Forensic Science International 231 (2013) 306–316

Review article

Detecting submerged objects: The application of side scan sonar toforensic contexts

John J. Schultz a,*, Carrie A. Healy a, Kenneth Parker b, Bim Lowers b

a University of Central Florida, Department of Anthropology, 4000 Central Florida Boulevard, Orlando, FL, United Statesb Orange County Sheriff’s Office Marine Unit, Orlando, FL, United States

Contents

1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 307

2. Water search methods. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 307

2.1. Winthroping . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 307

2.2. Dive teams . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 307

2.2.1. Benefits and limitations of using divers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 307

2.3. Diver-held geophysical tools . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 308

2.4. Remotely operated vehicles . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 308

2.5. Cadaver dogs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 308

2.6. CHIRP sub-bottom profiler . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 308

2.6.1. Benefits and limitations of using a CHIRP sub-bottom profiler . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 308

2.7. Ground penetrating radar. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 309

2.7.1. GPR methodology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 309

2.7.2. Benefits and limitations of using GPR . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 309

2.8. Side scan sonar . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 309

2.8.1. Side-scan sonar methodology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 309

2.8.2. Side scan sonar imagery features . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 310

2.8.3. Operation of side scan sonar. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 311

A R T I C L E I N F O

Article history:

Received 30 May 2012

Received in revised form 18 January 2013

Accepted 16 May 2013

Available online 6 July 2013

Keywords:

Forensic geoscience

Submerged object searches

Submerged search methods

Side scan sonar

GPR

A B S T R A C T

Forensic personnel must deal with numerous challenges when searching for submerged objects. While

traditional water search methods have generally involved using dive teams, remotely operated vehicles

(ROVs), and water scent dogs for cases involving submerged objects and bodies, law enforcement is

increasingly integrating multiple methods that include geophysical technologies. There are numerous

advantages for integrating geophysical technologies, such as side scan sonar and ground penetrating

radar (GPR), with more traditional search methods. Overall, these methods decrease the time involved

searching, in addition to increasing area searched. However, as with other search methods, there are

advantages and disadvantages when using each method. For example, in instances with excessive

aquatic vegetation or irregular bottom terrain, it may not be possible to discern a submersed body with

side scan sonar. As a result, forensic personnel will have the highest rate of success during searches for

submerged objects when integrating multiple search methods, including deploying multiple

geophysical technologies. The goal of this paper is to discuss the methodology of various search

methods that are employed for submerged objects and how these various methods can be integrated as

part of a comprehensive protocol for water searches depending upon the type of underwater terrain. In

addition, two successful case studies involving the search and recovery of a submerged human body

using side scan sonar are presented to illustrate the successful application of integrating a geophysical

technology with divers when searching for a submerged object.

� 2013 Elsevier Ireland Ltd. All rights reserved.

Contents lists available at SciVerse ScienceDirect

Forensic Science International

jou r nal h o mep age: w ww.els evier . co m/lo c ate / fo r sc i in t

* Corresponding author at: Department of Anthropology, Phillips Hall, 309, University of Central Florida, 4000 Central Florida Boulevard, Orlando, FL 32816, United States.

Tel.: +1 407 823 1180; fax: +1 407 823 3498.

E-mail address: John.Schultz@ucf.edu (J.J. Schultz).

0379-0738/$ – see front matter � 2013 Elsevier Ireland Ltd. All rights reserved.

http://dx.doi.org/10.1016/j.forsciint.2013.05.032

J.J. Schultz et al. / Forensic Science International 231 (2013) 306–316 307

2.8.4. Benefits of side scan sonar . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 312

3. Case studies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 312

3.1. Equipment. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 312

3.2. Case study one . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 313

3.3. Case study two . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 315

4. Discussion and conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 315

Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 316

References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 316

1. Introduction

While death investigators and crime scene personnel arefrequently employed in searches for buried bodies and evidencein the terrestrial environment, they are also involved in watersearches for a variety of objects such as human bodies, animalbodies, weapons, contraband, explosives, vehicles, planes, andboats. For example, water searches may involve search andrescue efforts due to boating accidents, swimming accidents,downed aircraft, sunken ships, sunken automobiles, as well asthe disposal of evidence and bodies in water environments.While successful forensic searches generally integrate multiplesearch methods, commonly incorporated methods for sub-merged bodies and evidence include draining the body of water,using underwater cameras deployed on remotely operatedvehicles (ROVs), using dive teams, winthroping, or using cadaverdogs in a boat.

In recent years, forensic personnel involved in water searchand rescue applications have integrated geophysics into theirsearch protocols [1–10]. Waterproof hand-held geophysicaltools are commonly used and can be operated by divers whensearching for submersed metallic weapons. It is also possible todeploy divers or an ROV with a camera to investigate suspiciousfeatures detected after first performing a geophysical search of alarger area with ground penetrating radar (GPR) and side scansonar from a boat. Ground-penetrating radar has been success-fully used to locate submerged bodies and evidence [6–8], andthe use of side scan sonar has been gaining in popularity for lawenforcement agencies in recent years [1–5,9,10]. In aquaticenvironments, geophysical tools have additional benefits, suchas decreasing the potential risk to divers, allowing searches tocontinue after nightfall, and decreasing the sediment distur-bance that would be caused by divers. It is important to notethat geophysical tools are generally used in conjunction withother search methods. For example, after a target is located in awater environment, the target is generally investigated andretrieved by divers or a remotely operated vehicle (ROV)[1,4,9,11].

The purpose of this paper is to provide an overview of thevarious search methods available to forensic investigators whensearching for submerged objects, and to discuss how theintegration of multiple search methods increases the successrate of searches. The advantages and disadvantages of thevarious search methods will be provided, and finally a number ofsuccessful body recoveries in lakes by the Orange CountySheriff’s Office (OCSO) Marine Unit in Florida, U.S. will bediscussed. It is important to note that there will be a greateremphasis placed on side scan sonar, as this geophysical methodis the focus of the two case studies provided in this paper and hasbecome a popular geophysical option for law enforcement watersearches. For a detailed overview of the various geophysical toolsused for searching water environments refer to Bowens [12] forunderwater archeology methods and to Parker et al. [6] for anoverview of the methods used to search for forensic evidence andbodies.

2. Water search methods

When investigators are faced with searches for submerged objects, there are a

number of traditional methods that can be utilized. In small bodies of water such as

a pond, it may be possible to drain the water to conduct a thorough search of the

pond bed to locate evidence, a submerged body, or disarticulated body parts. With

larger bodies of water and bodies of water with a current, such as rivers, draining is

generally not an option because of the expense and challenges involved. While

there are a variety of search techniques to use for the water environments, there are

advantages and disadvantages for each technique. The search technique, or

combination of techniques, most applicable to a specific recovery will depend on a

number of site variables including the type and size of the water environment, the

type of bottom terrain, the presence or absence of aquatic vegetation, the weather

conditions, as well as the time of day to perform the search. Therefore, a thorough

knowledge of the search tools available will allow investigators to select the most

appropriate method, or integrate a combination of search methods.

2.1. Winthroping

The archeological survey consists of visually searching a landscape, which can

include various search patterns, for clues that would indicate a clandestine burial or

an archeological site, and is a common noninvasive search technique employed by

the forensic archeologist or archeologist [13,14]. This technique of evaluating a

landscape is particularly important for the archeologist when trying to assess a

landscape for archeological sites [15]. Forensic archeologists will commonly

visually search a landscape when they are performing clandestine grave searches

and when searching for dispersed skeletal remains. Visual searches for human

remains and unmarked graves generally involve searching areas using common

search patterns presented in a variety of forensic archeology texts [4,13]. When

dispersed skeletal remains are located, the pattern of dispersal will be studied to

determine the optimal trajectory of dispersal that will need to be searched when

trying to recover additional missing bones and teeth [14]. At the same time, proper

landscape evaluation for archeological sites may involve multiple visits to an area,

which may not be possible with the timescale of a forensic case [15].

More recently, the search technique winthroping has received attention for

forensic search inquires. This search technique was originally introduced as a

counter-terrorism method in Northern Ireland to locate weapons caches [15].

Winthroping studies the prominent landscape features or markers that may have

been used as guide points by the offender [15,16]. For example, the investigator

studies the landscape to determine possible routes followed by the perpetrator in

concealing a body or forensic evidence. Further, the method assumes that the

process of burial is not a random phenomenon, but relies on fixed points. These

fixed points, or landscape features, may be used by the offender for entry and exit

from the body disposal location or for the purpose of future recognition by the

offender [15]. Investigators should consider winthroping methods when trying to

discern access routes used by offenders that were attempting to conceal submerged

objects in water. The recognition of specific landscape features may be important

for forensic personnel when discerning the entry point that objects were dumped

into the water. At the same time, investigators can also consider current and wind

conditions when determining the trajectory that submersed bodies may have

traveled, and to integrate water methods when searching for submersed objects.

2.2. Dive teams

One of the most commonly employed methods to search for submerged objects

involves the use of divers [1,12,17,18]. Divers will generally employ a variety of

search patterns based on the underwater terrain and the size of the target. An

overview of the various search patterns performed by divers is provided by a

number of authors [1,12,17,18]. It is recommended that a dive team should consist

of a minimum of three divers for safety reasons. Divers should always work in pairs,

and it is prudent to have a third diver on the boat ready to deploy if one of the

working divers requires assistance.

2.2.1. Benefits and limitations of using divers

Divers work well with other search methods such as geophysical methods by

investigating possible anomalies that have been located during the geophysical

survey. For example, if a potential submerged body is located with side scan sonar

J.J. Schultz et al. / Forensic Science International 231 (2013) 306–316308

or a water search dog, the location will be marked with a buoy for divers to

investigate the target and retrieve if a body is located.

While divers can be employed quickly for a search, there are also disadvantages

to utilizing divers for water searches. The time requirement to perform detailed

searches for larger search areas can be considerable compared to other search

methods such as side scan sonar. For example, Armstrong and Erskine [1] suggest

that the use of one sonar unit can be used to search a football-sized area much

quicker than an experienced dive team could cover in weeks. Diver experience can

also affect the success of the search [19], and therefore, divers should be trained in

effective search techniques prior to deploying on a search and recovery operation.

Divers should not work at night or during inclement weather, as the visibility of the

water or weather conditions can limit the speed to perform a search or even

prohibit the use of divers. At the same time, diver searches can decrease visibility

due to sediment disturbance. In instances of low visibility, divers may need to

search the bottom of the lake bed by hand for small items, thus increasing the time

required to search an area. Also, divers may not be able to search areas with

entanglements, such as debris or vegetation, or areas with strong currents. For

example, it may not be possible to search rivers with divers if the currents are

strong. In areas with manageable currents it may be possible to employ divers using

line based assistance or a towsled [17]. Additionally, divers can be limited by the

depth of the water and time under pressure. In instances where divers are not

available or the submersed depth of the body limits the use of divers, ROVs can be

employed in place of divers (see Section 2.4).

Diver health is another concern. A diver can encounter several health issues

related to diving, including, but not limited to nitrogen narcosis, decompression

sickness, hypothermia, hyperthermia, or injury, and are more likely to have

cognitive, musculoskeletal, and hearing issues than non-divers [12,20]. Moreover,

contaminated water increases health concerns for the diver. When there is a risk of

contaminated water, divers should utilize a dry suit and decontamination

procedures should be undertaken prior to the diver removing the suit [17,18].

2.3. Diver-held geophysical tools

Divers can also utilize hand-held sonar, magnetometers, and metal detectors to

assist them in searches for submerged objects that are large or small in size. Use of

these tools should involve a systematic grid search to ensure that the entire search

area is covered. Hand-held magnetometers and metal detectors can be used when

the targets are comprised of metal such as a discarded metal weapon. In addition,

they can also be used to locate metal objects that have become buried or are covered

with sediment. However, it is important to be familiar with metal composition

when using these tools because handheld magnetometers will only detect ferrous

metals, while metal detectors will detect both ferrous and non-ferrous material. For

underwater archeological applications, pulse induction metal detectors are

recommended for water searches involving metal [12]. The search-head of the

metal detector emits pulses of energy that produce a temporary magnetic field.

Metal objects are detected because the magnetic field persists longer in the

presence of metal [12]. When using this tool for underwater archeological

applications, it is first suggested to map all anomalies during the pre-disturbance

survey, and then to determine the approximate location of the buried object before

removal [12].

The hand-held sonar unit is available for divers to use when visibility is limited

during searches. The handheld sonar unit is wielded by a diver underwater and

aimed toward the last known direction of a target such as a body [1]. The diver

should hold the sonar as close to the bottom as possible so that the returns are more

effective. The unit projects a narrow cone of acoustic energy that will bounce off of a

reflective target such as a submerged body and will be received by the unit. The

diver can locate the target because an audio unit within the hand-held sonar

processes the returns and sends an audio signal to the diver’s earphone, creating a

change in tone based on the diver’s distance to the target [1].

2.4. Remotely operated vehicles

Another search option that is appropriate for integrating with other underwater

search methods are remotely operated vehicles (ROVs). These underwater robots

are tethered to a surface boat and controlled by a human pilot. While they are

minimally equipped with lights and a video camera, the vehicle’s capabilities can

also be equipped with other options such as a still camera, water samplers, a

multifunction manipulator or cutting arm, instruments that measure temperature,

water clarity, and light penetration [21]. The use of unmanned operated vehicles

has been increasing for commercial, military, and scientific applications [22]

because these robots can perform many of the tasks performed by divers [12]. In

addition, they can operate in deeper waters not accessible by divers, in waters with

obstructions that may be hazardous to divers, and their use underwater is not

limited by time spent under pressure [12,22]. An ROV with image-intensifiers

provides increased imagery resolution on the surface monitor than the diver can see

underwater [12]. Forensic personnel involved in the search and recovery of

drowning and accident victims have also incorporated the use of ROVs with other

search options. For example, if an obscured feature has been located with a

geophysical tool such as side scan sonar, the ROV can be deployed to image the

feature to confirm body detection before deploying divers, saving time and labor.

Law enforcement may use a small ROV unit with a video camera and lights that

can be dropped over the side of a boat during a search. The ROV can be deployed in

areas where it may not be safe for divers. The OCSO Marine Unit will often use an

ROV when performing an underwater search of bridges and piers due to bomb

threats. However, it may not be possible to deploy in murky water since it would

not be possible to visualize targets. In addition, it may not be possible to deploy

small ROVs in areas unsafe to divers such as with underwater foliage and

obstructions because the unit can become entangled. However, this search option

can be invaluable when retrieving bodies that are located using geophysical

methods such as side scan sonar and when depth conditions are not suited for

divers [1,4,9]. The ROVs are connected to a ship on the surface where an ROV pilot

can operate a number of acoustic and video imaging data collection systems [13].

Once the body is located with side scan sonar, an acoustic device is submersed near

the body as a reference for the ROV and the location is marked on the water surface

with a buoy [2,9]. The ROV operator will follow the line to the bottom surface and

the ROV operator can then use the acoustic target as a guide to the body location.

Once the body is located, the ROV arm will grasp and retrieve the body which is then

recovered at the water surface.

2.5. Cadaver dogs

While the use of search dogs began on land, a review of the literature by

Osterkamp [23] indicates that training and the use of dogs to locate drowned

victims was underway by the mid-1980s. Water search dogs are air scent dogs that

work with their nose in the air to pick up a human scent and seek its origin, and,

along with cadaver dogs, are the only search dogs trained to alert on human remains

[1]. A search dog is able to detect a submersed body by detecting scent and scent-

bearing materials shed from the body that rise through the water column to the

surface and enter the air [23]. The intensity of human scent in water searches is

affected by multiple factors that include water depth, air and water temperature,

length of submersion, experience of the handler, presence of currents and

thermoclines, and the weather [1,24]. In particular, it is not possible for a search dog

to pinpoint an exact location of a submerged body from a boat because of wind and

current patterns [1]. When the dog signals to the handler, a buoy should be used to

mark the location [24]. Handlers will then need to estimate the possible location of a

submerged body by considering the current and wind patterns and making multiple

passes over the area with a search dog, or multiple search dogs. Then a dive team or

an ROV is normally utilized to locate and retrieve the submerged body.

There are a number of recommendations provided when using dogs for a water

search. Search dogs used to search a water environment should be certified and

trained for searches on the water. While a search dog is normally deployed from a

boat to search for a submerged body, they can also perform a shoreline search.

Armstrong and Erskine [1] recommend that prior to searching a waterway for a

suspected drowned body such as a child that may have entered the water without

supervision, the local area should first be searched to make sure that the victim did

not walk away from the area. When a water search is performed, it is recommended

to choose a boat where the dog can get close to the water (e.g., inflatable Zodiac-

type and John-boats) because there is more scent at the surface, and the bow of the

boat needs to be large enough so the dog has room to move around [24]. Also, the

boat should move as slowly as possible, and an electric trolling motor is preferred

over a gasoline engine, as it does not produce fumes [24].

2.6. CHIRP sub-bottom profiler

A compressed high intensity radar pulse, also known as a CHIRP, is a sub-bottom

profiler used to map the sub-seabed and underwater archeological sites [25–30].

This system uses known and repeatable frequency-modulated (FM) acoustic pulses

with a desired frequency bandwidth to produce vertical seismic reflection cross-

sections of the sub-seabed according to their acoustic reflectivity [6,25,26]. The FM

source pulse consists of low frequencies that can penetrate into the sub-surface and

higher frequencies that provide high vertical resolution [31]. The FM signal is also

corrected for the source and receiver phase and amplitude responses [25]. Thus, the

signal-to-noise-ratio (SNR) is improved through matched filter processing that

correlates the reflection data with the transmitted pulse, producing improved SNR

and providing a beneficial trade-off between signal range and reduced image

resolution [31].

2.6.1. Benefits and limitations of using a CHIRP sub-bottom profiler

This is a valuable technology for forensic archeology because it can detect buried

structures and is the only geophysical surveying method that can detect buried

wooden artifacts [12]. While the application of CHIRP has not been reported in the

forensic case study literature, recent technological improvements in this

technology may be suited for forensic searches involving submerged evidence

and bodies. For example, 3-D data volumes can now be collected across a site using

CHIRP, and the processed 3-D volumes can provide increased horizontal resolution

over 2-D data, resulting in detection of small objects and imaging complex

geometries [25,28].

The CHIRP system deployment is similar to side scan sonar as the towfish or sub-

bottom profiling system is generally deployed behind a boat under the water. The

propagation of the acoustic waves is similar to seismic reflection as the acoustic

J.J. Schultz et al. / Forensic Science International 231 (2013) 306–316 309

waves also penetrate the subsurface [6]. The vertically propagating acoustic wave

will measure the acoustic impedance of materials based on their reflective nature

and record the different materials such as the individual layers of the sub-bottom

[6].

There are a number of disadvantages when using this technology for submerged

object searches. While depths of approximately 30 m can be achieved [26], shallow

water poses limitations for deploying chirp systems as depth may be too shallow to

operate the towfish [6,26]. The quality of the imagery can also be affected by the

sediment types [12,26]. While fine grained sediments such as silts and clays are

easier to penetrate, coarse sediments such as sand and gravels can be more difficult

to penetrate [12]. In addition, gas bubbles in the sediment or water body can also

affect the quality of the imagery [6,26]. For example, ‘‘acoustic blanking’ has been

described as faint or absent reflections resulting from gas absorption of acoustic

wave energy and that excessive acoustic blanking in the water column can be the

result of wake bubbles from the survey vessel’s propellers [28,32].

2.7. Ground penetrating radar

Ground-penetrating radar (GPR) has become a popular tool for forensic searches

involving graves and buried evidence by highlighting small areas across a much

larger survey area for follow-up invasive testing [4,33,34]. Since it is a non-invasive

tool, GPR can detect buried objects while preserving the context of the scene. More

recently, this technology is being used for forensic archeological contexts in water

environments [6,7]. While GPR identifies anomalies in the water column or bottom

surface, the radar frequencies can also penetrate the subsurface, thus it can be used

as a sub-bottom profiler to detect anomalies below the subsurface [6].

2.7.1. GPR methodology

Ground penetrating radar systems used for forensics in terrestrial environ-

ments are generally integrated into a cart with a built-in survey wheel. The

individual components include a monostatic antenna, a computer control unit,

and a monitor, or laptop, to view the GPR imagery, which can be configured

without a cart for other applications. The operation of a GPR unit begins by placing

the antenna on, or near the ground surface. Electromagnetic (EM) pulses of short

duration are transmitted into the ground from the transmitting portion of the

antenna, which are then reflected, refracted, and scattered off buried objects. The

returning waves are then captured at the ground surface with the receiving

portion of the antenna [4,33–35]. The GPR imagery can be viewed on the monitor

during the survey as a cross-sectional image of the subsurface that is referred to as

a reflection profile. Multiple refection profiles from a grid search can also be fused

together using GPR software to analyze a plan view of the grid at different depths.

When searching buried or submersed objects, the features on a reflection profile

will appear as a non-specific hyperbola and are called point reflections or

anomalies. However, the true shape of the features cannot be discerned from the

reflection profile, and the feature must be further investigated by divers or ROVs

with a video camera to determine the origin of the anomaly. As the EM wave

travels through the subsurface, features are detected because they will be

comprised of contrasting properties with the surrounding medium and will

produce a velocity change of the radar wave. Velocity, which is influenced by the

moisture content, is mainly controlled by the relative dielectric permittivity of the

soil, or burial medium [4,33–35]. For example, moisture content will vary between

soil horizons comprised of contrasting properties. This will produces changes in

relative dielectric permittivity at the interfaces of these horizons, resulting in

detection of theses horizons. Furthermore, a grave can be detected during a GPR

survey because there can be changes in relative dielectric permittivity with the

grave and surrounding soil. Contrasting properties within the grave environment

such as highly conductive metal objects and/or weapons, disruptions of soil

horizons, objects buried in the subsurface, or the buried or decomposing body will

be detected because of the relative dielectric permittivity changes compared to

the surrounding undisturbed soil [4,36–39].

Antenna size, which is generally based on the antenna center frequency, is a

consideration prior to performing a GPR survey. Two important variables when

selecting the appropriate antenna size are depth of investigation and vertical

resolution [4,33,37,40]. For example, a high frequency, 900 MHz antenna is

normally used for shallow depth investigations and increased horizontal resolution

of subsurface features. Conversely, a low frequency, 250 MHz antenna increases the

depth of investigation, but will result in decreased horizontal resolution. At the

same time, it is important to note that an increase in resolution from a high

frequency antenna may not result in an increased quality of the imagery because

increased false reflection features (clutter) may result in difficulty discriminating

forensic targets. Antennae of similar sizes to 500 and 250 MHz are most often used

for forensic applications in the terrestrial environment [36,40]. However, pre-

survey testing to determine the optimal antenna size for the particular soil in the

terrestrial environment should be performed, or the utilization of both size

antennae should be undertaken so both data sets can be assessed. When searching

for a large submerged object, Ruffell [7] determined that a 200 MHz antenna

provided the best trade-off for a water application involving detection of a sunken

jet ski.

While GPR is traditionally used over land or ice, this equipment can be deployed

from a small inflatable boat to survey water environments within the boat or by

attaching it to the boat [7]. Since GPR can also detect metal, it should not be used in a

metal boat if the antenna is mounted in the boat. Further, a borehole antenna can

also be employed into water because they are waterproofed [6]. Also, water

conditions should be assessed because waves or uneven surfaces can cause false

anomalies and water conditions should be assessed prior to performing the survey.

Suspending the antenna on a cable over water or waterproofing the antenna and

submersing it in the body of water can minimize the disturbances of turbulent

water [6]. However, while the antenna can be lowered into the water which reduces

the energy loss caused by deep water, the antenna and cable can be snagged on

underwater debris [6].

2.7.2. Benefits and limitations of using GPR

According to Parker et al. [6], who refer to GPR as water penetrating radar or

WPR, the main advantage of using GPR for water applications is it serves as a sub-

bottom profiler that can be used for a variety of fields including civil engineering,

sedimentation studies, and hydrological studies. Further, the small size of the

equipment is another advantage as it can be towed through, or above, shallow

waters that preclude the use of other geophysical tools such as CHIRP [6]. This tool

can also penetrate vegetation that can prevent the use of other techniques such as

side scan sonar, divers, or ROVs.

There are a number of limitations using GPR for water applications. The main

limitation includes not being able to use the equipment in saline environments

because the conductivity produces high attenuation and little penetration of the

GPR wave. Therefore, the equipment is limited to freshwater lakes, ponds, dams,

and upper sections of rivers [6]. A secondary problem in shallow water is coupling

the antenna to the water surface [6]. While a water proofed antenna placed directly

in the water results in a peak frequency change, if the antenna is not waterproofed

and therefore floated above the water in a boat, there will be a gap between the

water surface and the antenna resulting in attenuation of the radar signal. In

addition, GPR imagery is non-specific when detecting small targets such as bodies.

As a result, all of the noted reflections during surveys that are the size of a body, or

the specific evidence being searched for, would need to be physically inspected to

confirm whether or not the target was detected.

2.8. Side scan sonar

Side scan sonar was developed to survey and map the seafloor, although its

current applications have expanded beyond this limited purpose. In particular, side

scan sonar is now being used regularly as an underwater imaging method to locate

submerged archeological sites [41,42], the wreckage of airplanes and helicopters

[3], and downed watercraft [11]. Side scan sonar now has the resolution needed for

body detection [1] and is regularly utilized in forensic contexts to assist law

enforcement in the search for submerged bodies and forensic evidence [1,2,4,5,9].

According to Parker et al. [6], this equipment facilitates an ideal search method in

moderately deep waters (greater than a few meters) so there is sufficient depth to

tow the sonar behind a boat.

2.8.1. Side-scan sonar methodology

Side scan sonar uses a wide-angle pulse of sound frequencies at right angles to

the tract of the boat to detect anomalies on the sea floor [43]. The equipment

consists of a projector that emits signals and a hydrophone that receives signals

within a towfish, a tow cable, and an electric recording device such as a laptop or

waterproof control unit (Fig. 1). In monostatic sonar systems, the projector and

hydrophone are combined into one unit, collectively called transducers, that

emit acoustic signals for 5–1000 ms. When the voltage stops, the transducers

receive the returning echoes. Once the transducers are reset, they emit sound

again, and the cycle continues [1]. The projector converts electrical signals into

pressure waves, which propagate through the water and reflect off of raised

objects on the bottom surface back to the hydrophone receiver [43,44]. The

strength of the frequency returning to the hydrophone is interpreted and

translated into electrical signals, which return to the monitor on the boat via a

cable. The towfish is towed by a cable from the boat (Fig. 2), and therefore, the

speed of the boat must account for the towfish so that the towfish is level during

the sonar process. Sonar should not be operated during a turn, as this would

distort the sonar image [45]. The operator also controls the depth of the towfish,

since the towfish is most effective when it is as close to the bottom as possible.

This underwater imaging method does not calculate depth; rather, the intensity

of the information from the returning sound that is scattered back to the towfish

is displayed [12].

The frequency of the towfish is a consideration for forensic searches as frequency

affects the distance the acoustic signals can travel as well as the resolution of the

images. Lower frequencies can travel further distances, but higher frequencies have

increased resolution [46]. Resolution is defined as the ability to discern between

two distinct objects [47]. Therefore, higher frequencies are more likely to discern

between two closely spaced objects, but these frequencies will also provide

additional clutter due to increased sensitivity. While an operating frequency of at

least 400 kHz or higher is recommended for body searches [1], higher frequency

towfish used for forensic applications are now available with dual frequencies that

allow the operator to choose between 900 and 1800 kHz.

Fig. 1. OCSO Marine Unit side-scan sonar equipment: (a) waterproof control unit and monitor; (b) towfish, cable and winch; (c) GPS receiver. The sonar equipment is deployed

from the front (bow) of the pontoon boat (d).

J.J. Schultz et al. / Forensic Science International 231 (2013) 306–316310

2.8.2. Side scan sonar imagery features

The acoustic signals transmitted from the towfish are converted to electrical

signals and displayed on a monitor in real-time. The monitor can be adjusted to

different color schemes based on the operator preference, but the color scheme

most often used is a bronze color scheme that produces a brighter bronze hue for

reflective objects. The image resulting from a side scan sonar survey has several

distinct features (Figs. 3 and 4). Recognizing these features allows the sonar

operator to better interpret the record. Different materials will have different

reflective properties, or back scatter of the signal, influencing whether items will be

recorded by the side-scan sonar. For example, materials with higher reflection

coefficients, and a rougher appearance, such as rock and metals, provide stronger

return echoes and produce stronger reflective acoustic signals than finer grained

sediments like sand [1,6,12]. The contrast or reflection coefficients allow objects to

stand-out against low reflection materials, making it easier to locate a body on a flat

mud bottom [1]. In this instance, the raised body will be easily detected as it

Fig. 2. Illustration showing how side-scan sonar detects submerged bodies.

provides a strong return signal against the flat bottom because the flat bottom does

not produce a good output on the display [6].

Fish and Carr [43] discuss the various features of the sonar image (Fig. 3). The

path of the towfish is marked by the trigger pulse is the first return echo directly

under the towfish. The next return is the first bottom return. The distance between

the trigger pulse and the first bottom return should be minimized for the best

possible picture, as features in this area will not be visible. The area between the

trigger pulse and the first bottom return is the water column. Features may appear

in the water column, but these are typically clutter or noise caused by reflections off

of the water surface. In addition, the acoustic signals can be transmitted out of the

left side of the towfish, the right side of the towfish or both sides of the towfish.

Figs. 3 and 4 illustrate an image in which the acoustic signals are propagated out of

both sides of the towfish. The trigger pulse will appear on the opposite side of the

direction in which the acoustic signals are projected. Therefore, if the signals are

transmitted out of the left side of the towfish, the trigger pulse will appear on the

right side of the sonar image. The width of the sonar image is determined by the

range scale, or swath width of the towfish. For example, a towfish can have fixed

adjustment settings that project the acoustic signals a distance of 10 m, 20 m or

30 m on either side of the towfish, or only one side of the towfish. Atherton [1]

recommends that the range scale should be adjusted for the smallest dimension of

an adult body such as a width of the trunk, while a search for a child would require a

shorter range scale. For instance, an adult sized body on a low acoustic reflective

surface should be detected using a range scale of no more than 25 m (82 ft). At the

same time, it is recommended to maintain a 50% overlap between transects [1].

Detected features within the sonar image will contrast with the bottom surface

based on their reflectivity. Also, a shadow will appear to the opposite side of the

object from the towfish (Fig. 4) which can be the most important imagery feature

recorded because it provide a three-dimensional quality to a two-dimensional

survey [12]. The shadow detail compliments the echo (backscattering) information

and may provide more information than the shape of the target. For certain angles,

the shadow will better illustrate the morphology of the feature than the feature

itself and can assist in differentiating features from noise or feedback [46]. Often,

the feature itself may be obscured, but the shadow will closely resemble the object

and can provide more information on the morphological characteristics of the

object than the image of the feature itself. For example, an object such as a bicycle,

may present as only a line for a feature if the towfish runs parallel to it. However, the

shadow can reflect the image of the bicycle as the acoustic signals go through the

spaces between the frame and the spokes [1]. The shadow also differentiates

features from noise or feedback interference. Noise or feedback may resemble a

feature, but only a feature will have a shadow, which indicates the vertical nature of

the object [46]. Other types of interference affecting the image quality originate

Fig. 3. Side scan sonar image with labeled features collected with 1800 kHz

frequency and acoustic signals projected out both sides of the towfish.

Fig. 4. Side scan sonar image of a sunken boat (approximately 4.5 m long and 2.0 m

wide) collected with 1800 kHz frequency and acoustic signals projected out both

sides of the towfish.

Fig. 5. Florida map with inset showing lake locatio

J.J. Schultz et al. / Forensic Science International 231 (2013) 306–316 311

from seismic instruments, dense particle suspension in the water column, and

ultrasonic waves created by passing ships [45]. Additionally, water with waves of

sufficient height or wave action in shallow water can cause the boat to pitch and roll

affecting the stability of the towfish and producing image distortion [1].

2.8.3. Operation of side scan sonar

Since acquiring the side-scan sonar system in 2007, the OCSO Marine Unit has

utilized side scan sonar for a variety of purposes. A pontoon boat is normally used to

employ the sonar (Fig. 1d), although a John-boat can be used in smaller waterways.

The system has enabled the Marine Unit to locate water accident victims, search a

submersed airplane crash site, search for large evidence such as stolen cars, and

scan lakes for possible dangerous obstacles. These searches are conducted on a

variety of waterways in central Florida, including lakes, retention ponds, and canals.

Additionally, the OCSO Marine Unit has been called to assist other jurisdictions in

the central Florida. While the OCSO Marine Unit was the second jurisdiction in

central Florida to utilize this methodology as part of their water search protocol,

multiple sheriff offices in central Florida (Lake, Brevard, Martin, and Osceola

counties) as well as the Tampa Police Department, have recently obtained side scan

sonar equipment. This technology has become a valuable tool for law enforcement

in the central Florida region when searching for submerged bodies and evidence

because of the high number of waterways throughout this area.

For proper operation of the side scan sonar, OCSO Marine Unit generally employs

a three-man team. Typical operation requires a boat driver, a sonar operator and a

ns for case studies in Orange County, FL, U.S.

Fig. 6. Aerial image of the south side of Lake Underhill showing the approximate locations of Search Area 1, Search Area 2, and the detected body (white arrow pointing to body

outline).

Fig. 7. Side scan sonar image showing debris detected on the bottom of Lake

Underhill in Search Area 1 near the southern boundary of the SR 408 Bridge. Image

collected with 900 kHz frequency and acoustic signals projected out the left side of

the towfish.

J.J. Schultz et al. / Forensic Science International 231 (2013) 306–316312

deckhand. The boat driver is responsible for maintaining a consistent speed of no

more than 3.5 knots, although the slower the boat is operated, the better quality of

the imagery. The boat driver also works with the sonar operator to ensure that the

search area is completely covered. Since the towfish is towed by a cable from the

boat, the speed of the boat must account for the towfish so that it is level during the

sonar process. The sonar operator is responsible for marking any anomalies on the

monitor for further investigation and ensuring the search area is completely

covered. The deckhand is responsible for deploying and retrieving the towfish, as

well as deploying buoys. If anomalies need to be investigated, the sonar operator

directs the deck hand to mark the location with a surface buoy so that divers can

further investigate the feature, and recover if necessary.

When performing searches, the search team should begin at the last known

location on the water. A GPS receiver is attached to the sonar unit allowing the boat

driver to monitor the path of the sonar and to ensure that the boat is traveling in

straight and parallel transect lines to cover the entire search area. For a sonar search,

the area should be marked with a surface buoy at each corner, and the boat should

turn outside of the search area. Also, weather conditions, such as strong winds, can

affect the transect headings, which should be accounted for by the boat driver.

2.8.4. Benefits of side scan sonar

Side scan sonar is becoming more commonly used as an initial search method in

forensic contexts to locate possible features such as bodies, evidence, or watercraft

in both fresh- and saltwater. There are numerous advantages to using side-scan

sonar for a submersed evidence or body search. In particular the high quality of the

image provides a real-time snapshot of the bottom surface. This geophysical search

method requires less manpower and less time to perform detailed searches

compared to other traditional search methods such as dive teams and cadaver dogs.

This is a major advantage because recovery can occur on the same day before

significant taphonomic factors can affect the body and evidence. Moreover, side scan

sonar is not affected by murky or black water, and can be used to perform searches

during inclement weather with low visibility and after nightfall. Side scan sonar can

also be employed when the risks are too great to utilize divers. However, a number of

factors can influence the success of a search with side-scan sonar. Quinn et al. [48]

found that a geophysical survey, such as one with side scan sonar, provides a quick and

effective survey method, although it is dependent on the experience of the operator,

the navigation by the driver, and the quality of the image.

3. Case studies

While there are a several forensic examples employing sidescan sonar to locate submerged bodies [1,2,4,9], it is important tocontinually present forensic cases studies to understand thelimitations and advantages of this method for various types ofwaterways. Two successful OCSO Marine Unit cases in OrangeCounty, Florida (Fig. 5) are presented to demonstrate the use of sidescan sonar for locating submerged bodies.

3.1. Equipment

A Centurion Sea Scan dual frequency side scan sonar towfish isemployed by the OCSO Marine Unit. This sonar system received thesecond highest overall score from U.S. Department of HomelandSecurity’s System Assessment and Validation for EmergencyResponders [49] based on its affordability, ease of use, portability,easy system setup, resilient equipment, and readable screen. The

Fig. 8. Side scan sonar image showing detected body and shadow formation on the bottom of Lake Underhill (black box) in Search Area 2. Image collected with 1800 kHz

frequency and acoustic signals projected out the left side of the towfish. Note zoomed image (inset) of body with shadow formation on right side.

J.J. Schultz et al. / Forensic Science International 231 (2013) 306–316 313

towfish can be operated at either 900 or 1800 kHz, and a pontoonboat was utilized to tow the side scan sonar (Fig. 1). The towfishwas towed from the front of the boat, and a GPS unit was connectedto the sonar control unit to establish grid coordinates during thesearch.

Fig. 9. Aerial image of the south side of Lake Lawne showing the approximate lo

3.2. Case study one

During May 2010, the Orlando Fire Department requested theservices of the OCSO Marine Unit for a body recovery on LakeUnderhill (Fig. 6) after a boating accident. The sidescan sonar

cation of the search area and body (white arrow pointing to body outline).

Fig. 10. Side scan sonar image showing detected body as an obscure shape on the bottom of Lake Lawne (white box) in the search area adjacent to a depression. The gain was

poorly adjusted due to the fluctuating depth, which obscured the shape of the body. Image collected with 1800 kHz frequency and acoustic signals projected out the right side

of the towfish. Note zoomed image (inset) of body and linear projection on the right side of the body that shows one arm.

J.J. Schultz et al. / Forensic Science International 231 (2013) 306–316314

search began three hours after the boating accident. The meandepth of the lake was 4.27 m with a maximum depth of 8.84 m. Thelake contained a relatively flat, clear, silt and sand bottom,although submerged grass was located near the dock (easternshoreline near bridge) away from the sonar search. Witnessstatements pinpointed a specific location (Fig. 6, Area 1) closer tothe bridge that was the primary area of the search (Fig. 6). Also,there was debris in the initial search area (Fig. 6, Area 1) related tothe construction of the bridge for State Road 408 that waspositioned in a west to east direction somewhat centered over thelake.

There was a possibility for Area 1 to present difficulty detectingthe body because of submerged debris related to the bridgeconstruction (Fig. 7). However, after two hours, the OCSO Marine

Fig. 11. Side scan sonar image showing poorly defined outline of the body shape on the

frequency and acoustic signals projected out the right side of the towfish. Note zoome

Unit’s search completed Area 1, and the body had not been located.The Marine Unit then expanded their search further south (Fig. 6,Area 2), which was beyond the location of the witness statements(Fig. 6). Additionally, the sun set during the search, but continuedafter dark. Within an hour of searching Area 2, the body waslocated in a relatively clear and flat area on the bottom of the lake(Fig. 8). The clear, flat area of the lake bed provided optimalconditions for detecting the body with the sonar. The location wasmarked with a surface buoy so the body could be retrieved bydivers. This case illustrates the ‘‘almost-perfect’’ scenario for sonarsince the night-time search prevented divers from searching, andthe silt and sand bottom provided an easily discernible image ofthe submerged body. Additionally, the search was able to expandbeyond the area specified by witnesses with relative ease and an

bottom of Lake Lawne (black box) in Search Area. Image collected with 1800 kHz

d image (inset) of body with shadow formation on right side due to the arm.

J.J. Schultz et al. / Forensic Science International 231 (2013) 306–316 315

expanded search area did not drastically affect the search time,which was approximately three hours.

3.3. Case study two

The second case study describes a successful search that poseddifficulties imaging a clear outline of a submersed body. DuringFebruary 2011, the OCSO Marine Unit responded to a jet skiaccident on Lake Lawne (Fig. 9). In this case, the victim fell off of ajet ski without a life preserver. The OCSO Marine Unit respondedimmediately and began the search at 5:30 pm. However, it was notpossible to deploy divers initially because the sun set an hour intothe search. Witness accounts again provided a specific location, butthe lake bottom had numerous holes that inhibited the sonarsearch. At the same time, this shallow lake has an average depth of1.83 m and a maximum depth of 7.32 m, with the depth rapidlyfluctuating. The undulating surface created challenges for thesonar operator since the towfish depth had to be continuallyadjusted. With each depth adjustment, the sonar operator had toensure that the towfish was not positioned too low to becomeentangled on the lake bottom, and the operator had to adjust thegain of the image for optimum image quality. If the gain is set toohigh or too low, it could inhibit the operator from visualizing thetarget. The combination of nighttime search, shallow lake bed withfrequent fluctuations in depth, and the continuous gain adjust-ments required numerous operators as the operator eyes wouldbecome fatigued quickly.

In this case, contrasted to the previous one, the OCSO MarineUnit was able to locate the submerged body in the area identifiedby eyewitnesses. However, the body was located on the edge of adepression and the shape and shadow of the body were obscuredby the depression, creating additional imagery challenges for thesonar operator. The sonar operator initially interpreted an oddshape as a possible target, and the size of the target suggested theymay have located the body (Fig. 10), but the gain setting and thedepression in close proximity masked the distinctive shadow. Theythen investigated the anomaly by collecting data with better gainadjustment. The additional data collection resulted in a humanbody shape with an associated shadow formation on the sonarimagery (Fig. 11), which was confirmed as a body by the deployeddivers. The body was recovered at 9 p.m. – 3.5 h after the searchbegan.

4. Discussion and conclusions

Successful searches for submersed bodies and objects generallyinvolve the integration of multiple search methods. While the useof dive teams, ROVs, and water search dogs have been commonmethods employed for submerged object and body searches,integrating winthroping methods to determine access points intobodies of water can be important when beginning the search forsubmerged objects. Also, the application of geophysical methodshas been gaining popularity. For example, side scan sonar hasbecome a popular geophysical option for law enforcement andsearch and rescue applications [1,2,4,9], as it can be integratedwith other methods as part of the protocol for object searches. Inparticular, submersed bodies are located more rapidly than onlyutilizing divers, and search areas can be cleared quicker usinggeophysical technologies so personnel and resources can beutilized more efficiently. At the same time, if time permits,multiple geophysical methods can be used for the same forensicobject search.

As was demonstrated with the case studies, a major benefit ofusing side scan sonar for water recoveries is a decreased timeinterval to locate submerged bodies and also a decrease in thesubmerged time of divers. In particular, recovering bodies soon

after being submersed reduces the taphonomic effects to the bodyand potential evidence. Additionally, side scan sonar allows waterrecovery to continue despite inclement conditions, such as poorvisibility or nighttime. The OCSO Marine Unit was called to each ofthe previous case studies in the late afternoon, which would havelimited the amount of time divers could search for the body.However, since side scan sonar can be employed when thevisibility is poor for water and surface conditions, it can be utilizedwhen divers cannot, resulting in faster body recoveries. Therefore,since the OCSO Marine Unit could employ the side scan sonar afterdark, the bodies were recovered in each case within 3 h and 3.5 h,respectively, whereas if divers were utilized instead of sonar, thesearch would have had to stop and continue the next day.

It is important to not only understand the advantages of thevarious water search methods for different types of targets, butalso to understand the limitations of these methods. At the sametime, it is important to have knowledge of the water body size,depth of investigation, and the sub-bottom sediment and geology[6]. For example, in areas of rapidly changing bottom elevation,there may not be adequate coverage for side scan sonar if thetowfish is positioned too high in the water column [2]. The lake bedin the second case study contained a multitude of depth changesrelated to depressions in the lake bottom. Since the side scan sonaroperator has to adjust the gain of the image each time the operatorchanges the depth of the towfish, locating objects or bodies arounddepressions is more difficult and requires a more experiencedoperator. Additionally, debris on the water bottom and aquaticvegetation can also affect the use of sonar. Areas with thickvegetation will reflect the sound waves back to the sonar withoutpenetrating the vegetation. If the extent of the aquatic vegetationlimits a dive team or side scan sonar search, water search dogs for abody search or possibly GPR would be better options in thisenvironment. In the first case study, there was construction debrisleft over from the construction of a bridge over the lake (Fig. 7).While the body was not located within the debris, extensive debrison the bottom could mask and prevent the detection of a bodyusing both side scan sonar and GPR, and also inhibit diver recoveryas well, as divers lines could easily become entangled in the debris.In this scenario, water search dogs may be a better option to use asthe initial search method.

While GPR may work in submersed environments that inhibitside scan sonar, it is important to note that there can be sitevariables that inhibit the use of GPR such as a saline waterenvironment. Another site variable that can limit side scan sonaruse is buried targets. If for some reason the submersed body isthought to be buried, GPR and CHIRP would be better options touse for a geophysical search as side scan sonar cannot detect buriedtargets [6]. Furthermore, if the target in question is a small metalweapon, then GPR or divers with a hand-held metal detector maybe the best options.

When searching for submerged objects, investigators will havethe greatest degree of success when integrating multiple methodsand utilizing a search protocol based on the type of water body, theenvironmental conditions of the water body and the specific typeof target being searched for. Simultaneously, the application ofgeophysical search methods is an important aspect and mayinvolve the integration of more than one geophysical tool.Furthermore, with improvements of geophysical technologiesfor object detection, more advanced technologies will beeventually incorporated into the search protocol for submersedobjects. For example, there are a variety of forward-looking sonar(FLS) designs, including those that are operated by an AUV, that arecurrently used in mine hunting operations and obstacle and terraindetection [50]. More recently, the Echoscope 3-D sonar technologythat was developed by CodaOctopus Products Ltd. uses a narrowfan of acoustic beams to provide a real-time 3-D image of the

J.J. Schultz et al. / Forensic Science International 231 (2013) 306–316316

underwater landscape that will accurately measure the position ofdetected underwater objects relative to the ship [51]. While thistechnology can be used for numerous underwater applications,incredibly, moving objects such as divers can be captured because12 frames/pings per second are captured and displayed in a formatsimilar to video [51]. Thus far, there are no case studies in theforensic literature discussing the use of these newer geophysicaltechnologies for forensic and search and rescue applications.However, it is only a matter of time until real-time 3-D sonar isused for submerged object searches.

Acknowledgements

We would like to thank the team members of the OCSO MarineUnit and Dive Team for their assistance with the case studies. Also,thanks to the anonymous reviewers and Brittany Walter forproviding constructive comments that strengthened this paper.

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