All maritime navigators (should) know by heart Rule 5 of the 1972 Convention on the International Regulations for Preventing Collisions at Sea (Colregs for short): “Every vessel shall at all times maintain a proper lookout by sight and hearing as well as by all available means appropriate in the prevailing circumstances and conditions so as to make a full appraisal of the situation and of the risk of collision.”
Analogously, now that positioning, navigation and timing (PNT) data have become essential to the functioning of critical infrastructure and many other aspects of advanced industrial economies, it is imperative that we use “all available means” to maintain and improve that data’s accuracy, integrity, availability, continuity and coverage.
Given the inherent limitations of GNSS and the growing threat of jamming and spoofing, those means must also include other technologies, both legacy and emerging — such as L-band and S-band broadcasts from GEO and LEO satellites, fiber-optic timing systems, optical-based absolute positioning solutions, map-matching databases, inertial measuring units (IMUs), ultra-wideband and terrestrial radiofrequency (RF) technologies across low frequency (LF), medium frequency (MF), ultra-high frequency (UHF) and Wi-Fi/802.11 spectrum bands.
In March 2024, the U.S. Department of Transportation (DOT) — the lead for civil PNT requirements in the United States — released its updated Complementary PNT Action Plan: DOT Actions to Drive CPNT Adoption. It builds on Executive Order 13905, Strengthening National Resilience Through Responsible Use of Positioning, Navigation, and Timing Services; Space Policy Directive 7, The United States Space-Based Positioning, Navigation and Timing Policy; and DOT’s own 2021 report to Congress, Complementary PNT and GPS Backup Technologies Demonstration Report.
DOT’s Action Plan establishes five broad lines of effort:
1. Stakeholder engagement
2. Specs and standards development
3. Field trial and test range development
4. Establish a Federal PNT Services Clearinghouse
5. Domain-specific CPNT Services acquisition support
The plan explicitly extends the National Space-Based PNT Advisory Board’s chosen strategy of “protect, toughen, and augment” (PTA) to “protect, toughen, augment, and adopt” (PTAA).
It points out that “[s]trengths and vulnerabilities of existing complementary PNT sources can vary based on the specific application and operating environment.” For example, a ship at sea need not worry about multipath and can tolerate relatively large position errors that are unacceptable for, say, an autonomous car. The latter, however, can take advantage of nearby transmitters for ground-based solutions, as well as landmarks for self-localization. Different options for different needs.
On the last page, in a chart illustrating its “preliminary milestones and functional activities associated with implementing this action plan,” DOT lists eLoran infrastructure as one of the areas of R&D — starting with a demonstration project in the last quarter of 2023 followed by, in 2024 and 2025, “evaluate eLoran service against CPNT measures of effectiveness.”
eLoran, too. All available means.
<p>The post First Fix: By all available means first appeared on GPS World.</p>
