Sensors, ASA(ALT), Phase I
Dynamic Hartmann Turbulence Sensor Processing
Topic Objective
Army SMDC aims to reconstruct the vertical profile of turbulence (Cn2) as a function of height above ground using a Hartmann Turbulence Sensor (HTS) mounted on a tracking gimbal and platform that lifts 1000 meters off the ground. The goal of this SBIR grant is to develop a system including a beacon, turbulence sensor and data collection methodology to collect and process dynamic optical turbulence data from the sensor to measure the turbulence with consideration to the rate of movement of the beacon platform.
Description
As modern laser weapon systems are becoming more prevalent, measuring atmospheric turbulence for predicting the laser system effectiveness will be of great concern. Of particular interest is the variation in atmospheric turbulence as a function of height above ground. Among the most proliferated and trusted atmospheric turbulence measurements, is the Hartmann Turbulence Sensor (HTS). This sensor requires an optical source (beacon) to be placed at some distance from the sensor head and for an integrated turbulence measurement to be performed along the path. Consequentially, turbulence measurements with HTS have been restricted to static, near ground paths only.
There are numerous challenges to overcome to obtain turbulence measurements as a function of height, which can be achieved by elevating the beacon on a platform (e.g. Unmanned Aircraft System). Some challenges include existing hardware constraints in both the turbulence sensors and beacons. Turbulence sensors typically have very narrow fields of view which requires very accurate pointing. Similarly, beacons are typically limited in beam width to less than 10 degrees and must be accurately and actively pointed at the sensor on the ground to prevent loss of signal. This SBIR grant shall include research on how to implement the entire data collection system and data processing required to accurately reconstruct the vertical Cn2 profile.
The proposal for this effort shall include details on how to construct the data collection hardware including mounting a beacon a platform (e.g. UAS) with pointing ability, identifying a turbulence sensor to be used (e.g. Shack Hartmann Wavefront Sensor), and tracking capability for the turbulence sensor. The proposal shall address the necessary data collection rates of the turbulence sensor to measure the turbulence with consideration to the rate of movement of the beacon platform. There are two different data processing functions that should be researched and developed in order to provide the complete solution that is required of this program. The first is the conversion of raw Shack-Hartmann wavefront sensor (SHWFS) data to atmospheric turbulence parameters such as the Fried coherence length (r0) and the refractive index structure function, Cn2. The second function is the reconstruction of the vertical turbulence profile using the full data set captured over a complete beacon ascent. The SHWFS data processing should consider the following established methods as a minimum; differential image motion (DIMM), difference of differential tilt variance (DDTV), and differential scintillation. Other methods as well as new innovations in this area are encouraged but their performance in comparison to the above listed methods should be well documented. The vertical profile reconstruction problem should consider iterative stepwise solutions as well as more optimized simultaneously solved system solutions in order to overcome the noise amplification problems that are expected with the iterative solutions.
Phase I
The Phase 1 effort will use wave optics generated (simulated) HTS data to establish the minimum requirements for the HTS and to develop the processing algorithms. The outcome of this work will be to develop, demonstrate, and deliver the processing algorithms that can optimally process the HTS data and reconstruct the vertical turbulence profile. The accuracy limitations and its dependence on HTS design parameters such as frame rate, SHWFS resolution, noise, beacon ascent rate, as well as any other pertinent parameters will be fully defined and described.
Phase II
The results of the Phase I designs will be utilized to establish the design requirements for an optimized HTS prototype system. This HTS system will be built and then used to collect dynamic HTS data which will be used to further develop and demonstrate the processing methods developed in Phase I.
Phase III
High energy DoD laser weapons offer benefits of graduated lethality, rapid deployment to counter time-sensitive targets, and the ability to deliver significant force either at great distance or to nearby threats with high accuracy for minimal collateral damage. Knowledge of the atmospheric turbulence along the shot path is a key limiting factor for lethality and as such it is a critical input for the fire control system.
The Phase III effort shall be to design and build a system that could be integrated into an Army’s High Energy Laser Weapon System for real time use as part of the fire control system. Military funding for this Phase III effort would be executed by the U.S. Army Space and Missile Defense Technical Center as part of its Directed Energy research.
Submission Information
To submit full proposal packages, and for more information, visit the DSIP Portal.
References:
Andrei Tokovinin, “Measurement of seeing and the atmospheric time constant by differential scintillations,” Appl. Opt. 41, 957-964 (2002)
David L Fried, “Differential angle of arrival’ Theory, evaluation, and measurement feasibility” Radio Science, Vol. 10, No. 1. pp71-76, Jan 1975.
Matthew R. Whiteley, Donald C. Washburn, Lawrence A. Wright, “Differential-tilt technique for saturation-resistant profiling of atmospheric turbulence,” Proc. SPIE 4494, Adaptive Optics Systems and Technology II, (4 February 2002); https://doi.org/10.1117/12.454795
Terry J. Brennan, David C. Mann, “Estimation of optical turbulence characteristics from Shack Hartmann wavefront sensor measurements”, Proc. SPIE 7816, Advanced Wavefront Control: Methods, Devices, and Applications VIII, 781602 (12 August 2010); doi: 10.1117/12.862808
Topic Objective
Army SMDC aims to reconstruct the vertical profile of turbulence (Cn2) as a function of height above ground using a Hartmann Turbulence Sensor (HTS) mounted on a tracking gimbal and platform that lifts 1000 meters off the ground. The goal of this SBIR grant is to develop a system including a beacon, turbulence sensor and data collection methodology to collect and process dynamic optical turbulence data from the sensor to measure the turbulence with consideration to the rate of movement of the beacon platform.
Description
As modern laser weapon systems are becoming more prevalent, measuring atmospheric turbulence for predicting the laser system effectiveness will be of great concern. Of particular interest is the variation in atmospheric turbulence as a function of height above ground. Among the most proliferated and trusted atmospheric turbulence measurements, is the Hartmann Turbulence Sensor (HTS). This sensor requires an optical source (beacon) to be placed at some distance from the sensor head and for an integrated turbulence measurement to be performed along the path. Consequentially, turbulence measurements with HTS have been restricted to static, near ground paths only.
There are numerous challenges to overcome to obtain turbulence measurements as a function of height, which can be achieved by elevating the beacon on a platform (e.g. Unmanned Aircraft System). Some challenges include existing hardware constraints in both the turbulence sensors and beacons. Turbulence sensors typically have very narrow fields of view which requires very accurate pointing. Similarly, beacons are typically limited in beam width to less than 10 degrees and must be accurately and actively pointed at the sensor on the ground to prevent loss of signal. This SBIR grant shall include research on how to implement the entire data collection system and data processing required to accurately reconstruct the vertical Cn2 profile.
The proposal for this effort shall include details on how to construct the data collection hardware including mounting a beacon a platform (e.g. UAS) with pointing ability, identifying a turbulence sensor to be used (e.g. Shack Hartmann Wavefront Sensor), and tracking capability for the turbulence sensor. The proposal shall address the necessary data collection rates of the turbulence sensor to measure the turbulence with consideration to the rate of movement of the beacon platform. There are two different data processing functions that should be researched and developed in order to provide the complete solution that is required of this program. The first is the conversion of raw Shack-Hartmann wavefront sensor (SHWFS) data to atmospheric turbulence parameters such as the Fried coherence length (r0) and the refractive index structure function, Cn2. The second function is the reconstruction of the vertical turbulence profile using the full data set captured over a complete beacon ascent. The SHWFS data processing should consider the following established methods as a minimum; differential image motion (DIMM), difference of differential tilt variance (DDTV), and differential scintillation. Other methods as well as new innovations in this area are encouraged but their performance in comparison to the above listed methods should be well documented. The vertical profile reconstruction problem should consider iterative stepwise solutions as well as more optimized simultaneously solved system solutions in order to overcome the noise amplification problems that are expected with the iterative solutions.
Phase I
The Phase 1 effort will use wave optics generated (simulated) HTS data to establish the minimum requirements for the HTS and to develop the processing algorithms. The outcome of this work will be to develop, demonstrate, and deliver the processing algorithms that can optimally process the HTS data and reconstruct the vertical turbulence profile. The accuracy limitations and its dependence on HTS design parameters such as frame rate, SHWFS resolution, noise, beacon ascent rate, as well as any other pertinent parameters will be fully defined and described.
Phase II
The results of the Phase I designs will be utilized to establish the design requirements for an optimized HTS prototype system. This HTS system will be built and then used to collect dynamic HTS data which will be used to further develop and demonstrate the processing methods developed in Phase I.
Phase III
High energy DoD laser weapons offer benefits of graduated lethality, rapid deployment to counter time-sensitive targets, and the ability to deliver significant force either at great distance or to nearby threats with high accuracy for minimal collateral damage. Knowledge of the atmospheric turbulence along the shot path is a key limiting factor for lethality and as such it is a critical input for the fire control system.
The Phase III effort shall be to design and build a system that could be integrated into an Army’s High Energy Laser Weapon System for real time use as part of the fire control system. Military funding for this Phase III effort would be executed by the U.S. Army Space and Missile Defense Technical Center as part of its Directed Energy research.
Submission Information
To submit full proposal packages, and for more information, visit the DSIP Portal.
References:
Andrei Tokovinin, “Measurement of seeing and the atmospheric time constant by differential scintillations,” Appl. Opt. 41, 957-964 (2002)
David L Fried, “Differential angle of arrival’ Theory, evaluation, and measurement feasibility” Radio Science, Vol. 10, No. 1. pp71-76, Jan 1975.
Matthew R. Whiteley, Donald C. Washburn, Lawrence A. Wright, “Differential-tilt technique for saturation-resistant profiling of atmospheric turbulence,” Proc. SPIE 4494, Adaptive Optics Systems and Technology II, (4 February 2002); https://doi.org/10.1117/12.454795
Terry J. Brennan, David C. Mann, “Estimation of optical turbulence characteristics from Shack Hartmann wavefront sensor measurements”, Proc. SPIE 7816, Advanced Wavefront Control: Methods, Devices, and Applications VIII, 781602 (12 August 2010); doi: 10.1117/12.862808