LIDAR on Manned and Unmanned Airborne Platforms: Uncovering Hidden Targets Beneath Foliage

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Introduction:

In the realm of remote sensing technologies, Light Detection and Ranging (LIDAR) has emerged as a game-changer for detecting and mapping targets obscured by dense foliage. Whether deployed on manned or unmanned airborne platforms, LIDAR’s ability to penetrate vegetation can reveal previously hidden objects and provide critical insights in various fields, from military reconnaissance to environmental monitoring and disaster response. This article delves into the applications and advantages of LIDAR on manned and unmanned airborne platforms for detecting targets concealed beneath dense foliage.

 

Challenge of detecting under Foliage

Situation awareness and accurate target identification are critical requirements both for security forces engaged in counterterrorism operations. Ground, airborne and space-borne radars and EO sensors have proved to be of great utility in  detection, tracking, and imaging of  vehicles to  high speed fighter aircrafts,   locating mortars and artillery,  over the horizon capability and all weather long range surveillance.

However theses sensors are limited in capability to detect targets concealed in the foliage. Conventional forces and terrorists / insurgents have exploited this weakness by employing camouflage, concealment and deception tactics like hiding in camouflage net and forests since long.

Understanding LIDAR Technology:

LIDAR (Light Detection and Ranging) is a remote sensing technology that uses laser pulses to measure distances and create highly detailed maps of the surrounding environment. It operates on the principle of emitting laser beams and measuring the time it takes for the light to bounce back after hitting objects in its path. By analyzing the properties of the returned light, LIDAR systems provide valuable information about the shape, composition, and spatial distribution of objects or surfaces.

The fundamental components of a LIDAR system include a laser source, a scanner or emitter, a receiver, and data processing software. The laser source emits short, intense pulses of laser light, typically in the near-infrared spectrum. The emitted laser pulses travel through the atmosphere and interact with objects or surfaces, either by scattering, reflection, or absorption.

When a laser pulse encounters an object or surface, a portion of the light is reflected back towards the LIDAR system. The receiver in the LIDAR system detects and measures the intensity and time-of-flight of the reflected light. By precisely measuring the time it takes for the light to return to the receiver, the LIDAR system can calculate the distance to the object or surface with high accuracy.

LIDAR technology finds applications in numerous fields, including geology, forestry, urban planning, transportation, environmental monitoring, and security. It is used to create precise elevation maps, monitor vegetation, assess the impact of natural disasters, analyze pollution levels, detect changes in land use, and aid in the planning of infrastructure projects.

LIDARs for Foliage detection

LIDARs  are rapidly gaining maturity as  very capable sensors for number of applications such as imaging through clouds, vegetation and camouflage, 3 D mapping and terrain visualization, navigation and obstacle avoidance for robotics as well as weapon guidance.

By analyzing the return signal, LIDAR systems can create detailed 3D representations of objects and terrain features, including those obscured by vegetation cover. Traditional optical sensors struggle to penetrate foliage, but LIDAR can capture information even beneath the canopy.

LIDAR wavelength is much shorter than microwave, hence it is considered incapable of penetrating forest canopy. However even in high density forests there are gaps including gaps inside single tree crown and gaps in between different tree canopies. If portion of laser beam is able to penetrate the gap and hit the target and return to the detector, the LIDAR is able to detect the target hidden under foliage.

LIDAR on Manned Airborne Platforms:

LIDAR (Light Detection and Ranging) is an active optical remote sensing sensor, that when flown aboard rotary or fixed-wing aircraft, through illumination of the target scene  with laser pulses can acquire x, y, and z coordinates of both manmade and naturally occurring targets and generate 3D models of them.

• Wide Coverage: Manned aircraft can cover extensive areas quickly, making them ideal for large-scale surveys.
• High-Resolution Data: Advanced LiDAR systems on manned platforms provide high-resolution data, enabling detailed analysis.
• Flexibility: Piloted aircraft can adapt to changing conditions and alter flight paths as needed for optimal data collection.

Manned aircraft equipped with LIDAR systems have long been utilized in various industries, including forestry, infrastructure planning, and urban mapping. When it comes to detecting targets under dense foliage, manned platforms offer the advantage of carrying larger and more powerful LIDAR systems, capable of acquiring high-resolution data over vast areas. This makes them ideal for large-scale environmental surveys and disaster response efforts.

Applications on Manned Platforms:

1. Forest Monitoring: Manned airborne LIDAR is extensively used for monitoring forest health, estimating biomass, and identifying potential hazards like diseased trees or insect infestations, all of which can be hidden beneath thick vegetation.
2. Archaeological Exploration: In archaeology, LIDAR-equipped aircraft can reveal ancient ruins and archaeological sites hidden in dense jungles or heavily vegetated landscapes, providing valuable information to researchers and conservationists.
3. Infrastructure Inspection: LIDAR on manned platforms aids in inspecting power lines, pipelines, and other critical infrastructure obscured by foliage, facilitating early detection of potential vulnerabilities.

For deeper understanding of Airborne LIDARs and applications please visit: Airborne LiDAR Technologies: Advancing Remote Sensing in Environmental Monitoring, Security, and Beyond

LIDAR on Unmanned Airborne Platforms (UAVs):

Unmanned Aerial Vehicles (UAVs) have revolutionized remote sensing by offering flexibility, cost-effectiveness, and the ability to access hard-to-reach areas. These platforms offer a cost-effective and versatile alternative to manned aircraft, especially for smaller or more targeted survey areas. UAV-based LIDAR systems have proven particularly valuable for detecting targets hidden beneath foliage due to their maneuverability and adaptability.

Applications on UAV Platforms:

1. Precision Agriculture: UAV-based LIDAR enables farmers to monitor crop health and assess vegetation density, aiding in precision agriculture practices and optimizing irrigation and fertilization.
2. Environmental Conservation: UAVs equipped with LIDAR can survey dense forests and wildlife habitats, providing crucial data for biodiversity assessment and conservation efforts.
3. Disaster Response: In the aftermath of natural disasters, UAV-based LIDAR can quickly assess damaged areas, helping emergency responders identify blocked roads and infrastructure hidden under debris and vegetation.

Advantages of UAV-based LIDAR:

• Flexibility and Versatility: UAVs equipped with LIDAR can access challenging terrains, such as steep mountains or dense jungles, which may be difficult or dangerous for manned aircraft.
• Precision: Drones can fly at lower altitudes and slower speeds, providing highly detailed and precise data.
• Rapid Deployment: UAVs can be deployed swiftly for on-demand data acquisition, making them ideal for real-time monitoring and urgent disaster response.
• Cost-Effectiveness: Compared to manned flights, UAV-based LIDAR missions are more cost-effective, allowing for more frequent and targeted data collection.

Uncovering Hidden Targets Beneath Foliage

Forestry and Vegetation Management

In forestry, LiDAR is invaluable for mapping tree canopy structure, measuring tree heights, and assessing forest biomass. By penetrating through foliage, LiDAR provides detailed information about the forest floor, helping in the management and conservation of forests.

Applications:

• Forest Inventory: Accurate measurement of tree species, density, and health.
• Wildfire Management: Identifying fuel loads and potential firebreaks.
• Habitat Assessment: Mapping critical habitats for wildlife conservation.

Archaeology

LiDAR has revolutionized archaeology by revealing ancient structures and landscapes hidden beneath dense vegetation. This non-invasive technology allows archaeologists to uncover hidden features without disturbing the site.

Applications:

• Site Discovery: Identifying previously unknown archaeological sites.
• Landscape Analysis: Mapping ancient road networks, terraces, and settlements.
• Preservation: Documenting and preserving sites for future research.

Military and Security

In military and security applications, LiDAR is used to detect hidden threats and gather intelligence in forested or jungle environments. The ability to see through foliage provides a tactical advantage in reconnaissance and surveillance operations.

Applications:

• Threat Detection: Identifying hidden enemy positions or equipment.
• Terrain Mapping: Creating detailed maps for mission planning.
• Border Security: Monitoring forested borders for illegal activities.

Successful Foliage penetrating LIDAR developments

Now, researchers at the Naval Research Laboratory in Washington, DC,  have developed  LIDAR based on gated digital holography, to give LiDAR an enhanced ability to see through obscuring elements like foliage and netting.“see” through minor obstructions for genuine obstacles.

A team at MIT’s Photonic Microsystems Group have integrated LIDAR systems onto a single microchip that can be mass produced in commercial CMOS foundries yielding a potential on-chip LIDAR system cost of about $10 each. Instead of a mechanical rotation system, optical phased arrays with multiple phase controlled antennas emitting arbitrary beam patterns may make devices more robust.

Naval Research Laboratory has developed a foliage penetrating LIDAR

Researchers at Washington, DC’s Naval Research Laboratory have developed a LIDAR and a new methodology based on gated digital holography, to give LiDAR an enhanced ability to see through obscuring elements like foliage and netting.

“This was an attempt to address one of the problems with something called foliage-penetrating LiDAR,” Paul Lebow of the Naval Research Laboratory said. “You can actually use it to detect three-dimensional images behind an obscuration such as a tree canopy… You can illuminate using LiDAR through the leaves and get enough light coming back through to be able to recreate a three-dimensional, topographic view of what’s going on beneath.”

However, over the years,  LiDAR measurements have been limited to wherever light can penetrate. With surfaces hidden behind obstructions, the original light gets thrown away and the camera is unable to detect or only receives a limited signal, providing minimal readings.

“We have been working with a process called optical phase conjugation for quite some time and it dawned on us that we might be able to use that process to essentially project a laser beam through the openings of the leaves and be able to see through a partial obscuration,” Lebow said. “It was something that until maybe the last five years was not viable just because the technology wasn’t really there.”

The stuff we had done about 20 years ago involved using a nonlinear optical material and was a difficult process. Now everything can be done using digital holography and computer generated holograms, which is what we do.” This new system uses a specially designed laser that alone took a year and a half to develop, but was a necessary component according to Lebow and his colleague, Abbie Watnik, who is also at the Naval Research Laboratory and another of the work’s authors.

Phase conjugation is a fascinating phenomenon with very unusual characteristics and properties. It operates somewhat like holography, but it is a dynamic hologram, whose “holographic plate” is defined by interfering wave fronts in a nonlinear optical medium, rather than etched as a static pattern on a glass plate. Optical phase conjugation is a non-linear optical process, which is capable of time reversing the scattering process, and healing the distortions in a wave front.

“We send one laser beam out to the target and then it returns, and at the exact same time that return [beam] hits the detector, we interfere it locally with another laser beam,” Watnik said. The researchers needed to design the laser system to ensure the camera captures absolute coherence when the laser beams interfere with one another.

Using a pulsed laser with pulse widths of several nanoseconds, and gated measurements with similar time resolution, the holographic system selectively blocks the earliest-to-arrive light reflecting obscurations. The camera then only measures light coming back from the partially hidden surface below.

“We’ve done this earlier using a CW (continuous-wave) laser as a demo, but now we’re using a pulsed laser and a very fast gated sensor that can turn on at the appropriate time to basically only let us respond to the light coming from where we want it to come from, from the target,” Lebow said. “The laser is designed so that the time difference between the local reference pulse and the signal pulse that comes back from the target is completely adjustable to accommodate distances from a few feet to several kilometers.”

“We were able to verify what our computer model says using our real data – matching it to what we actually see using the spatial light modulator, so I think that was an interesting verification of our results,” Watnik said.

Watnik and Lebow, along with their research team, hope to continue with the project and make the adaptations to their prototype necessary to making the foliage-penetrating LiDAR system field-ready.

US Army Requirements for State-of-the-Art Imaging LIDAR for Tactical Mapping from UAVs

The Army Contracting Command has issued a source-sought notice (W909MY-17-R-A006) for a LIDAR payload designed for both manned and unmanned airborne platforms. The system must support mission planning, tactical mapping, concealed target detection (Multi-Aspect Foliage Penetration [FOPEN]), and other mapping missions.

Key Requirements:

1. Advanced Technology Demonstrator Prototype:
   • LIDAR technologies must be mature enough for an advanced technology demonstrator prototype.
   • The imaging sensor must include a pointing and stabilization unit, such as a stabilized turret, which houses the sensor optics, focal planes, and supporting electronics.
2. Data Storage and Processing:
   • The system must incorporate a computer for data storage and sensor processing, along with necessary algorithms for sensor processing and imaging sensor command and control software.
3. Operational Specifications:
   • Variable swath capability from 200 meters to over 1 km.
   • Slant range capability up to 25,000 feet.
   • Range resolution (ability to separate objects in range with a minimal number of laser pulses) under one meter.
   • Range precision (statistical distribution of a number of measurements over a fixed range) under 10 cm.
   • Field of regard of at least ±35 degrees in-track and ±45 degrees cross-track.
4. Platform Considerations:
   • Primary deployment on unmanned airborne platforms.
   • Weight and aerodynamic drag (primarily front cross-section diameter) are critical concerns.
5. System Components:
   • The LIDAR system will consist of multiple Line Replaceable Units (LRUs), including:
     • Imaging Sensor Unit (ISU): Contains pointing and stabilization unit, sensor optics, focal planes, and supporting electronics. Must include any external electronics boxes in weight calculations.
     • Storage and Processing Unit (SPU): Includes the storage and processing computer and the algorithms for data processing and exploitation. Hosts command, control, and status software for the ISU.

LIDAR system’s PSU shall store and process the ISU’s imagery. The government desires automated feature extraction (AFE) and/or aided target recognition (AiTR) algorithms and transmission of a low-resolution orthographic projection of the human activity layer (HAL) annotated with anomaly detections. The Vendor, in response to the processing solution, should discuss any AFE and AiTR algorithms they currently possess. Examples include anomaly detection, segmentation, void detection, plane detection, or any algorithm or tool to minimize analysts’ workload and facilitate operation over limited bandwidth communications (<= 2 Mbps)

DARPA’s Modular Optical Aperture Building Blocks (MOABB)

The MIT Photonic Microsystems Group is working to miniaturize large, expensive, mechanical LIDAR systems by integrating them onto microchips that can be mass-produced in commercial CMOS foundries. This initiative began with the development of 300-mm silicon photonics at MIT, potentially reducing production costs to about $10 per unit at production volumes of millions per year.

MIT’s On-Chip LIDAR System:

• Current Capabilities: Detects objects at ranges up to 2 meters.
• Future Goals: Achieve a 10-meter range within a year and eventually reach a 100-meter range or more.
• Resolution: Demonstrated centimeter longitudinal resolution and anticipated 3-cm lateral resolution at 2 meters.
• Minimum Range: Approximately 5 cm.

DARPA’s MOABB Program:

DARPA’s MOABB program aims to develop ultracompact LIDAR systems that use light to image objects and their motions similarly to how RADAR systems use radio waves.

1. Phase 1:
   • Objective: Develop speck-sized light-emitting and light-detecting cells.
   • Integration: Ensure these cells can be integrated into larger arrays using standard semiconductor manufacturing processes.
2. Phase 2 and Phase 3:
   • Objective: Integrate these cells into larger arrays.
   • Array Sizes: Create a 1 cm² array and a 10 cm² array with upwards of 100 and 10,000 unit cells, respectively.
3. Final Goal:
   • Aperture Size: Develop a 10-cm aperture LIDAR surface.
   • Complexity: Potentially the most complex electronic-photonic circuit ever constructed, integrating digital, electronic, optical, and radiofrequency elements across various semiconductor materials.

Potential Applications:

• Foliage-Penetrating Imagers: Spot hidden threats under dense forests, such as snipers or tanks.
• Collision Avoidance: For small unmanned aerial vehicles (UAVs) maneuvering in tight indoor spaces.
• Precision Motor Control: For robotic limbs and fingers.
• High-Capacity Communications: Light-based communications and data-transfer systems.
• Gaming and Training Modules: LIDAR technology could create immersive experiences akin to the impact of GPS and motion-sensing accelerometers in current systems.

DARPA Program Manager Joshua Conway envisions a MOABB-enabled helicopter or drone flying low over a dense forest canopy, providing instantaneous range and velocity data for everything up to a football field’s distance with camera-like resolution. Accompanying visualization tools would create an experience as if one were on the ground with an unobstructed view.

Conway notes that every machine interacting with the 3D world, including manufacturing robots, UAVs, cars, or smartphones, could potentially be equipped with a chip- or wafer-scale LIDAR. The MOABB program, with an envisioned five-year timeline and up to $58 million in funding, could revolutionize LIDAR technology and its applications.

Breakthroughs in Foliage Penetration LiDAR

Several advancements are contributing to LiDAR’s improved performance in penetrating foliage:

• Multi-Wavelength Techniques: New LiDAR systems utilize multiple laser wavelengths. While leaves might reflect one wavelength strongly, another wavelength might pass through, revealing the hidden ground beneath.
• Polarization Detection: By analyzing the polarization of the reflected laser light, some LiDAR systems can differentiate between leaves and ground surfaces, offering a clearer picture.
• Advanced Signal Processing Techniques: Sophisticated algorithms are being developed to filter out noise caused by leaves and enhance the signal from the ground, leading to more accurate data.

Commercially Available Foliage penetrating LIDARs

LIDAR on manned and unmanned airborne platforms has unlocked a new realm of possibilities for detecting targets concealed beneath dense foliage. Whether used for environmental monitoring, disaster response, or archaeological exploration, LIDAR’s ability to penetrate vegetation offers valuable insights that were previously hidden from view. As technology continues to advance, the fusion of LIDAR with airborne platforms promises to shape a more efficient, sustainable, and secure future for various industries and applications.

 

References and Resources also include:

http://www.vision-systems.com/articles/print/volume-21/issue-9/departments/technology-trends/research-development-single-chip-lidar-sensor-developed-by-mit-and-darpa.html

http://www.design-engineering.com/foliage-penetrating-lidar-1004026949/

https://www.fbo.gov/index?s=opportunity&mode=form&tab=core&id=9c604bd41de0aa4fe7213412302aa6d2

http://www.militaryaerospace.com/articles/2017/01/lidar-tactical-mapping-uavs.html