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PDO at the Team Level  SAR SKILLS: P ROBABILITY OF DETECTIONB Y JOHN MINDOCK OF CIBOLA SARWhat is Probability of Detection? Informal Definition: The probability that your team noticed the subject in the area you searched. Also can be depicted as the percentage of the assignment area (big enough for a person to hide in) that you actually looked at while searching. It is NOT a measure of the quality of a team's effort, nor of their proficiency as searchers. Overview During a debriefing after an assignment, field teams are commonly requested to report their `Probability of Detection'. Often this is divided into two types - Responsive and Unresponsive. Often, the POD is formulated by using `gut feeling' based on experience, wishful thinking, and some idea of what was expected in the first place. Note - POD's higher than 80% are defacto counted as 80%, perhaps due to legal concerns. What is Unresponsive POD? Unresponsive POD is simple to fathom - if the subject was lying within your search area, but unable to respond to you, what's the chance that you saw him? This usually is a function of the size of the area, the number of searchers, the rate of travel, the terrain/flora, the subject's clothing, and the thoroughness of the search tactics. Weather and darkness also can figure into the calculation. A subject may be unresponsive because of death, unconsciousness, weakness, fear of searchers, or evasion. What is Responsive POD? Assuming that the standard attraction techniques (yelling, whistles) are used, what is the probability that the person was in the area you searched, and yet you did not hear him responding to you? This measurement is a function of the size of the search area and the number of searchers. Rate of travel, terrain/flora, and thoroughness are not really factors one way or another. Weather (such as high winds) may figure in, but darkness has no bearing. Responsive POD is never less than unresponsive POD, for obvious reasons. What is the Significance of the POD to the Incident Management? Subsequent to the `initial attack' portion of a mission, the territory being searched is subdivided into portions called `search segments'. After a certain amount of effort over several operational periods, mission management develops a strategy where they start eliminating search segments. This is often used to justify a decision to suspend the mission. The criteria for suspending a mission are somewhat subjective, but for this paper let's say that much of that decision is based upon reaching 75% POD in all segments within the subject's probable range of travel. This range is determined by statistical analysis of many missions nationwide with similar subjects, as described in documents used by Incident Management for planning the search. At this point, the teams being deployed notice a change in assignment directives, hearing instructions like `search this segment to a 80% POD' instead of `go up such and such trail'. The nature of POD has shifted to a pre-deployment specification, as opposed to an assessment of the results upon return. The decision to suspend a mission will occur after a number of operational periods, and the subject will have been in the elements for a significant time. The assumption at that time will be that the subject is no longer able to respond. During this phase of a mission, the assignment to search a segment at `x' POD really means an unresponsive POD. This normally goes unsaid during the team briefings, but it is the only sensible interpretation, i.e., if the person is still highly likely to be responsive, we wouldn't dare consider suspending the search yet. Management Usage for Responsive POD There are scant few scenarios where this is used to make management decisions. Perhaps if a team had not used common attraction techniques (whistles, etc.), or if there had been a howling wind, a low responsive POD might instigate a re-search of the area. Another scenario would be where searchers spread out too far to hear each other and the subject might be in-between. If your team returned with a very high responsive POD in the early stages of a mission (when the subject might still be likely to be responsive), mission management might decide to send teams into other high-potential areas instead of researching your area in an `area search' mode. Management Usage for Unresponsive POD From a practical standpoint, unresponsive POD is more likely to have an influence on management decisions than responsive POD does. A search segment can be eliminated from further searching if the area has been covered to a high unresponsive POD. There is a somewhat rigorous set of cascading mathematical calculations that depict the actual cumulative POD's and the prescription for elimination. As mentioned above, the nature of the assignments change to where a high unresponsive POD is requested prior to deployment. This dictates the search tactics, and the thoroughness to be applied. Efficiency vs. Thoroughness In previous paragraphs, it was mentioned that thoroughness is a factor in POD. Lack of thoroughness in this sense does not imply sloppiness, laziness, or some other less-than desirable behavior. Thoroughness and efficiency are different aspects of the search spectrum, and neither is right (or wrong) by itself. Efficiency refers to searching the largest territory in a minimal amount of time, using limited personnel resources. Thoroughness means ignoring time/personnel constraints and looking `everywhere'. In general, efficiency implies rather swift passage while thoroughness denotes a slower pace. Hasty teams are intended to perform `efficient' searches as opposed to `thorough' ones. Looking behind every bush, rock, and log (in an effort to be extremely thorough) is contradictory to the theory of using hasty teams, and represents improper execution for their assignment. Since hasty teams are responsible for 80% of all finds, it is important to perform the proper techniques during such an assignment. A corollary to this is that a low POD is acceptable (indeed, often expected) of hasty teams. On the other hand, `area search' teams are expected to be thorough, and generally are counted upon to return with a very high POD. Failure to return with a high POD may require the segment to be re-searched. Continued
Probability of Area (POA) As a simplified example, a fisherman is more likely to be near the stream than on top of the hill, so the POA's of areas near the stream would be higher than the ones near the top of the hill. However, after the areas adjoining the stream have been searched to high Unresponsive POD's, their POA's may be lowered and the top of the hill area's POA increased. In theory, teams assignments correspond to the POA of the areas, with highest POA areas covered first. In reality, Incident Management does not have enough time to chitchat about POA's in the `initial attack' phase of a mission, so those assignments are made on intuition and history rather than a formal POA strategy. Later assignments might be more explicitly based on POA considerations. Probability of Coverage (POC) [Ed. Note added 27 Feb 2006: The "POC" referenced here was defined and used in a 1996 article in the NASAR journal "RESPONSE", and its usage was being encouraged in New Mexico SAR management at the time this article was written. Unfortunately this usage is in conflict with the usage of the acronym "POC" in all established literature on search theory since World War II, in which "POC" is used for "Probability of Containment", a synonym for "Probability of Area". The usage described below is not standard and is no longer in use. Please refer to our more recent article on Search Theory and the references therein.]This is a predetermined set of values for Unresponsive POD, based on the factors that influence POD. It attempts to constrain the incoming POD's from field teams within the realm of reality. A simple illustration: a team of two searchers covering a six-square mile `difficult terrain' area in two hours in snowy nighttime weather should equate to a low POD. If the team returns with a much higher POD, Incident Management can supersede their POD estimate with that prescribed by the POC tables. Another application of POC would be to tell a team of four people to search an area of four square miles, and do it for six hours. Using the POC tables, this would theoretically ensure that the team got a POD of `y' %, which might be more legally defensible than any subjective estimate the team might provide on their own. Separation Types Unless Incident Management specifies otherwise, visual separation is the tactic expected of teams in an area search mode. POD for visual separation would usually be larger than that for critical separation. Terrain Types (easy, moderate, difficult) Rate of Progress Estimating Responsive POD Low (0 - 25%):
There are many more factors in this estimate (See previous mini-lesson). Low (0 - 25%)
High (70 - 90%)
This exercise is intended to give one a `feeling' for the rate of progress that 20% POD and 80% POD searches entail. Find an area where there are many boulders, trees, and/or bushes. Search the area looking behind only every fifth obstacle. Record your time for this, a 20% POD search. Now return the other way, looking behind four-out-of-five obstacles. Record the time for this, an 80% POD search. In theory, it should take @4 times as long as the 20% approach. (Actually, since parts of your search area are visible without looking behind an obstacle, the POD's would be somewhat higher than 20% and 80%.) Self-quiz on POD - PART 2
Our thanks to John Mindock of CIBOLA SAR in Albuquerque, NM
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