When objects are missing in the marine environment, whether the objects are persons, vessels, or containers, primary concerns are where the objects will travel and the most probable search area. These questions must be answered rapidly as they often involve life and death situations. SARMAP's user-friendly, Windows-based search and rescue model system makes this possible. SARMAP facilitates search and rescue planning for SAR professionals in both industry and government agencies.

SARMAP provides rapid predictions of the movement of drifting objects based on their last known position (splash point) and object configuration (drift behavior). A database of drift behavior based on the latest US Coast Guard research is provided with the system for a variety of objects. Using these data in combination with the winds and currents in the region of interest, SARMAP calculates the most probable search area.

Simulations are typically performed for a variety of postulated accident sites and drift characteristics. This series of simulations provides an envelope of likely search areas. Search & Rescue Units (SRUs) may be assigned to the search area based on speed, endurance, and range, and the Probability of Success (POS) for a particular search configuration determined.

When floating debris (e.g., life jackets, luggage, boat/aircraft parts, etc.) Is found that can be definitively linked to the lost object, it is possible to identify the probable location of the accident site (source of the debris) by using the model in the backtrack mode. Each object is assigned representative drift characteristics and simulations are run backward in time starting at the observed siting or retrieval location of the debris. Environmental data are derived either from observations or hindcasts for the time period of interest.

Since the quality of model predictions depends on the quality of the environmental data, a suite of tools allow the user to handle environmental data efficiently. A variety of graphically based tools are included which allow the user to:

SARMAP includes an interactive mapping/Geographic Information System (GIS) that allows the user to enter, or import from external GIS sources, a variety of geographic data such as Search & Rescue resources, GPS reports, and key coastal features.

The GIS database stores the home base locations of all available Search & Rescue Units (SRUs) for the region. Each SRU database entry stores information about the SRU's speed, endurance, and range. Users can simply "drag" an SRU to a predicted Search Area and the system will calculate its on-scene endurance, time of travel, search leg coordinates, etc.

The GIS engine supports display of ARCVIEW/ARCINFO shape files directly, and provides import tools for MAPINFO (MIF/MID) export formats. SARMAP may also be run as an ARCVIEW extension.

Sarmap extension for ArcGIS9

SARMAP supports commercial nautical charts including:

• BSB NOAA Charts
• MapTech Charts
• NDI Charts
• NOS Charts
• British Admiralty (ARCS) Charts
• S57 Charts
  

A global map database CD is available for use with SARMAP. This allows users to immediately set up new areas anywhere in the world from the Digital Chart of the World (DCW), the World Vector Shoreline (WVS), or NOAA's medium resolution coastline (U.S. only). The integrated SRU deployment tool in SARMAP rapidly estimates the Probability of

Success (POS) for a given search scenario. The number of active SRUs, their operating constraints, and the search conditions are factored into the POS. Different search patterns can be rapidly visualized and assessed.

Search and Rescue Model: Technical Overview

The SARMAP Search and Rescue model (SARMAP) is based on the search planning methodology set forth in the National Search and Rescue Manual of the U.S. Coast Guard. It is intended for use in marine incidents.

The model determines the most probable location of the search object, also known as datum, and a search area around the datum. The position of the datum changes with time due to winds and currents acting on the object. The search area increases with time and is related to the drift of the datum.

Types of Solutions

The SARMAP user interface provides a list of approximately seventy possible search objects. Each search object has pre-defined values that define its drift characteristics. These values are based on recent U.S. Coast Guard research. Multiple search objects can be selected for tracking in a single simulation.

The user can select from three types of solutions: IAMSAR, Monte Carlo random walk, and Monte Carlo random flight. All three solutions predict approximately the same search region, but the IAMSAR solution typically recommends the largest search area. The two Monte Carlo solutions produce very similar results and smaller search areas.

The IAMSAR solution tracks three separate datums for each selected search object. One datum moves directly downwind while the other two datums move to the left and right, respectively, of downwind at a divergence angle specific to the search object. The search area is computed to encompass all the datums. Computation of the search area is described in the Search Area section below.

The Monte Carlo random walk solution tracks multiple particles representing possible trajectories of the search object. The user can specify the number of particles to be used. Each particle moves according to downwind and crosswind parameters specific to the search object. A small random component is added to each particle's movement each time step. The maximum magnitude of the random motion depends on the type of search object. At selected intervals a percentage of the particles are assumed to jib (i.e., particles that were moving to the right of downwind will change to move to the left of downwind, and vice versa).

The Monte Carlo random flight solution is similar to the random walk solution. The difference is in the determination of the random component of motion. The random flight solution incorporates a time history into the random motion, such that the present random motion is affected by past random motion. This prevents particles from having a random movement to the north at one time, and a random motion to the south the next time step.

The search area for the Monte Carlo random solutions is defined by the extent of the predicted particle locations. A grid placed over the particles shows the probability of the search object being in each cell of the grid, based on the number of particles in the cell.

Datum Transport

Transport is the vector sum of three forces acting on the datum: sea currents, wind currents and leeway. Each is described in more detail below.

Sea currents are due to the large-scale movement of ocean waters. The model uses spatially and temporally varying currents stored in data files and specified by the user. These files typically include tidal currents and/or mean background (over time scales of a season or more) currents.

Wind currents are wind-driven currents generated by winds acting on the water surface over a period of time. Wind currents are not important in nearshore areas, but should be calculated for water depths greater than 30 m and distances greater than 30 km from shore. The user selects whether or not to include wind currents as a forcing parameter. SARMAP calculates the wind current based on the wind history for the previous 48 hours. Using the average wind speed over 6-hour blocks, the resulting wind current is computed by applying time- and latitude-dependent speed and direction corrections to the wind speed. The contributions from each 6-hour period are added vectorially to give the local wind current.

Leeway is the drift resulting from winds blowing against the exposed (above water) surfaces of the search object. The leeway is dependent on the type of search object. Objects with more exposed area above the water line are more strongly affected by leeway, while completely submerged objects are assumed to have no leeway. Leeway drift is a modification of both the wind speed and direction. The SARMAP interface includes values of the parameters used in leeway calculations for over seventy search objects.

Search Area

For the IAMSAR solution, the search area is calculated by first defining a search radius centered on each datum. The search radius includes the probable errors inherent in estimating the datum's drift and initial position. The drift error is calculated as a fraction (typically 0.3) of the total drift. The initial position error depends on the navigation method used by the search object.

Once a search radius has been calculated for each datum, a rectangle circumscribing all the search radii is determined. This represents the total search area. The search area may also be increased by a safety factor specified by the user. Recommended safety factors increase with the number of searches done, from a value of 1.1 for the first search to a value of 2.3 for the fourth and successive searches.

To see an animated SARMAP scenario, click here.

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