[The following is the text of an informative article written by a Leiden University (Netherlands) colleague, Sabrina Rewald, and me. It was published on July 1, 2024, in the European Journal of International Law as part of its EJIL: Talk! series. Various parts of article have helpful hyperlinks (not reproduced below) and so you may want to read the article in EJIL: Talk! at https://www.ejiltalk.org/the-satellite-era-how-earth-observation-data-is-being-mobilized-as-potential-digital-evidence/]
Public monitoring of ongoing conflicts, for example in Gaza, Ukraine, and Sudan, demonstrate the extent to which both human rights defenders and journalists increasingly rely upon earth observation data (EOD) to ascertain and substantiate facts on the ground. EOD is inclusive of data collected by satellites—such as satellite images, radar information, and other remote sensing data—as well as aerial images collected by aircraft or drones. As this blog will discuss, EOD can be a highly probative form of digital information. EOD can objectively depict static and transient features of geographical areas of interest and activities contained therein, which makes it particularly useful as potential evidence of international crimes. Combined with its exponentially increasing availability and quality, the past decade has seen an increasing reliance on EOD as evidence. As a result, some scholars have called for the establishment of standards regarding satellite data and its use potential as evidence. It is evident that we have entered a ‘satellite era’ of international law, wherein EOD has gained a strong foothold.
The first use of EOD before an international accountability mechanism was in 1986 at the International Court of Justice. It was not until the late 1990s that EOD was used as evidence in an international criminal setting, at the International Criminal Tribunal for the former Yugoslavia. A watershed moment in digital evidence, aerial imagery collected by American U2 reconnaissance planes was instrumental in depicting the Srebrenica massacre of more than 8,000 Bosnian-Muslim men and boys in July 1995. The images, which depicted movement of earth, were employed as part of a comprehensive forensic investigation that proved the existence of numerous mass graves.
Satellite imagery has also been used by several human rights fact-finding missions. For example, the Independent International Commission of Inquiry on Ukraine used satellite images to corroborate the widespread destruction of residential areas in Mariupol when the Commission was unable to physically access the city. Indeed, this ‘remote’ element of remote sensing data is a key benefit highlighted by scholars, namely that of gaining access to ground-based visuals and data without stepping foot in a conflict zone. Commercial EOD are also becoming increasingly sophisticated, with certain companies offering ultra-high resolution earth observation images and technology that can see through any atmospheric conditions.
Additionally, EOD can offer information that may not be available from ground level. For example, when high-resolution satellite images of Gaza were temporarily embargoed by some commercial satellite companies following the 2023 resurgence of the Israel-Hamas conflict, the Decentralised Damage Mapping Group turned to open-source satellite radar data for a multi-dimensional portrayal of the extent of destruction in Gaza. A conflict can also be heat-tracked via EOD: A report by Bellingcat describes how independent OSINT mappers employed an open-source NASA fire-management tool to remotely track the trajectory of the conflict in Ukraine in 2022. The report asserts this technique can be particularly useful to track conflict activity with small digital footprints, using the civil war in Ethiopia as an example.
Earth observations can take different postures when monitoring a conflict area, each posture serving a different purpose. The detection posture is used by analysts to predict whether threats to civilians exist, for example by identifying the movement of troops and related infrastructure. During the Dutch prosecution of the 2014 MH17 flight downing in eastern Ukraine, satellite images were used to show the movement of military equipment from one region to another. These locations were then linked to ground-based imagery showing smoke trails attributed to the firing of BUK missiles from ground launchers. During the early stages of conflict, a deterrence posture can be utilized, which is designed to warn civilians of pending attacks. Post-atrocity, analysts can assume a documentation posture by gathering visual evidence such as images of mass graves, burned structures, and the detritus of conflict. More recently, this level of documentation has been used as evidence before the ICC to show before and after images of mausoleums and mosques destroyed by criminal actions (Al Mahdi, Al Hassan—judgment expected 26 June 2024) through the use of interactive 360º visual representations linked to EOD.
Accountability mechanisms take advantage of two key types of evidence satellite imagery offers. First, the identification of observable objects at a given point in time allows for a macro analysis of locations, including the depiction of permanent or semi-permanent landform and architectural features, as well as transitory features such as vehicles, equipment, and people. Second, the documentation of observable changes in the position and condition of those objects over time may serve as independent evidence and may also corroborate ground-based accounts of atrocity crime activity. Satellite imagery thereby allows viewers a reconnaissance of both the past and present.
Critical issues that apply to satellite images are authentication, reliability, and interpretation. The party that tenders EOD before an accountability mechanism such as the ICC has an obligation to authenticate it, which means leading evidence sufficient to support a finding that the data in question is that which its proponent claims it to be. Authentication therefore describes a positive action, not a state of being. Authentication of satellite images requires that counsel establish the depicted location so that it can be spatially linked to a relevant event. Similarly, the date the image was recorded, and in some cases the time, are essential components of authentication as they serve to establish a temporal link between the images and the issues raised by the indictment.
Depending upon the available evidence, authentication can be addressed in different ways. First, images may be authenticated internally by proving the technical soundness of their metadata and visible content. Second, authentication may be proven externally by evaluating other reliable evidence, including viva voce evidence, which can corroborate image content. At times, a combination of both methods may be used. Third, multiple sources may be able to cross reference and circumstantially corroborate temporal and spatial narratives reflected in the images that might otherwise suffer from lack of authentication. This approach may not directly authenticate imagery but can provide sufficient contextual confirmation to indirectly achieve that result. Failure to follow any of these methods in support of authentication should result in exclusion of the tendered evidence.
Once authenticated, remote sensing images must also be shown to be reliable for the purpose tendered. This involves an assessment of the clarity and resolution of the images vis a vis the purpose for which the images are being used. There are no prescribed legal rules that set out minimum technical specifications for EOD. An image would be considered to be of optimal reliability if it displayed sufficient clarity and resolution to allow for informed content interpretation by viewers, but even suboptimal images may be adequate when being used to examine an event at a macro level, looking for things like geography, buildings, vehicles, and the movement of people, provided they offered a threshold level of clarity and resolution to achieve those objectives. Conversely, the same images may be wholly unsuitable and unreliable when looking for minute geographical, building, or vehicle features because they are suboptimal for the intended purpose.
Even authenticated and reliable images must still be interpreted by people with appropriate technical and content-based knowledge because these images are classified as semi-legible, meaning they are neither entirely legible nor impossible to read. Untrained viewers are not equipped to properly interpret and understand satellite and aerial imagery. The naïve belief that all images can be understood correctly without assistance can lead to erroneous interpretations. Further, the interpretation of images proffered by counsel in argument must be reasonably supported by the evidence presented. ICTY Investigator Jean-René Ruez put it well: “…intelligence, no matter how technologically advanced, cannot be disconnected from human reality—that is, testimony followed by verification in the field, in situ, in order to fit the pieces together. If the pieces are not put together, believing that a single piece of the puzzle gives an overall picture is the best way to make an error sooner or later.”
As with all image-based evidence, there may be states, organizations, and individuals who will use EOD for the purpose of fueling a misinformation campaign. EOD could be used to construct a false narrative, for example by overtly linking the images to an entirely different conflict or a different aspect of a relevant conflict. Any protocols for addressing such a risk of misinformation are largely creatures of the accountability mechanisms that utilize EOD as part of their visual analysis. Otherwise, independent guidance is increasingly provided in civil society and UN instructive documents. For example, the Berkeley Protocol emphasizes the value of geolocation and chronolocation as methods of confirming the temporal and spatial parameters of EOD, but the Protocol contains recommendations rather than mandated procedures. In practice, the ICC OTP’s investigators and analysts strive to ensure that potential EOD are valid and used for a proper purpose. Occasionally, a forensic imaging expert may be tasked with geolocating EOD. These confirmatory processes are only beginning to face some scrutiny in ICC chambers, as was raised by the defence in the Al Hassan case and which may be the subject of judicial commentary in the pending judgment.
Absent internationally applicable protocols, a concept which the authors support, the approaches taken to combat disinformation and error assessment may be influenced in large part by the ultimate end user of such evidence, i.e. the judiciary. Yet, rather than react to judicial commentary and rulings, it would be preferable to address this proactively. At present, there is a paucity of standardization of evidentiary procedures, for example concerning the quality of imagery collected, as well as whether it will be accessible to interested parties. While establishing international standards for image quality and accessibility would assist, a secondary concern is that enforceability of any such standard is likely to be elusive. This is because EOD is predominantly owned by private entities and States, both of which can limit access to or obscure EOD for political, economic, strategic, or other reasons.
For this reason, as EOD becomes more widespread in today’s satellite era, collaborative efforts—such as that of the initiative Space Evidence for Human Rights and IHL—are exploring innovative and interdisciplinary ways to enhance the use of EOD for accountability purposes.
Author Bios
Jonathan W. Hak KC PhD is a barrister and solicitor and international imagery law researcher and lecturer who teaches extensively in the UK, US, Canada, Singapore, and Europe on the legal and practical considerations involved in the effective use of image-based evidence in criminal prosecutions. The focus of his recent PhD work is on the use of non-textual evidence in international criminal prosecutions. He is the author of Image-Based Evidence in International Criminal Prosecutions: Charting a Path Forward (Oxford University Press, 2024). Jonathan was appointed Queen’s Counsel in 2006.
Sabrina K. Rewald JD LLM is an international legal consultant and a researcher at Leiden University’s Kalshoven-Gieskes Forum (‘KGF’) on International Humanitarian Law, where she supervises the KGF’s Digitally Derived Evidence (‘DDE’) Project and its Leiden Guidelines on the Use of DDE in International Criminal Courts and Tribunals. Sabrina is also a member of the Space Evidence for Human Rights and IHL collaboration and a Supervisory Board Member of OSINT for Ukraine. Sabrina is a licensed attorney in Michigan, U.S., and Ontario, Canada.