etc.); shrubs, bushes, forests, rocks, and fields (also golf courses, vineyards, etc.); and line features (except roads and drainages).

According to statistics, most people are found near line features and fields.

Track Offset

The track offset (distance from line features) is the shortest perpendicular distance from the planning route. The distance from the lost person to line features is analyzed. For this purpose, a buffer zone, such as the distance from a road (100 m), is created. On the basis of data gathered from past explorations, the likelihood of finding the lost person is assigned to the buffer zones. This method takes into account only cases of loss past linear features. Cases of finding lost persons on roads and other linear features are analyzed within the location statistics. PG rescue teams can be assigned to search the designated buffer zones, so it is important to create buffer zones with low values (distance units); this allows more precise exploration of the area.

The total search area is a circle in which the likelihood of finding a lost person is 95 percent.

Exploratory Scenarios

Each case requires an examination of loss scenarios. It should be stated whether a person is lost, is a crime victim, or has a sprained ankle. The loss scenario is often determined on the basis of an interview with the family and circumstances of the disappearance.

Koester has identified as many as 41 different search categories. The classification of a missing person in a particular group can significantly hasten exploratory action.

For more information, contact Elzbieta Filipkowska, GIS specialist, Esri Polska (e-mail: efilipkowska@esri.pl, tel.: 0048-660-045-626); Robert Koester, author of Lost Person Behavior (e-mail: Robert@dbS-sar.com, tel.: 1-434-293-5502); or Rafal Chrustek, deputy head of Podhalanska Group (e-mail: rchrustek@gopr-podhale.pl).

See also "Lost and Found in the Polish Carpathian Mountains."