Velocity-Over-Ground Sensor for Inertial Navigation System Error Reduction

Navy SBIR 22.1 - Topic N221-046
NAVSEA - Naval Sea Systems Command
Opens: January 12, 2022 - Closes: February 10, 2022 (12:00pm est)

N221-046 TITLE: Velocity-Over-Ground Sensor for Inertial Navigation System Error Reduction



The technology within this topic is restricted under the International Traffic in Arms Regulation (ITAR), 22 CFR Parts 120-130, which controls the export and import of defense-related material and services, including export of sensitive technical data, or the Export Administration Regulation (EAR), 15 CFR Parts 730-774, which controls dual use items. Offerors must disclose any proposed use of foreign nationals (FNs), their country(ies) of origin, the type of visa or work permit possessed, and the statement of work (SOW) tasks intended for accomplishment by the FN(s) in accordance with the Announcement. Offerors are advised foreign nationals proposed to perform on this topic may be restricted due to the technical data under US Export Control Laws.

OBJECTIVE: Develop a velocity-over-ground sensor capability that accurately and covertly measures velocity relative to the ground for surface and subsurface naval platforms.

DESCRIPTION: Nearly all Navy platforms rely on Inertial Navigation Systems (INSs) to provide continuous position, attitude, and velocity information for accurate navigation. Without periodic external fix aiding, INS errors grow with time. However, INS errors can be controlled and reduced by employing various external position and velocity sources to bound and reduce errors. For example, use of velocity damping mechanisms can reduce velocity errors, which, when integrated, are the cause of navigation position errors. Ships systems integration enables the INS to receive Global Positioning System (GPS) updates to correct its velocity and position estimates and to detect sensor biases, but when GPS is unavailable, the system must rely on alternative sensors to maintain accuracy.

Currently, when GPS is not available, the electromagnetic log serves as this reference velocity source through the measurement, processing, and feedback of speed-through-water to the INS. Electromagnetic logs are reliable, passive, and covert, but they measure speed relative to surrounding water, rather than speed relative to the ground, and are subject to ocean currents and environmental distortions due to salinity, aeration, and temperature. The GPS, when unavailable, and electromagnetic logs are not adequate in providing velocity information for continual accurate navigation and currently there are no other solutions to fill the need. The velocity-over-ground sensor will complement, and in some cases, replace more conventional electromagnetic logs. In many operational scenarios, the velocity-over-ground sensor will enable superior navigation above and below the surface.

The Navy needs an innovative sensor that can determine velocity relative to the ground in the oceanic environment and under operating conditions typical to surface and subsurface naval vessels.

Typical conditions include:

  • Operating speeds in the range of 0 to 20 knots
  • Operational range/altitude from 10 to 6000 meters
  • Roll/pitch changes from ±5° to ±20°
  • Sea floor type variations from sand/gravel to mud
  • Water temperature in the range of 0°C to 30°C

The sensor may use any signal, modeling, or processing technique so long as it maintains a long-term velocity root-mean-square accuracy in the range of 0.2 m/s to 0.7 m/s. The specified accuracy range is a function of the minimum and maximum operating and environmental conditions described in the bulleted list above. For instance, the larger velocity variance is attributed to the maximum operating range, and vice versa. The sensor prototype may also utilize an external inertial navigation system as a co-sensor in a loose or tight coupling configuration, but target the same performance goals with size, weight, and power profile = 0.1m^3, 100kg, 100W. The proposed sensor prototype will be compared with conventional sensors and evaluated based on how well it performs under the typical conditions outlined.

Absent from the list are specific covertness metrics; however, covert operations are a significant attribute to subsurface naval operations. Conventional acoustic sensors can employ covert transmissions and avoid host vehicle detection with use of high transmit frequencies which demonstrate higher seawater absorption compared to lower frequency devices. However, conventional high-frequency sensors remain limited in their range of operations, limiting use to shallow waters. In this regard, there are design considerations such as signal bandwidth, transmit power, beam width, and unique wave forms, as well as transmitted acoustic frequencies that offer a trade space in performance. Covertness considerations, such as ocean bottom bounce impacts, bottom backscatter loss, transmit side-lobes, and noise, should be incorporated in the prototype sensor concept design process. Furthermore, the sensor prototype should be able to provide an underwater vehicle with velocity-over-ground without surface expression, enabling superior navigation in operational scenarios both above and below the surface.

As noted, acoustic sensors are potential solutions to this problem, but the standard Doppler velocity log (DVL) and correlation velocity log (CVL) approaches have downsides. Projecting acoustic waves into the environment broadcasts the location of the vessel and requires many assumptions about the sea floor which may not be valid in certain instances. An ideal acoustic sensor would compensate for operating depth, roll, pitch, sea floor bathymetry, or other relevant factors by combining different operational concepts with innovative methods and models. Currently, no generic acoustic solution exists. At-sea testing will be scheduled by the Government for using an inertial navigation system comparable to the WSN-7.

This product will find its greatest use in surface and subsurface environments where GPS is unavailable or degraded, and where highly accurate positioning is necessary. While velocity-over-ground measurements have proven applicable in Remotely Operated Vehicle (ROV), Autonomous Underwater Vehicle (AUV), and towed vehicle navigation, the sensor prototype sought here supports inertial navigation correction and integration in large-scale naval platforms capable of surveying 95% of the world’s ocean depths.

Work produced in Phase II may become classified. Note: The prospective contractor(s) must be U.S. Owned and Operated with no Foreign Influence as defined by DOD 5220.22-M, National Industrial Security Program Operating Manual, unless acceptable mitigating procedures can and have been implemented and approved by the Defense Counterintelligence Security Agency (DCSA), formerly the Defense Security Service (DSS). The selected contractor must be able to acquire and maintain a secret level facility and Personnel Security Clearances, in order to perform on advanced phases of this contract as set forth by DCSA and NAVSEA in order to gain access to classified information pertaining to the national defense of the United States and its allies; this will be an inherent requirement. The selected company will be required to safeguard classified material IAW DoD 5220.22-M during the advance phases of this contract.

PHASE I: Develop a concept for a velocity-over-ground sensor that meets the parameters in the Description. Demonstrate its technical feasibility using analytical models, simulations, and testing. The modeling effort should consider a list of potential noise sources and characterize their potential impact on the overall measurement accuracy of a hypothetical sensor. Develop a trade space analysis to identify optimal covertness while achieving performance targets. The Phase I Option, if exercised, will include the initial design specifications and capabilities description to build a prototype solution in Phase II.

PHASE II: Develop and deliver a prototype velocity-over-ground sensor based on the results of Phase I. Demonstrate the prototype meets the parameters of the Description through initial laboratory testing to confirm the design, functioning of components, and physical model underlying the theory of measurement for the sensor.

It is probable that the work under this effort will be classified under Phase II (see Description section for details).

PHASE III DUAL USE APPLICATIONS: Assist the Navy in transitioning the velocity-over-ground sensor prototype through testing and further development to facilitate the adaptation of the technology to Navy use. The final product will be tested and verified according to the relevant military specifications for Navy use.

The technology is expected to be of use in the commercial manufacturing industry for AUVs for exploration and other sea floor uses.


  1. P. Denbigh. "Ship velocity determination by Doppler and correlation techniques." IEE Proceedings, Vol. 131, Part F, No. 3 (1984).
  2. M. Lanzagorta, J. Uhlmann and S. E. Venegas-Andraca. "Quantum sensing in the maritime environment/" Oceans 2015 - MTS/IEEE Washington, Washington, DC, (2015)
  3. S. Shady, A. Moussa, A. Sesay. "A new velocity meter based on Hall effect sensors for UAV Indoor Navigation." IEEE Sensors Journal, Vol. 19, No. 8, APRIL 15 (2009)
  4. T. Blanford, D. Brown, and R. Meyer. "Design considerations for a Compact Correlation Velocity Log." Proceedings of Meetings on Acoustics, Vol. 33 (2018)

KEYWORDS: Correlation Velocity Log; Electromagnetic Log; Doppler Velocity Log; GPS Challenged Environments; Inertial Navigation; Velocity-over-Ground Sensor


The Navy Topic above is an "unofficial" copy from the overall DoD 22.1 SBIR BAA. Please see the official DoD Topic website at for any updates.

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