Carl Weimer - Academia.edu (original) (raw)

Papers by Carl Weimer

Optical Sensors and Sensing Congress

2018 IEEE Aerospace Conference

Active hazard detection and avoidance will be required for landing on Europa due to a lack of a p... more Active hazard detection and avoidance will be required for landing on Europa due to a lack of a priori knowledge of surface features similar in size to the lander. A light detection and ranging (lidar) instrument can provide both long distance (8 km) ranging and close-range (500 m) imaging to enable real-time hazard detection during landing operations. An example space-qualified lidar instrument is the Vision Navigation Sensor (VNS) on the Sensor Test for Orion Relative-navigation Risk Mitigation (STORRM) mission in 2011 on STS-134. The VNS consists of a single box housing a laser, transmit and receive optics, focal plane assembly, electronic assemblies, and mechanical components. The instrument operates in dual mode to change the field of illumination for near or far targets. On STS-134 the VNS successfully acquired range and intensity images as the Shuttle docked with ISS. The VNS was subsequently installed on ISS in February, 2017, as part of NASA's Raven technology demonstration and is operating with more integrated processing algorithms. Raven's flash lidar observes vehicles as they approach and depart ISS, performing calculations onboard to test autonomous rendezvous capability. We present potential modifications to the VNS system that could address the unique challenges posed by the Europa environment and landing operations, while reducing payload size, weight and power. We present these different systems within the context of the landing Concept of Operations as laid out in the Europa Lander Science Definition Team Report.

Beam attenuation coefficient, c, provides an important optical index of plankton standing stocks,... more Beam attenuation coefficient, c, provides an important optical index of plankton standing stocks, such as phytoplankton biomass and total particulate carbon concentration. Unfortunately, c has proven difficult to quantify through remote sensing. Here, we introduce an innovative approach for estimating c using lidar depolarization measurements and diffuse attenuation coefficients from ocean color products or lidar measurements of Brillouin scattering. The new approach is based on a theoretical formula established from Monte Carlo simulations that links the depolarization ratio of sea water to the ratio of diffuse attenuation Kd and beam attenuation C (i.e., a multiple scattering factor). On July 17, 2014, the CALIPSO satellite was tilted 30deg off-nadir for one nighttime orbit in order to minimize ocean surface backscatter and demonstrate the lidar ocean subsurface measurement concept from space. Depolarization ratios of ocean subsurface backscatter are measured accurately. Beam atte...

ABSTRACT The Electronically Steerable Flash Lidar (ESFL) is a lidar concept created at Ball Aeros... more ABSTRACT The Electronically Steerable Flash Lidar (ESFL) is a lidar concept created at Ball Aerospace and developed in conjunction with NASA. It represents a new paradigm for airborne or spaceborne lidar remote sensing. Instead of the mechanical scanning common to airborne lidars, or the fixed beam approach found in spaceborne lidars, ESFL allows the number and position of transmitted beams to vary shot-to-shot. This is done using an acousto-optic beam deflector that splits a single laser beam into N output beams, where N and the position of beam N on the ground can be reconfigured in real time electronically. This transmitter concept is coupled with a Flash Focal Plane Array (FFPA), a pixilated detector where every pixel delivers a time-resolved intensity waveform, thus allowing lidar imaging. The ESFL enables several jumps in capability for remote sensing of ecosystems. Multiple spatial scales can be probed simultaneously or within the same flight transect because beam spacings can be varied in real time. This means contiguous beams can be applied to regions where smaller scale variability needs to be probed, and in areas where maximum across-track coverage is needed, those beams are spread out. Furthermore, each beam can be projected onto multiple pixels, allowing one to collect a waveform over multiple length scales simultaneously. The electronic interface with the AOBD means that the transmitted pattern can respond to any of a multitude of inputs. The ESFL can interface with another forward-looking sensor, such as a hyperspectral instrument or another lidar or a digital camera. The data from that second sensor could be used to direct the ESFL observation toward, for example, an area with a specific spectral signature, or an area free from clouds. The ESFL concept was designed with a path to space in mind, but an airborne version has been built and tested on aircraft. The work continues under a NASA Airborne Instrument Technology Transition (AITT) grant designed to improve the reliability of the instrument. The AITT work will culminate in the ESFL becoming a NASA facility instrument, so that time on ESFL can be proposed through NASA. This allows public access to ESFL and ideally a long-term stream of data to the ecological community. The overall flexibility of the transmitter pattern and ability to alter it to respond to a changing scene makes the ESFL well-suited for many applications such as forest science, but also to track rivers for hydrological studies. This poster will discuss recent analysis of ESFL data in forests to prove its applicability to estimate canopy height in airborne systems. Furthermore, we will discuss improvements to the ESFL that are underway as part of the AITT to improve data throughput, allow for higher altitude operation, and increase overall reliability of the instrument.

ABSTRACT Oceanographic lidars from space are a promising new technology for ocean observation. Th... more ABSTRACT Oceanographic lidars from space are a promising new technology for ocean observation. The success of the atmospheric lidar on the CALIPSO Pathfinder satellite has shown the feasibility of future space-based lidar instruments designed to measure ocean properties. Space-based laser, electronics, and detector technologies have advanced to a degree that allows the design of lidar systems with the power and speed to provide vertical profiling beneath the ocean surface while achieving the global coverage available from a space-based platform. An oceanographic lidar in space has the potential to provide an independent measure of sea surface wind speeds, relate ocean color surface properties to properties deeper in the column, assess diurnal variations of biological processes, investigate vertical profile of biomass, and quantify air-sea CO2 flux. This presentation discusses the potential capabilities of a modern, space-based oceanographic lidar. A radiometric model has been developed that relates instrument performance to expected ocean returns. Model results that show examples of retrieved sub-surface vertical profiles of such an instrument will be presented. We discuss how such profiles relate to ocean color parameters and to those measured in situ, as well as some of the expected science benefits provided by oceanographic lidars in space.

Ocean Sensing and Monitoring X

We are investigating the potential of the “vortex” laser beam to provide additional information o... more We are investigating the potential of the “vortex” laser beam to provide additional information of natural scenes from aircraft and space-based lidars. This type of beam has a spatial wavefront with a helical twist that creates an optical singularity on axis, and carries orbital angular momentum. We will report on preliminary results for differences in Rayleigh-Mie scattering, and scattering from rough surfaces, and plans for future studies.

Journal of Quantitative Spectroscopy and Radiative Transfer

Abstract Photon sieves (PS) have many applications and various designs in focusing light. However... more Abstract Photon sieves (PS) have many applications and various designs in focusing light. However, a traditional PS only has a light transmissivity up to ∼25% and a focusing efficiency up to ∼7%, which hinder the application of them in many fields, especially for satellite remote sensing. To overcome these inherent drawbacks of traditional PSs, a concept of reflective photon sieve is developed in this work. This reflective photon sieve is based on a transparent membrane backed by a mirror. The transparent membrane is optimally a fully transparent material sheet with given refractive index and designed geometric thickness which has an optical thickness of a quarter incident wavelength (i.e. an anti-reflective coating). The PS-patterned pinholes are made on the transparent membrane. The design makes the light reflected from pinholes and that from zones of membrane material have 180° phase difference. Thus, light incident on this optical device is reflected and focused on its focal point. This device can have a reflectivity of ∼100% and a focusing efficiency of ∼50% based on numerical simulation. This device functions similar to a concave focusing mirror but can preserve the phase feature of light (such as that for the light with orbital angular momentum). It also has excellent wavelength-dependent property, which can exclude most of the undesired light from the focal point. A thin sheet of this component can perform the joint function of lenses and gratings/etalons in the optical path of a remote sensing system, thus is suitable for controling/filtering light in compact instruments such as satellite sensors. This concept is validated by the finite-difference time domain (FDTD) modeling and a lab prototype in this study.

Optics express, Jan 24, 2017

Regular photon sieve (PS) may only have up to ~25% transmission of light. The low transmission li... more Regular photon sieve (PS) may only have up to ~25% transmission of light. The low transmission limits its applications in many fields such as satellite remote sensing when the reflected light incident on the PS is relatively weak. Binary PS was developed to overcome the low transmission problem of PS. However, binary PS which involves using different optical materials/thicknesses in different zones of the PS at a nanometer or micron scale, is not easy to manufacture. Therefore, in this study, we developed a fully transparent PS concept. We can use laser photolithography to simply make holes on a sheet of fully transparent material. With specifically designed optical thickness and PS-patterned pinholes, the transparent sheet can effectively focus light to its focal point. This concept is validated both by the finite-difference time domain (FDTD) modeling and by laboratory prototypes in this study.

2016 Progress in Electromagnetic Research Symposium (PIERS), 2016

Summary form only given. Electromagnetic (EM) beams with orbital angular momentum (OAM) may have ... more Summary form only given. Electromagnetic (EM) beams with orbital angular momentum (OAM) may have great potential applications in communication technology and in remote sensing of the Earth-atmosphere system and outer planets. Study of their interaction with optical lenses and dielectric or metallic objects, or scattering of them by particles in the Earth-atmosphere system, is a necessary step to explore the advantage of the OAM EM beams. In this study, the 3-dimensional (3D) scattered-field (SF) finite-difference time domain (FDTD) technique with the convolutional perfectly matched layer (CPML) absorbing boundary conditions (ABC) is applied to calculate the scattering of the purely azimuthal (the radial mode number is assumed to be zero) Laguerre-Gaussian (LG) beams with the OAM by dielectric particles. We found that for OAM beam's interaction with dielectric particles, the forward-scattering peak in the conventional phase function (P11) disappears, and light scattering peak occurs at a scattering angle of ~ 15-45°. The disappearance of forward-scattering peak means that, in laser communications most of the particle-scattered noise cannot enter the receiver, thus the received light is optimally the original OAM-encoded signal. This feature of the OAM beam also implies that in lidar remote sensing of the atmospheric particulates, most of the multiple-scattering energy will be off lidar sensors, and this may result in an accurate profiling of particle layers in the atmosphere or in the oceans by lidar, or even in the ground when a ground penetration radar (GPR) with the OAM is applied. This far-field characteristics of the scattered OAM light also imply that the optical theorem, which is derived from plane-parallel wave scattering case and relates the forward scattering amplitude to the total cross section of the scatterer, is invalid for the scattering of OAM beams by dielectric particles.

A subset of electrostatic modes of a cold cloud of electrons trapped in a Penning trap has been o... more A subset of electrostatic modes of a cold cloud of electrons trapped in a Penning trap has been observed and identified using a recent theoretical model. The detection of these modes is accomplished using electronic techniques which could apply to any ion species. The modes are observed in the low density, low rotation limit of the cloud where the electrons

Journal of Quantitative Spectroscopy and Radiative Transfer, 2016

Electromagnetic (EM) beams with orbital angular momentum (OAM) may have great potential applicati... more Electromagnetic (EM) beams with orbital angular momentum (OAM) may have great potential applications in communication technology and in remote sensing of the Earth- atmosphere system and outer planets. Study of their interaction with optical lenses and dielectric or metallic objects, or scattering of them by particles in the Earth-atmosphere system, is a necessary step to explore the advantage of the OAM EM beams. In this study, the 3-dimensional (3D) scattered-field (SF) finite-difference time domain (FDTD) technique with the convolutional perfectly matched layer (CPML) absorbing boundary conditions (ABC) is applied to calculate the scattering of the purely azimuthal (the radial mode number is assumed to be zero) Laguerre-Gaussian (LG) beams with the OAM by dielectric particles. We found that for OAM beam's interaction with dielectric particles, the forward-scattering peak in the conventional phase function (P11) disappears, and light scattering peak occurs at a scattering angle of ~ 15° to 45°. The disappearance of forward-scattering peak means that, in laser communications most of the particle-scattered noise cannot enter the receiver, thus the received light is optimally the original OAM-encoded signal. This feature of the OAM beam also implies that in lidar remote sensing of the atmospheric particulates, most of the multiple-scattering energy will be off lidar sensors, and this may result in an accurate profiling of particle layers in the atmosphere or in the oceans by lidar, or even in the ground when a ground penetration radar (GPR) with the OAM is applied. This far-field characteristics of the scattered OAM light also imply that the optical theorem, which is derived from plane-parallel wave scattering case and relates the forward scattering amplitude to the total cross section of the scatterer, is invalid for the scattering of OAM beams by dielectric particles.

ABSTRACT The lidar on the Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations (CAL... more ABSTRACT The lidar on the Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations (CALIPSO) mission provides accurate ocean surface backscatter intensity at 1064nm wavelength. The measurements can be used for estimating ocean surface wind speed at CALIPSO's 70 m lidar footprint. We are developing the high spatial resolution ocean surface wind speed data product for all the CALIPSO measurements, starting from June 2006 and ending at the end of CALIPSO mission (likely 2012). Wind Speed probability distributions will be studied based on the high spatial resolution data and compared with QuikScat. Scale and shape parameters of the Weibull wind distributions are derived from the wind speed product, and their global and regional statistics, together with the CALIPSO wind speed product, will be made available to the research community. (Abstract) Keywords-component; formatting; style; styling; insert (key words) 1. CALIPSO lidar measurements The Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations (CALIPSO) mission is a satellite mission being developed within the framework of collaboration between NASA and the French space agency, CNES. The CALIPSO mission provides unique measurements to improve our understanding of the role of aerosols and clouds in the Earth's climate system. One of the CALIPSO mission's payload is a two-wavelength polarization-sensitive lidar. A diode-pumped Nd:YAG laser produces linearly-polarized pulses of light at 1064 nm and 532 nm. The atmospheric return is collected by a 1-meter telescope which feeds a three channel receiver measuring the backscattered intensity at 1064 nm and the two orthogonal polarization components at 532 nm (parallel and perpendicular to the polarization plane of the transmitted beam). Each laser produces 110 mJ of energy at each of the two wavelengths at a pulse repetition rate of 20.2 Hz. Only one laser is operated at a time. Beam expanders reduce the angular divergence of the laser beam to produce a beam diameter of 70 meters at the Earth's surface. The fundamental sampling resolution of the lidar is 30 meters vertical and 333 meters horizontal, determined by the receiver electrical bandwidth and the laser pulse repetition rate. Backscatter data are acquired from 0.5 km below the surface to 8 km above with 30 m vertical resolution. Backscatter data at coarser resolution are collected below and above that vertical altitude range (Figure 1).

IEEE International Frequency Control Symposium, 1995

As they apply to frequency standards and precision spectroscopy the characteristics and technolog... more As they apply to frequency standards and precision spectroscopy the characteristics and technology of tunable diode lasers are briefly reviewed. It is now possible to use nonlinear optical techniques and high quality diode lasers to extend the useful wavelength coverage of semiconductor lasers into the UV, the IR and even millimeter-wave spectral regions. Progress in developing an all diode-laser system

Sea surface wind speed estimation from space-based lidar measurements Sea surface wind speed esti... more Sea surface wind speed estimation from space-based lidar measurements Sea surface wind speed estimation from space-based lidar

Optics express, Jan 13, 2016

Sunlight contamination dominates the backscatter noise in space-based lidar measurements during d... more Sunlight contamination dominates the backscatter noise in space-based lidar measurements during daytime. The background scattered sunlight is highly variable and dependent upon the surface and atmospheric albedo. The scattered sunlight contribution to noise increases over land and snow surfaces where surface albedos are high and thus overwhelm lidar backscatter from optically thin atmospheric constituents like aerosols and thin clouds. In this work, we developed a novel lidar remote sensing concept that potentially can eliminate sunlight induced noise. The new lidar concept requires: (1) a transmitted laser light that carries orbital angular momentum (OAM); and (2) a photon sieve (PS) diffractive filter that separates scattered sunlight from laser light backscattered from the atmosphere, ocean and solid surfaces. The method is based on numerical modeling of the focusing of Laguerre-Gaussian (LG) laser beam and plane-wave light by a PS. The model results show that after passing throu...

Thesis (Ph. D.)--Colorado State University, 1992. Includes bibliographical references (leaves [16... more Thesis (Ph. D.)--Colorado State University, 1992. Includes bibliographical references (leaves [165]-171).

Physical Review Letters, 1993

... Mod. Phys. 58, 233 (1986) [SPIN];[INSPEC];[CAS];[SPIRES]. Earl C. Beaty, J. Appl. Phys. 61, 2... more ... Mod. Phys. 58, 233 (1986) [SPIN];[INSPEC];[CAS];[SPIRES]. Earl C. Beaty, J. Appl. Phys. 61, 2118 (1987), and unpublished calculations. ... Rev. Lett. 67, 3090 (1991) [SPIN];[INSPEC];[CAS];[MEDLINE].Carl S. Weimer, Ph.D. thesis, Colorado State University, 1992. ...