This PDF file contains the front matter associated with SPIE Proceedings Volume 13472, including the Title Page, Copyright information, Table of Contents, and Conference Committee information.

Multiwavelength lidars can be used to spectrally map the surface of planetary bodies to find and quantify volatiles regardless of natural illumination conditions. Using a set of selected laser wavelengths to illuminate the surface, lidars can peer into shadowed regions and observe nighttime surfaces. NASA Goddard Space Flight Center (GSFC) is developing the Spectroscopic Infra-Red Reflectance Lidar (SpIRRL) for lunar surface volatile measurements. SpIRRL uses three Intra-cavity Optical Parametric Oscillator (IOPO) lasers pumped by Nd:YAG lasers at 1.064 μm. The IOPO crystal converts a 1.064- μm photon into a pair of photons with the same combined photon energy but at two longer wavelengths. The IOPO laser wavelengths were chosen to be 2.670, 2.900, and 3.100 μm in the mid-wave infrared (MWIR) to map water ice and hydroxyl on the Moon at the strongest available absorption lines. The corresponding three laser outputs in the short-wave infrared (SWIR) are used to measure more abundant water ice absorption in the 1.6-1.8 μm band and constrain the lunar spectral continuum. The lidar receiver uses two HgCdTe avalanche photodiode arrays, one for the MWIR channel and one for the SWIR channel. SpIRRL measures the transmitted and received laser pulse energies and time-of-flight to derive the surface reflectance. SpIRRL also measures background radiance in between the short laser pulses, which is used to remove the effects of solar illumination and surface thermal emission in the laser reflectance measurements. In this presentation, we will describe the instrument design and performance analysis as well as the recent progresses in our prototype instrument development.

Adding polarimetric capabilities to a remote sensing system provides more information about the scene than would be available from a system without polarization sensitivity. One example is scene characterization with Mueller matrices, which can be measured by an active polarimeter, consisting of a polarization state generator and a polarization state analyzer. Incoherent lidars have been built around this concept, often using a bistatic configuration with a polarization state generator in the transmitted beam path and an independent polarization state analyzer in the received beam path. Coherent lidars have yet to make significant use of polarimetric information owing to the more complicated lidar architecture. Here we present a simple monostatic coherent (frequency-modulated continuous-wave) lidar with potential capability of measuring ten of the sixteen Mueller matrix coefficients. This is made possible through the use of two liquid crystal variable retarders acting as both the polarization state generator and polarization state analyzer. This paper describes the design and calibration of this instrument with preliminary measurements.

Range-resolved backscattered energy from an aerosol cloud at a single wavelength can be inverted to retrieve the aerosol extinction and its backscattering-to-extinction ratio. A single measurement does not bring much information about the aerosol effective size or its nature, but a measurement made at two wavelengths, like the ˚Angstr¨om exponent method, can provide information on the size or the type of the probed aerosol. Adding wavelengths helps refine our knowledge of the aerosol. Advances in tunable pulsed sources technology and in supercontinuum pulsed lasers open the way to multispectral lidars able to probe a continuum of wavelengths ranging from the visible to the infrared. In this paper, we present measurements performed using a tunable source at 28 wavelengths ranging from 420 nm to 1800 nm through a fogoil and a graphite aerosol. A 532 nm lidar is used as a reference to provide a stand-off extinction measurement at all times. This reference measurement is used to convert the measured spectral extinction to relative spectral extinction efficiency. We show how the spectral extinction efficiency can provide valuable information not only on the effective size of the aerosol particles, but also on the size distribution. Once the aerosol extinction is known, we can retrieve its spectral backscattering-to-extinction ratio. Used with the effective size previously found, the spectral backscattering-to-extinction ratio can serve as a signature marker to help establish the nature of the observed aerosol.

In this manuscript we cover our developments using dual-polarization lidar for bathymetric retrievals. We are investigating the use of this lidar technique to identify surface and bottom returns in shallow water applications. In shallow water the returns for the surface and bottom can overlap and create difficulty when attempting to measure the depth. With our dualchannel approach, we can take advantage of the depolarizing nature of the bottom return. This allows for the surface return to appear strongly in the co-polarized channel while the bottom return appears strongly in the cross-polarized channel. We are testing the use of the wavelet transform on the ratio of cross-polarized signal to co-polarized signal. The wavelet transform can help to identify the surface and bottom returns when the data are noisy. Occasionally, the surface echo will appear in the cross-polarized channel with the bottom echo. Using the depolarization ratio for identifying the bottom echo is advantageous in this case over using the co-polarized or cross-polarized data alone. We will present our current findings as well as discuss potential future approaches to the analysis of the data.

This paper presents the development of Scheimpflug cameras for lidar and remote sensing with an emphasis on active and passive range-finding. Scheimpflug technology uses a tilted camera geometry to natively encode 3D information through projected off-axis pixel view angles and holds the unique potential to serve as an alternative to traditional lidar and remote sensing systems with the demonstrated advantages of high configurability, SWaP-C (Size, Weight and Power-Cost) efficiency, and short- vs. far-range optimization. In this work, we demonstrate a compact Scheimpflug-enabled system as a snapshot atmospheric lidar detector to measure aerosol extinction and optical turbulence effects with high precision over ranges from a few meters to a few kilometers. We compare the instrument’s measurements to variance-based Cn2 data collected by a sonic anemometer and a scintillometer over a 50 m horizontal path. This paper also presents preliminary results on utilizing Scheimpflug technology for photogrammetry, 2D/3D mapping and includes a generalized discussion on design, alignment, and calibration procedures. We believe this work provides a strong basis for the broad use of Scheimpflug technology across multiple use-cases within the fields of lidar and remote sensing.

We have designed and developed a breadboard of a small atmospheric lidar to measure the vertical profiles of dust, water vapor and winds in the lower Mars atmosphere from its surface. Our approach remotely profiles aerosols, atmospheric water vapor and winds by using a laser that emits near 1911 nm and using a direct detection receiver. The lidar measures vertically resolved profiles of water vapor by using a tunable single-frequency Tm-fiber laser pulsed at a 10 kHz pulse rate. The laser is tuned onto and off the strong isolated water vapor absorption lines and water vapor profiles will be determined via the differential absorption lidar (DIAL) technique. The same laser is used for measuring the aerosol and wind profiles by tuning the laser off-line and by resolving the Doppler shift in the aerosol backscatter profiles. The lidar receiver uses a 12-cm lens-type telescope and a 16-pixel HgCdTe avalanche photodiode (APD) as the detector.

Coherent lidar is seeing a resurgence of interest due to the advent of solid-state narrow-linewidth sources and integrated amplifiers and modulators. At the Geophysical Institute’s Lidar Research Lab (LRL) we are developing a 532 nm frequency-modulated continuous wave (FMCW) breadboard lidar to investigate the capabilities of coherent lidar in the underwater environment. Coherent systems have some advantages over traditional incoherent lidar, including optimal detection, background insensitivity, and the exciting possibility of remotely profiling water current. Coherent lidar can easily achieve millimeter-level range resolution without the need for exotic ultrashort pulse lasers and high-performance timing. Here, we present the modeling, design, and expected performance of the system against submerged diffuse and specular hard targets using established statistical methods (e.g. Goodman, Osche) and oceanographic lidar theory (e.g. Churnside). Current status of the breadboard lidar development will also be reviewed.

Alaska has more coastline than the entire contiguous United States and many Alaskan coastal communities are uniquely vulnerable to the continuing effects of global environmental change. Accurate and timely bathymetric data are critical for these communities to plan for and address increasing shoreline erosion and flooding. Most of these communities are not accessible by road, creating a major challenge for data collection and a unique opportunity for droneborne bathymetric lidar instruments to have a significant impact.

At the Geophysical Institute’s Lidar Research Lab (LRL) we are developing an incoherent, polarimetric 532 nm scanning bathymetric lidar system to operate on a fixed-wing vertical take-off and land (VTOL) drone platform. This VTOL drone has a 25 m/s cruise speed and a flight endurance of 900 km. The lidar design leverages state-of-the-art technology to reduce the cost, size, weight, and power (C-SWaP) of the traditional airborne lidars for flight on the drone platform. The current status of the design will be reported, as well as modeling results showing the signal-to-noise ratio and expected depth performance. We also determine the optimal spot diameter for bathymetric profiling in Alaskan waters where this system will be fielded.

Processing of bathymetric lidar waveforms is a complex task as the target situation is more complex when measuring into the water than on solid ground. Furthermore, the echo signal from the water bottom is getting very weak usually only after a couple of meters water depth due to absorption and scattering. Best results are achieved when addressing the entire waveform as a whole rather than decompose it into individual parts. Pre-detection averaging can be employed to increase the signal to noise ration (SNR) and thereby the penetration depth. We present methods for performing fast and efficient waveform averaging and for training a deep-learning network to provide initial values for the waveform analysis based on exponential decomposition.

Historically, Digital Terrain Models (DTMs) of foliated areas have suffered from low accuracy and low spatial resolution, due to limited data density under foliage. The foliage penetration (FOPEN) capabilities afforded by Geiger-mode(GM) lidar enable high-density, fine-resolution data products, even under heavy canopy. In this paper we evaluate the application of existing ground finding algorithms to Geiger-mode data sets.  We discuss the requirements for data collection, including angular diversity and data density, and how data collection parameters impact accuracy and resolution of DTMs. We present the results of the ground estimation and evaluate the robustness of the results across data variations.

Two defense related applications are investigated: (1) long-range 3D imaging and range finding for ISR missions and (2) 3D imaging for precision missile seeker guidance. High performance detectors or high powered lasers aid in long range capabilities, but can be cost-prohibitive. Automotive-grade LiDAR, autolidar, systems are produced in high volume, and typically use lower cost components, such as silicon detectors, enabling affordable solutions in a commercial market. In the explored defense applications, both scenarios assume the platforms are expendable, therefore affordability is priority just as in the commercial market. However, the commercial autolidars do not directly translate to use in critical missions due to their shorter range and lower resolution. In an effort to enable a low-cost, attritable LiDAR platform that can be exercised in large volumes, Exciting Technology has adapted two of its beam steering technologies for a scanning 3D imager. A small format GMAPD array is paired with a fiber laser and is rapidly scanned across an area of interest. A hybrid design of both wide-angle mechanical steering and rapid, narrow angle non-mechanical scanning is developed. The LiDAR steering system can be packaged more compact than traditional gimbals, more stable than fast-steering mirrors or galvanometers, and with better optical quality and performance than Risley prisms. We take a macro-pixel approach to image processing to extend to further ranges. High resolution 3D imaging is not a new concept, but the ability to combine these typically cost-prohibitive components into a package affordable for thousands of attritable platforms is a strategy-shifting innovation for defense.

Multiple positive feedback loops are formed within a microwave photonic CMOS transistor, where an ultra low resistance threshold-less laser and tunnel microwave diode are in the CMOS drain region, and photon sensors and avalanche photo diodes are in the CMOS drain and well regions. Interdigitated Lasers, microwave diodes, photon sensors and CMOS are fabricated as one integral transistor. The device is capable of producing high power laser beams and photon modulated millimeter wave signals for telecommunications. Comparing with traditional discrete diode lasers, high power CMOS lasers are more thermally stable, with better quantum efficiency. Comparing with conventional discrete microwave diodes, high efficiency millimeter wave photon CMOS offers superior light wave and microwave nonlinear optical operations for signal modulation and polarization. In this article we would like to demonstrate microwave photonic CMOS as a reliable source for next generation advanced radar and lidar technologies, with superior microwave and light wave sensing capabilities.

The implementation of bistatic Camera LiDAR (CLiDAR) systems for atmospheric studies represents a significant advancement in accessible remote sensing technology. CLiDAR is a relatively novel technology that has thus far primarily employed a single detector for data collection and atmospheric analysis. In this study, we compare data from two simultaneous-capture detectors at varying distances from the laser to gain insight on aerosol scattering properties. Comparisons of results from two detectors demonstrate the potential of this technology for atmospheric analyses in the field.

FMCW lidar is an emerging sensor technology that is purported to be nearly immune to interference, unlike the more common pulsed lidars. However, while FMCW lidars may be more resistant, we outline the conditions under which interference may result and demonstrate interference in simulation. This work presents a MATLAB-based simulator to investigate the effects of mutual interference on FMCW lidars. We introduce the conditions that should be satisfied for mutual interference to occur: spatial, spectral, and temporal alignment. We then focus on direct interference, where a lidar is receiving the transmission from another lidar directly. We show simulated results for a lidar experiencing interference which can cause, among others, false or ghost targets and a degradation in detector performance.

Using a LiDAR point cloud and optical image, it is possible to create a fused LiDAR image (known as a texel image). Texel images only have the ability to reconstruct topographical and visual features of a single scan; it is possible to combine multiple texel Images into a larger 3D terrain map called a Textured Digital Surface Model (TDSM). TDSMs provide valuable information in fields such as natural disaster response, agriculture, and infrastructure development. In spite of their utility, current techniques often misrepresent concave objects such as caves, overhangs, doorways, or outcroppings during the texturing process. This flaw can significantly change the final 3D terrain map and limit its effectiveness in certain scenes.

This paper describes a method of texturing TDSMs that improves the tessellation of concave object by modifying the Ball-Pivoting Algorithm (BPA). The new approach addresses the loss of information caused in 3D point projection by more effectively mapping registered point clouds to 3D surfaces while preserving surface curvature. To evaluate the effectiveness of the new texturing technique, several examples are presented that use real-world data acquired using a LiDAR sensor, optical camera, and inertial navigation system. These data are acquired such that measurements from all three are combined to form a calibrated texel image and subsequently registered together to form a TDSM. After applying both the new and the previous texturing techniques, the fidelity of the final 3D scenes are compared. Through these comparisons, we demonstrate improvements in texturing, especially concerning concave objects.

Accurate weather observations and forecasts are becoming increasingly important in the space launch community and for the nation's defense. We are constantly affected by the conditions around us, impacting short- and long-term planning, daily operations, military activities, and maintaining safety and security for the general public. Utilizing soft-target LiDAR, an optical sensing technique capable of providing fast and accurate measurement of many atmospheric properties, Honeywell’s High-Altitude LiDAR Atmospheric Sensing (HALAS) technology is being used to improve data quality in many markets including defense, space launch, and commercial weather. Spatially and temporally relevant measurements of range-resolved wind, humidity, temperature, density, and other parameters into and beyond the stratosphere are enabling improved weather forecasting and rapid go/no-go decision making in several aerospace and defense markets. This presentation will summarize the HALAS technology and several markets where it is being employed. Example weather observations will be shared along with their utility.

Publisher's Note: this paper, originally published on 29 May 2025, was replaced with a corrected/revised version on 27 August 2025. If you downloaded the original PDF but are unable to access the revision, please contact SPIE Digital Library Customer Service for assistance.