Though border concerns have existed since the conception of the United States, post September 11, 2001, these concerns grew markedly. Fences, walls and guard posts along the U.S. Mexico border were established or fortified. More regular patrols of the borderline by Homeland Security agents were initiated. These infrastructure and personnel investments are expensive to initiate and maintain and are still ineffective at complete surveillance of the 3145-km border; approximately 250,000 people try to cross the border illegally each year who have stepped into action. Aside from the human rights violations that such forms of surveillance pose to groups seeking to cross the border, these homeland security activities are also threats to the environment. Environmentalists worry that the new roads, fences and facilities created to accommodate these new forms of surveillance are degrading fragile desert landscapes, ripping up vegetation, compacting soil and threatening wildlife movements . Finally, these operations seriously threaten precious and irreplaceable archeological sites located along the nations’ borders. Although the use of remote sensing cannot address the human rights violations, geopolitical tensions or cultural and ethical problems posed by current forms of border surveillance, it does offer ways to make homeland security efforts more efficient at recognizing extra-legal migrations, while also potentially lessening the impact of current efforts on the environment and cultural heritage sites. Using aerial and satellite images, remote sensing can allow Homeland Security officers to target their surveillance and enforcement efforts by revealing where smuggling or migrations are taking place by displaying habitual paths through the desert. They may also allow law enforcement agents to stay out of harms’ way during reconnaissance missions. Further, with increasingly advanced technology, 4×4 flood tray remote sensors affixed to light aircraft provide almost real-time detection of human movement across the landscape. Targeted efforts and fewer law enforcement vehicles and patrols for surveillance may lessen the impact of border security on local ecologies.

Remotely detecting smuggling or extra-legal migrations is more difficult than detecting the growth of drug crops, because these illicit activities are not static; people and goods can move across a landscape in a matter of hours. Thus, the adoption of these techniques is still in progress. To try to detect where drug, human and arms smugglers were traveling through the landscape, Kaiser and others used ADAR 5500 mounted on a helicopter to try to detect trails crossing the desert border along the southern limit of the United States. Cao and others conducted a similar study in 2007 [87]. Coulter and others used a Canon EOS 5D Mark II camera system fixed on a light aircraft to detect the active movement of people through the landscape in near-real time. In all of the terrestrial cases we reviewed , it is assumed that the movement of any people through this landscape is linked with smuggling or extra-legal migrations, since remote sensors are unable to detect the intentions or identities of these people. This, in and of itself, is a problematic assumption given that these areas have traditionally been used by indigenous groups, homesteaders and cattlemen for generations. In situ interactions with people in these areas would facilitate the detection of various people’s identities and intentions. Problematic at a different level, remote sensing would be unable to detect smuggling operations that occur via trucks or through tunnels under the U.S.-Mexico border, which may be equipped with electricity and rail systems . The U.S.-Mexico border is not the only place where remotely sensed surveillance for crimes and criminals is taking place, however. As Zhao shows, many countries in Europe, Asia and North America are working to develop ship surveillance systems to detect ships that may be used for extra-legal migration, illegal fishing, piracy and smuggling along maritime borders . These surveillance systems integrate Synthetic Aperture Radar satellite data with automatic identification systems that are ship, land and space-based. Although we did not find any studies that chronicled the active detection of crime , there exists a plethora of studies that present theoretical or retrospective case studies of how this might take place.

These studies tested the use of TerraSAR-X, TanDEM-X, RapidEye, RADARSAT, Envisat-ASAR, Cosmo-Skymed, MODIS and ALOS images to detect the presence of ships in the Mediterranean, the North Sea, the Gulf of Aden, the Campos Basin, the English Channel, the Port of Halifax, the Bosporus, the Ionian Sea, the Southern Ocean and the Strait of Italy. There also exists a fairly extensive literature that deals with the active detection of oil spills , as well as illicit drift-net fishing . Both of these topics fall outside the realm of our analysis, however. While these studies differ from terrestrial studies of human and drug trafficking in that they acknowledge that ships may have many uses that are not nefarious, these studies do seek to survey some of the most vast and unmanned areas on the planet. Differentiating between legitimate ship users and potential pirates or smugglers presents a challenge. Some scholars have proposed methods of differentiating “abnormal behavior” from standard shipping procedures to identify piracy in action. These studies consistently must deal with false alarms in their detection algorithms caused by oceanographic or meteorological phenomena and bathymetry—underwater banks and azimuth ambiguity. Any credible remote sensing project should assess the accuracy of its results, and particularly those used in the active detection of crime. In these projects, accuracy or validity can be thought of as the “correctness” of the resulting map or classification product . The means by which accuracy assessments have been carried out have changed over time, starting as an afterthought and progressing to a well-defined and necessary component of remote sensing analyses . These “first order” accuracy assessment protocols ideally include well-distributed independent samples from the ground or a data source of higher accuracy , development of error matrix reporting of the overall error, errors of omission and commission per land cover class and the kappa statistic. Although remote sensing analysts attempting to detect crimes acknowledge that ground-referenced data is the gold standard for accuracy assessment, publicly available gray literature and peer reviewed papers agree that this method is not always feasible, due to security concerns, rugged and remote terrain and funding limitations. Eleven of the 58 studies on drug production that we reviewed reported that their accuracy assessments were limited due to insecurity issues on the ground. Of the same group, eight reported that no accuracy assessments were possible because of insecurity . The security concerns addressed in these reports are very serious. For example, a member of a ground survey crew in Afghanistan was killed while collecting data on cannabis production in 2009. Ground validation of extra-legal migrations in U.S. borderlands was also limited by security concerns and dense vegetation. In order to avoid the issues presented by potentially dangerous and/or expensive field missions for ground reference data collection, analysts seeking to assess the accuracy of their illicit drug identification have come up with alternative methods . For example, Chuinsiri et al. used large-scale aerial photographs collected at the same time as the satellite data for accuracy assessment instead of gathering ground reference data. Unfortunately, these aerial surveys may not be as effective as ground surveys. For example, in a similar study, aerial surveys were often unable to detect shade-grown coca. In other cases, bad weather delayed the collection of data from aircraft, putting the utility of the data collected for accuracy assessment into question. Further, one UNODC report notes that even over-flights were too dangerous in certain regions, thus limiting the accuracy assessment within those areas. In cases where ground or aerial validations proved unfeasible, analysts sought other means of performing accuracy assessments of their detection of illicit crops. In some cases , “surrogate” ground-reference data were produced using the visual interpretation of two satellite images using poppy reflectance, disappearance of the vegetation in the second image , apparent fields surrounded by natural vegetation, distance to populated spaces and accessibility. UNODC used a quality control mechanism that involved each analyst’s work being checked by two other experts and then cross-validating first and second dated photographs rather than using ground validation data.

Wang used UNODC and the Islamic Republic of Afghanistan Ministry of Counter Narcotics’ surveys from the same time period as satellite data were collected to calculate the accuracy of his classification of opium crops. Where no survey data were available, Wang used coarsely constructed opium maps. Surprisingly, hydroponic tray over thirty-six percent of the drug production studies reviewed did not mention accuracy assessments in any way . Those that did discuss validation often did so in limited ways. In one study, analysts did not update the previous years’ accuracy assessment, assuming that a similar level of accuracy could be considered for the year at hand. Similarly, in all three of the studies of illicit human movements in the landscape that we reviewed, accuracy assessments either were not performed, or the methods for assessment were not mentioned or clearly discussed. For example, despite the fact that Coulter and others have a table assessing the accuracy of their detections of trails, they do not describe how they calculated these percentages. The lack of discussion of accuracy assessments in drug and human-movement studies is surprising given the potentially serious impacts these reports may have on local communities and ecologies. Because this is a review paper, we were unable to independently research the potentially harmful ecological and social impacts that a lack of validation may have had, but we believe it is important to raise the point that studies with such important real-world implications should be validated; and many are not. Most of the retrospective and theoretical marine case studies relied on ship-specific automatic identification systems data to validate the remote sensing of ships. Posada and others point out three problems with AIS to validate remote sensing. First, AIS equipment is often misused by its operators, resulting in the wrong ship ID numbers being attached to a given vessel, potentially misrepresenting the type of ship that is on the water. Second, AIS messages “regularly contain errors ”, leading to confusion in ship tracking. Third, AIS do not report ship position rapidly, thus, if there is a significant time gap between when SAR data were collected and when AIS data were reported, the ship may have moved a significant distance, making validation very difficult. Beyond these three limitations, Lehner and others point out that smaller vessels may not have AIS and may also be more difficult to differentiate from false-alarms, like breaking waves. We posit that few ships intent on criminal activity would have AIS either. Finally, Paes and others note that the Earth’s curvature and meteorological influences on data transmission leads to instances where vessels far from the coast are not present in the AIS databases. To get around some of these issues, some scholars used maritime patrol aircraft to survey blank areas, had analysts do manual inspection of images or did on-the-ground validations of ships. All of these techniques are difficult, time consuming and expensive to enact, thus making it likely that validation of actively identified marine crimes will follow similar trends as terrestrial drug production or smuggling. Aside from the more refined remote sensing techniques we mention above, law enforcement and government officials have leveraged the power of freely available remotely sensed products, like Google Earth, to detect crime. Although, to date, there is a limited discussion of the use of Google Earth to detect crime in the academic literature, it is widely discussed in the popular press . These discussions note that Google Earth is being deployed by law enforcement officers, government employees, scientists and even private citizens to actively detect crimes in progress around the world. For example, a Swiss police department “stumbled across a large marijuana plantation while using Google Earth”. Aside from international agencies and law enforcement departments, researchers, like Anthony Silvaggio, an environmental sociologist at Humboldt State University, have sought to point out where large-scale, unregulated industrial marijuana grow sites are occurring in Humboldt county, California, including in national forests. Amateur searchers have also started seeking out and identifying marijuana growing using Google Earth . Google Earth’s use for crime investigation does not stop at drug production, however. In Greece, Italy, Argentina, India and the United States, Google Earth has been used by government officials to identify homes that have violated building codes, built swimming pools without permits and to compare declared home values with actual existing structures.