Offshore wind is an abundant energy resource contributing to diversifying energy portfolios around the world. In the United States, which has approximately 95,471 miles of shoreline, more than 128 million people—greater than 40 percent of the nation’s total 2021 population—reside in coastal counties where energy demand is high (NOAA, 2021a). Offshore wind energy development on the U.S. Outer Continental Shelf (OCS) is poised for further growth (NOAA, 2021b; NOAA and BEA, 2021) in order to meet increasing energy needs in a low-carbon, renewable way. However, the rapid development of offshore wind farms has implications for the safety of marine navigation in and around these facilities.
In January 2021, the Biden Administration issued Executive Order 14008 calling for the establishment of a new American infrastructure and clean energy economy, and prioritizing the expansion of U.S. offshore wind development as part of a government-wide approach to address climate change (United States Office of the Press Secretary, 2021a). This Executive Order recognized the need for close coordination and collaboration among federal agencies, states, the private sector, and other key stakeholders to accelerate offshore wind energy development, create jobs, and enhance the nation’s economy and security. Executive Order 14008 also directed the Secretary of the Interior to review siting and permitting processes in offshore waters to determine actions needed to increase renewable energy production, and resulted in the announcement of new leasing, funding, and development goals. The U.S. Departments of the Interior (DOI), Energy (DOE), and Commerce established the shared goal to deploy 30 gigawatts (GW) of U.S. offshore wind energy by 2030, while protecting biodiversity and encouraging co-use of the ocean by various stakeholders (DOI, 2021a; United States Office of the Press Secretary, 2021b).
In an effort to support the domestic offshore wind energy industry in meeting this 2030 target, DOI’s Bureau of Ocean Energy Management (BOEM) aimed to advance new lease sales and complete a review of at least 16 Construction and Operations Plans (COPs) by 2025, representing more than 19 GW of energy (Draher and Baker, 2021; United States Office of the Press Secretary, 2021b).
By September 2021, lessees of 14 offshore wind energy projects submitted COPs for technical and environmental review, as well as approval, disapproval, or approval with modifications by BOEM, thus entering into the final phase of the Bureau’s process for authorizing construction of wind energy facilities (BOEM, 2021a). Combined, proposed offshore wind capacity for these projects is 15.538–16.629 GW. Lease areas cover 1,637,992 acres of the U.S. OCS and are distributed along the Atlantic Coast from Massachusetts to North Carolina (Figure 1.1) (BOEM, 2021b; Draher and Baker, 2021). Three other leases, including one for a project led by Vineyard Wind, were currently undergoing site assessment (BOEM, 2021b). BOEM also announced a new priority Wind Energy Area in the New York Bight, located between the Long Island and New Jersey coast, adjacent to the largest metropolitan population center in the nation. While development and planning had thus far focused on the U.S. Atlantic OCS, the Biden Administration also announced a new interagency, state–federal effort to advance areas for offshore wind off the northern and central coasts of California, opening up the Pacific Coast to commercial-scale offshore clean energy projects (DOI, 2021b; United States Office of the Press Secretary, 2021c).
Offshore wind energy is relatively new to the United States. Since the world’s first offshore wind farm was installed in Vindeby, Denmark, in 1991 (5-megawatt [MW] capacity), offshore wind installations have become operational in several European nations including the United Kingdom, Germany, Denmark, Belgium, the Netherlands, Sweden, Finland, Portugal, Spain, Ireland, France, and Norway, as well as in Asian nations such as China, South Korea, Japan, Vietnam, and Taiwan (Figure 1.2). In the United States, the 30-MW, five-turbine Block Island Wind Farm in Rhode Island state waters became operational in 2016.1 The Coastal Virginia Offshore Wind Project resulted in the installation of two turbines in federal waters off of Virginia Beach, which have been operational since 2020 with a combined capacity of 12 MW.2 In 2020, China installed half of all new global offshore wind capacity (GWEC, 2021). An increase in capacity was recorded in Europe, primarily in the Netherlands and followed by Belgium, the United Kingdom, Germany, and Portugal, in addition to new installations in the United States and South Korea. As a result, approximately 5.5–6.1 GW of new offshore wind energy capacity was installed worldwide, resulting in a total offshore wind capacity of approximately 35 GW—4.8 percent of the total global cumulative wind power capacity (GWEC, 2021; Musial et al., 2021).
Concurrently, wind turbine generators (WTGs) have grown in size and capacity. Globally, from 2010 to 2019, the capacity-weighted average offshore turbine size has grown from 3.5 MW to more than 6 MW, and rotor (blade) diameters have grown from 100 meters (m) to more than 150 m.3 Taller WTG towers with larger blade lengths and capacities are planned for deployment in the coming decade (GE, 2018; Siemens Gamesa, 2020; Musial et al., 2021; Vestas, 2021). Upcoming COPs include WTGs with hub heights and rotor diameters approaching 175 m and 250 m, respectively, with most developers submitting WTG capacities of at least 14 MW (BOEM, 2021b; Draher and Baker, 2021).
The placement of WTGs throughout the Marine Transportation System has the possibility to conflict with historical shipping routes. While the U.S. Coast Guard seeks to provide the mariner with safe access to ports that align with historical shipping routes by designating shipping safety fairways and traffic separation schemes adjacent to the wind energy areas, some marine traffic will still transit through the wind farms. Commercial fishing vessels are expected to transit through wind farms to their fishing grounds from their homeport, while passenger vessels and recreational vessels may transit within the wind farms as a destination attraction. The requirement to orient the turbines in “straight rows or columns,” in at least “two lines of orientation,” is expected to provide consistent
planned spacing throughout the wind farm in an effort to minimize risks to surface vessels choosing to transit through. Even with a consistent orientation between wind farms, WTGs will impact visual navigation by hiding small contacts. If transiting through the wind farm during periods of restricted visibility, the mariner’s reliance on marine vessel radar (MVR) increases. Therefore, knowing the impacts WTGs have on MVR and possible mitigating solutions is critical to ensuring that navigation can continue by the safest means possible.
With hub heights exceeding 100 m, and structures predominantly made of steel,4 WTGs are large installations that can have significant electromagnetic reflectivity. As a result, WTGs installed within the line of sight of a radar system can cause clutter and interference, in some cases detrimentally impacting radar performance (Karlson et al., 2014). Furthermore, rotating blades can have large and numerous Doppler returns due to their motion relative to the radar system. The installation of WTGs across the U.S. OCS therefore poses potential conflicts with a number of radar missions supporting air traffic control, weather forecasting, homeland security, national defense, maritime commerce, and other activities relying on this technology for surveillance, navigation, and situational awareness (Gilman et al., 2016). In response to this observation, the U.S. Department of Defense, DOE, Federal Aviation Administration, and National Oceanic and Atmospheric Administration signed a memorandum of understanding to establish the interagency Wind Turbine Radar Interference Mitigation Working Group (WTRIM)5 to identify and develop mitigation solutions and strategies with an emphasis on WTG interference on aircraft and weather surveillance radar systems. U.S. Department of Homeland Security and BOEM personnel served as observers of the WTRIM, and BOEM joined as an active member in 2018. The WTRIM developed a Federal Interagency Wind Turbine Radar Interference Mitigation Strategy in 2016 to coordinate federal research and mitigation activities and encourage development of next-generation radar systems with resistance to turbine interference (Gilman et al., 2016). Of the multiple types of radar that may be affected by WTGs, this report specifically addresses radars used for marine navigation.
The U.S. OCS is a dynamic environment where a myriad of stakeholders intersects. The continued development of offshore energy installations in U.S. waters therefore has the potential to impact vessel navigation and safety in their vicinity (Detweiler, 2011). Responsible government agencies seek to reconcile where practicable any conflicts between stakeholder intersections, and, in this regard, consideration for the capabilities of MVR is an important issue. In 2016, the International Maritime Organization (IMO) recognized concerns of vessels operating in the vicinity of wind farms and amended its General Provisions on Ships’ Routeing (Resolution A.572(14), As Amended)6 to include the following paragraph in Section 3 (Responsibilities of Contracting Governments and recommended and mandatory practices):
3.14 In planning to establish multiple structures at sea, including but not limited to wind turbines, Governments should take into account, as far as practicable, the impact these could have on the safety of navigation, including any radar interference (IMO Resolution MSC.419 ).
6 See Resolution MSC.419(97) (adopted on November 25, 2016) regarding Amendments To The General Provisions On Ships’ Routeing (Resolution A.572(14), As Amended), https://wwwcdn.imo.org/localresources/en/KnowledgeCentre/IndexofIMOResolutions/MSCResolutions/MSC.419(97).pdf.
This amendment to the General Provisions on Ships’ Routeing internationally recognizes the potential impacts wind turbines could have on MVR and underscores the need to understand these impacts in the United States.
Through public outreach and engagement during the offshore renewable energy leasing process, BOEM has received input from commercial vessel maritime and commercial fishing industry stakeholders requesting further insight into the impacts of offshore wind energy installations on MVR7 (e.g., Salerno et al., 2019; WTRIM, 2020). MVRs have become a critical tool used by operators to navigate and avoid both collision and allision, especially under adverse weather conditions. Due to their size, structure, and proposed placement offshore, the maritime community expressed concern that WTGs may cast radar shadows, obfuscating smaller vessels exiting wind facilities in the vicinity of deep draft vessels in Traffic Separation Schemes. Commercial fisheries representatives raised concerns about the limited amount of research conducted on this topic, in addition to other possible forms of radar interference that may preclude safe navigation within an offshore wind facility, such as radar clutter and mirror effects (false signaling).8,9 As an example, Figure 1.3 shows a photograph of the radar display taken during the 2019 U.S. delegation visit to the United Kingdom’s Race Bank Wind Farm. It should be noted, however, that the photograph was not taken under a formal study framework and it is unclear whether the MVR was optimized for operation within the wind farm.
Few studies have explored WTG interference to MVR. In 2004, the U.K. Maritime and Coastguard Agency (MCA) and QinetiQ conducted a study at the North Hoyle Offshore Wind Farm comprised of 2-MW WTGs to assess impacts of WTGs on navigation systems, finding that the WTGs returned strong radar responses producing interfering echoes in both the X- and S-band type radars (Brown and Howard, 2004; MCA, 2008). It was reported that at close range, within 1.5 nautical miles (nmi) of the wind farm, WTGs may produce strong reflected, multiple, and sidelobe echoes that can mask or complicate the identification of real targets (Brown and Howard, 2004; MCA, 2008). Sidelobes are lobes in the antenna radiation pattern that are not in the direction of the main antenna beam. Authors of the 2004 MCA study noted that, while reducing receiver amplification would enable turbines in the main beam to be differentiated from sidelobe echoes on the radar monitor, therefore limiting potential for allision, this approach would also reduce the amplitude of other signals received by the radar from smaller vessels or buoys (Brown and Howard, 2004). Similar effects were explored in a 2007 British Wind Energy Association (BWEA) study evaluating WTG interference in the U.K. Kentish Flats Offshore Wind Farm, which features a grid of 30 3-MW WTGs (Marico Marine, 2007). The BWEA study identified wind farm–induced radar clutter, which could be accentuated depending on the positioning of radar infrastructure on the vessel. This study suggested that some of the observed clutter could be suppressed through adjustment of the radar controls, with the caveat that this technique could result in the loss of other targets with a small radar cross section (Marico Marine, 2007).
In 2008, radar modeling studies were commissioned by the developer of the Cape Wind farm and subsequently by the U.S. Coast Guard to assess the impact of proposed Cape Wind WTGs on marine radars operating in Nantucket Sound, resulting in the issuance of a Coast Guard assessment of moderate risk for the presence of WTGs on marine navigation in the area (U.S. Coast Guard Memorandum, 2009). More recently, a report prepared for DOE characterized the effects of offshore WTGs on multiple types of radar systems, such as shipborne, airborne, and coastal ocean-monitoring systems (Ling et al., 2013). Using modeled radar equipment simulating X- and S-band
7 Concerns regarding radar interference due to offshore WTGs are also articulated in public comments submitted to the U.S. Coast Guard Port Access Route Study: The Areas Offshore of Massachusetts and Rhode Island (USCG-2019-0131-0026). See https://www.regulations.gov/document/USCG-2019-0131-0026.
radar (which operate within one of two frequency bands centered on 9.4 gigahertz [GHz] in the X-band and 3 GHz in the S-band, depending on vessel size) used in the vicinity of the proposed Cape Wind farm, as well as a generic 10 × 10 WTG grid layout, authors of the 2013 DOE report observed that radar clutter caused by the presence of the wind farm can make it difficult to identify other vessels operating within the wind farm, but did not significantly affect tracking of vessels outside of the wind farm (Ling et al., 2013). They concluded that model results demonstrate a moderate impact on navigational X- and S-band radar (Ling et al., 2013). These and other studies will be discussed in Chapter 2 of this report.
While previous studies indicate that WTGs can affect MVR, they do not assess potential impacts based on the proposed WTG sizes and spacing for wind energy leases on the U.S. OCS seen in current COPs. For comparison, in 2007, the Kentish Flats Offshore Wind Farm featured 30 3-MW WTGs in a grid of east-west orientation and turbine spacing of 700 m (0.37 nmi) (Marico Marine, 2007); however, as one example, Ørsted’s proposed development of 1,100-MW Ocean
Wind I and 1,148-MW Ocean Wind II offshore of New Jersey plans to use more than 170 12-MW GE Haliade-X turbines spaced with a 1 nmi × 0.8 nmi separation (Ørsted, 2021). Adjacent Rhode Island and Massachusetts lease areas could hold hundreds of WTGs on the order of 12 MW each, with spacing up to 1 nmi or greater (BOEM, 2021b).
As momentum builds to deploy offshore wind energy across the U.S. OCS, and innovation in WTG engineering continues, the salient characteristics of offshore wind farms proposed for U.S. development have diverged from those of the Kentish Flats Wind Farm and others evaluated previously for interference on MVR. In light of the size and scope of proposed development in U.S. waters, maritime, commercial fishing industry, and other OCS stakeholders remain concerned and uncertain regarding the impacts of offshore WTGs to MVR, and the extent to which these impacts can hinder navigational awareness and safety within or adjacent to an offshore wind facility (e.g., Salerno et al., 2019; WTRIM, 2020).
In late 2020, BOEM called for a National Academies study to explore the impacts of WTGs on MVR used by vessel operators in and around offshore wind facilities. This report is a result of that study, which aims to determine and characterize the impacts of offshore WTGs on MVR, including radar commonly operated on large maritime commercial vessels and by commercial fishing vessels. Additionally, this study considers plausible techniques to mitigate WTG impacts in order to preserve MVR efficacy for navigational awareness and safety on vessels both in and near offshore wind facilities.
The statement of task for the study is presented in Box 1.1.
In 2021, members of the National Academies committee undertaking this study gathered information from public sessions with federal employees, industry representatives, researchers, and other stakeholders; written input accompanying these sessions; and review of the literature to develop this report and the recommendations and conclusions outlined herein. In order to clarify the scale, scope, and nature of WTG impacts on MVR, the committee organized its information-gathering efforts around six areas consistent with the study’s statement of task (Box 1.1): (1) navigation safety, (2) offshore WTG characteristics and deployment, (3) MVR design and operation, (4) electromagnetic characteristics of WTGs, (5) the impact of WTGs on MVR performance, and (6) mitigation strategies.
During the course of its deliberations, the committee identified that radar class (i.e., magnetron-based versus solid-state) is a discriminating factor in assessing both the impact of WTGs on performance and mitigating solutions. Moreover, as seen in the report, radar design choices affecting predominant electromagnetic phenomenology, such as operating frequency, are influential. However, other parameter variations, such as radar height, radar range, vessel type, and speed, do not result in unique insights, as phenomenology will be similar across these variables. Consistent with the statement of task, the report discusses key issues around WTG design and deployment impacts, with a primary focus on planned and future U.S. OCS deployment. The report’s discussion reflects these points and, as the reader will see, conveniently enables the report organization to follow the committee’s approach to information gathering.
Chapter 2 of this report provides background information on the navigation and safety issues associated with marine vessel operation in and adjacent to offshore wind facilities, common MVR designs and operation strategies for commercial maritime and fishing vessels in the United States, and electromagnetic characteristics of WTGs. This information clarifies the scale, scope, and nature of WTG impacts to MVR, which are also outlined in this chapter. Chapter 3 details mitigation solutions for WTG effects on MVR, including methods related to operational procedures, wind turbine design and deployment, radar design, signal and data processing, and other combined approaches. Chapter 3 also presents a general assessment of the feasibility of those methods. Lastly, Chapter 4 of this report provides a summary of key conclusions and recommendations resulting from the findings of the study committee, highlighting future directions for further consideration. Biographical information for committee members and definitions of acronyms used throughout the report may be found in Appendix A and Appendix B, respectively.
BOEM (U.S. Bureau of Ocean Energy Management). 2021a. Wind Energy Commercial Leasing Process. U.S. Department of the Interior. https://www.boem.gov/sites/default/files/documents/about-boem/Wind-Energy-Comm-Leasing-ProcessFS-01242017Text-052121Branding.pdf.
BOEM. 2021b. State Activities. https://www.boem.gov/renewable-energy/state-activities.
Brown, C., and M. Howard. 2004. Results of the Electromagnetic Investigations and Assessments of Marine Radar, Communications and Positioning Systems Undertaken at the North Hoyle Wind Farm by QinetiQ and the Maritime and Coastguard Agency. MCA Report MNA 53/10/366 or QINETIQ/03/00297/1.1. United Kingdom Maritime and Coastguard Agency. www.mgca.gov.uk.
Detweiler, G.H. 2011. Offshore Renewable Energy Installations. Impact on Navigation and Marine Safety. The Coast Guard Journal of Safety and Security at Sea Proceedings of the Marine Safety and Security Council 68(1):19-21. https://www.dco.uscg.mil/Portals/9/DCO%20Documents/Proceedings%20Magazine/Archive/2011/Vol68_No1_Spr2011.pdf?ver=2017-05-31-120645-040.
DOI (U.S. Department of the Interior). 2021a. Interior Joins Government-Wide Effort to Advance Offshore Wind. DOI Press Office, March 29. https://www.doi.gov/news/interior-joins-government-wide-effort-advance-offshore-wind.
DOI. 2021b. Biden-Harris Administration Advances Offshore Wind in the Pacific. DOI Press Office, May 25. https://www.doi.gov/pressreleases/biden-harris-administration-advances-offshore-wind-pacific.
Draher, J., and A. Baker. 2021. Lecture: Wind Turbine Generator Impacts to Marine Vessel Radar (BOEM 140M0121F0013). Presentation to the Committee on Wind Turbine Generator Impacts to Marine Vessel Radar, June 29, 2021. https://www.nationalacademies.org/event/06-29-2021/wind-turbine-generator-impacts-to-marine-vessel-radar-meeting-1.
GE (General Electric). 2018. GE Announces Haliade-X, the World’s Most Powerful Offshore Wind Turbine. General Electric. https://www.ge.com/news/press-releases/ge-announces-haliade-x-worlds-most-powerful-offshore-wind-turbine.
Gilman, P., L. Husser, B. Miller, and L. Peterson. 2016. Federal Interagency Wind Turbine Radar Interference Mitigation Strategy. U.S. Department of Energy. https://www.energy.gov/sites/default/files/2016/06/f32/Federal-Interagency-Wind-Turbine-Radar-Interference-Mitigation-Strategy-02092016rev.pdf.
GWEC (Global Wind Energy Council). 2021. Global Wind Report 2021, March 24. gwec.net/global-wind-report-2021/.
Karlson, B., B. LeBlanc, D. Minster, D. Estill, B. Miller, F. Busse, C. Keck, J. Sullivan, D. Brigada, L. Parker, R. Younger, and J. Biddle. 2014. Wind Turbine-Radar Interference Test Summary. Sandia Report: IFT&E Industry Report. Sandia National Laboratories. U.S. Department of Energy. https://www.energy.gov/sites/prod/files/2014/10/f18/IFTE%20Industry%20Report_FINAL.pdf.
Ling, H., M.F. Hamilton, R. Bhalla, W.E. Brown, T.A. Hay, N.J. Whitelonis, S. Yang, and A.R. Naqvi. 2013. Assessment of Offshore Wind Farm Effects on Sea Surface, Subsurface, and Airborne Electronic Systems. Final Report DE-EE0005380. U.S. Department of Energy. https://www.energy.gov/eere/wind/downloads/final-report-de-ee0005380-assessment-offshore-wind-farm-effects-sea-surface.
Marico Marine. 2007. Investigation of Technical and Operational Effects on Marine Radar Close to Kentish Flats Offshore Wind Farm Kentish Flats. BWEA (British Wind Energy Association) Technical Report, CCE5 No.1. London, UK: Department for Transport.
MCA (U.K. Maritime and Coastguard Agency). 2008. Offshore Renewable Energy Installations (OREIs): Guidance to Mariners Operating in the Vicinity of UK OREIs (MGN 372 (M+F)). File Ref. MNA/053/010/0626. https://www.gov.uk/government/publications/mgn-372-guidance-to-mariners-operating-in-vicinity-of-uk-oreis.
Musial, W., P. Spitsen, P. Beiter, P. Duffy, M. Marquis, A. Cooperman, R. Hammond, and M. Shields. 2021. Offshore Wind Market Report: 2021. DOE/GO-102021-5614. U.S. Department of Energy Office of Energy Efficiency and Renewable Energy, Wind Energy Technologies Office. https://www.energy.gov/sites/default/files/2021-08/Offshore%20Wind%20Market%20Report%202021%20Edition_Final.pdf.
NOAA (National Oceanic and Atmospheric Administration). 2021a. Economics and Demographics: NOAA Office for Coastal Management. https://coast.noaa.gov/states/fast-facts/economics-and-demographics.html.
NOAA. 2021b. Marine Economy in 2019 Outpaced U.S. Economy Overall. https://www.noaa.gov/news-release/marine-economy-in-2019-outpaced-us-economy-overall.
NOAA and BEA (Bureau of Economic Analysis). 2021. Marine Economy Satellite Account, 2014-2019. https://www.bea.gov/data/special-topics/marine-economy.
Ørsted (Ørsted Ocean Wind Initiative). 2021. Construction and Operations Plan. Ocean Wind Offshore Wind Farm (Volume 1, Prepared by FDR). Bureau of Ocean Energy Management. https://www.boem.gov/sites/default/files/documents/renewable-energy/state-activities/OCW01-COP-Volume-I.pdf.
Salerno, J., A. Krieger, M. Smead, and L. Veas. 2019. Supporting National Environmental Policy Act (NEPA) Documentation for Offshore Wind Energy Development Related to Navigation. OCS Study BOEM 2019-011:1–89. Washington, DC: U.S. Department of the Interior, Bureau of Ocean Energy Management.
Siemens Gamesa. 2020. Powered by Change: Siemens Gamesa Launches 14 MW Offshore Direct Drive Turbine with 222-meter Rotor. Siemens Gamesa Renewable Energy. https://www.siemensgamesa.com/newsroom/2020/05/200519-siemens-gamesaturbine-14-222-dd.
United States Office of the Press Secretary. 2021a. Executive Order on Tackling the Climate Crisis at Home and Abroad. The White House. https://www.whitehouse.gov/briefing-room/presidential-actions/2021/01/27/executive-order-on-tackling-the-climate-crisis-at-home-and-abroad/.
United States Office of the Press Secretary. 2021b. Fact Sheet: Biden Administration Jumpstarts Offshore Wind Energy Projects to Create Jobs. https://www.whitehouse.gov/briefing-room/statements-releases/2021/03/29/fact-sheet-biden-administration-jumpstarts-offshore-wind-energy-projects-to-create-jobs/.
United States Office of the Press Secretary. 2021c. Fact Sheet: Biden Administration Opens Pacific Coast to New Jobs and Clean Energy Production with Offshore Wind Development. https://www.whitehouse.gov/briefing-room/statements-releases/2021/05/25/fact-sheet-biden-administration-opens-pacific-coast-to-new-jobs-and-clean-energy-production-with-offshore-wind-development/.
U.S. Coast Guard Memorandum. 2009. Report of the Effects on Radar Performance of the Proposed Wind Farm Project and Advance Copy of the USCG Findings and Mitigations. https://www.boem.gov/sites/default/files/renewable-energy-program/Studies/FEIS/Appendix-M---USCG-Report.pdf.
Vestas. 2021. Vestas Launches the V236-15.0 Mw to Set New Industry Benchmark and Take Next Step Toward Leadership in Offshore Wind. Vestas Wind Systems A/S. https://www.vestas.com/en/media/company-news?l=42&n=3886820#!NewsView.
WTRIM (Wind Turbine Radar Interference Mitigation Working Group). 2020. Marine Navigation Radar. PowerPoint Presentation. Offshore Wind Turbine Radar Interference Mitigation Webinar Series: Technical Interchange Meeting. https://www.energy.gov/sites/prod/files/2020/07/f76/offshore-wind-turbine-radar-interference-mitigation-webinar-7-13-2020.pdf.