1,307 research outputs found
ALART: A novel lidar system for vegetation height retrieval from space
We propose a multi-kHz Single-Photon Counting (SPC) space LIDAR, exploiting low energy pulses with high repetition
frequency (PRF). The high PRF allows one to overcome the low signal limitations, as many return shots can be collected
from nearly the same scattering area. The ALART space instrument exhibits a multi-beam design, providing height
retrieval over a wide area and terrain slope measurements. This novel technique, working with low SNRs, allows
multiple beam generation with a single laser, limiting mass and power consumption. As the receiver has a certain
probability to detect multiple photons from different levels of canopy, a histogram is constructed and used to retrieve the
properties of the target tree, by means of a modal decomposition of the reconstructed waveform. A field demonstrator of
the ALART space instrument is currently being developed by a European consortium led by cosine | measurement
systems and funded by ESA under the TRP program. The demonstrator requirements have been derived to be
representative of the target instrument and it will be tested in an equipped tower in woodland areas in the Netherlands.
The employed detectors are state-of-the-art CMOS Single-Photon Avalanche Diode (SPAD) matrices with 1024 pixels.
Each pixel is independently equipped with an integrated Time-to-Digital Converter (TDC), achieving a timing accuracy
that is much lower than the SPAD dead time, resulting in a distance resolution in the centimeter range. The instrument
emits nanosecond laser pulses with energy on the order of several J, at a PRF of ~ 10 kHz, and projects on ground a
three-beams pattern. An extensive field measurement campaign will validate the employed technologies and algorithms
for vegetation height retrieval
Continuous-variable optical quantum state tomography
This review covers latest developments in continuous-variable quantum-state
tomography of optical fields and photons, placing a special accent on its
practical aspects and applications in quantum information technology. Optical
homodyne tomography is reviewed as a method of reconstructing the state of
light in a given optical mode. A range of relevant practical topics are
discussed, such as state-reconstruction algorithms (with emphasis on the
maximum-likelihood technique), the technology of time-domain homodyne
detection, mode matching issues, and engineering of complex quantum states of
light. The paper also surveys quantum-state tomography for the transverse
spatial state (spatial mode) of the field in the special case of fields
containing precisely one photon.Comment: Finally, a revision! Comments to lvov(at)ucalgary.ca and
raymer(at)uoregon.edu are welcom
Improving Range Estimation of a 3D FLASH LADAR via Blind Deconvolution
The purpose of this research effort is to improve and characterize range estimation in a three-dimensional FLASH LAser Detection And Ranging (3D FLASH LADAR) by investigating spatial dimension blurring effects. The myriad of emerging applications for 3D FLASH LADAR both as primary and supplemental sensor necessitate superior performance including accurate range estimates. Along with range information, this sensor also provides an imaging or laser vision capability. Consequently, accurate range estimates would also greatly aid in image quality of a target or remote scene under interrogation. Unlike previous efforts, this research accounts for pixel coupling by defining the range image mathematical model as a convolution between the system spatial impulse response and the object (target or remote scene) at a particular range slice. Using this model, improved range estimation is possible by object restoration from the data observations. Object estimation is principally performed by deriving a blind deconvolution Generalized Expectation Maximization (GEM) algorithm with the range determined from the estimated object by a normalized correlation method. Theoretical derivations and simulation results are verified with experimental data of a bar target taken from a 3D FLASH LADAR system in a laboratory environment. Additionally, among other factors, range separation estimation variance is a function of two LADAR design parameters (range sampling interval and transmitted pulse-width), which can be optimized using the expected range resolution between two point sources. Using both CRB theory and an unbiased estimator, an investigation is accomplished that finds the optimal pulse-width for several range sampling scenarios using a range resolution metric
Measuring Shadows: FPGA-based image sensor control systems for next-generation NASA missions
Astronomy and astrophysics are fields of constant growth and exploration, and discoveries are being made every day. Behind each discovery, however, is the equipment and engineering that makes that science possible. The science and engineering go hand in hand in two ways: advances in engineering make new scientific discoveries possible, and new scientific questions create the need for more advanced engineering. The work that led to this thesis is an example of the latter statement. The big-picture goal is to support the development of next-generation detectors such as the Quanta Image Sensor (QIS), a gigapixel-scaleble Complementary Metal-Oxide Semiconductor (CMOS) photon-number resolving image sensor. This thesis focuses on one crucial part of the development process: the characterisation of the QIS. In order to advance the NASA Technology Readiness Level (TRL) from three to four, the detector needs to undergo extensive laboratory and telescope environment testing. The testing framework is being run by an FPGA hardware design that includes a processor, and this set of hardware and software is responsible for operating the detector, managing experiment parameters, running experiments, and collecting resultant data and passing it to a host PC. The majority of the work of this portion of the project revolved around creating, improving, and testing the framework to allow for fully functional and automated detector characterisation. Test systems already exist for the QIS in a room temperature environment, as well as for current-generation image sensors in cryogenic vacuum environments. However, there is no existing test system that allows the QIS to be tested in a cryo-vac environment. This thesis details a functional system that fills that niche. The system is built to be modular and extensible so that it can be expanded upon to characterise other types of detectors in the future as well. For now, however, the system shines as the only one that allows the QIS to be tested in an environment that simulates its behaviour in outer space
Remote sensor systems for unmanned planetary missions
Development, definition, and characteristics of remote sensors for unmanned spacecraft conducting planetary exploratio
The Airborne Cloud-Aerosol Transport System
The Airborne Cloud-Aerosol Transport System (ACATS) is a multi-channel Doppler lidar system recently developed at NASA Goddard Space Flight Center (GSFC). A unique aspect of the multi-channel Doppler lidar concept such as ACATS is that it is also, by its very nature, a high spectral resolution lidar (HSRL). Both the particulate and molecular scattered signal can be directly and unambiguously measured, allowing for direct retrievals of particulate extinction. ACATS is therefore capable of simultaneously resolving the backscatterextinction properties and motion of a particle from a high altitude aircraft. ACATS has flown on the NASA ER-2 during test flights over California in June 2012 and science flights during the Wallops Airborne Vegetation Experiment (WAVE) in September 2012. This paper provides an overview of the ACATS method and instrument design, describes the ACATS retrieval algorithms for cloud and aerosol properties, and demonstrates the data products that will be derived from the ACATS data using initial results from the WAVE project. The HSRL retrieval algorithms developed for ACATS have direct application to future spaceborne missions such as the Cloud-Aerosol Transport System (CATS) to be installed on the International Space Station (ISS). Furthermore, the direct extinction and particle wind velocity retrieved from the ACATS data can be used for science applications such 27 as dust or smoke transport and convective outflow in anvil cirrus clouds
Data security in photonic information systems using quantum based approaches
The last two decades has seen a revolution in how information is stored and transmitted
across the world. In this digital age, it is vital for banking systems, governments and
businesses that this information can be transmitted to authorised receivers quickly and
efficiently. Current classical cryptosystems rely on the computational difficulty of
calculating certain mathematical functions but with the advent of quantum computers,
implementing efficient quantum algorithms, these systems could be rendered insecure
overnight. Quantum mechanics thankfully also provides the solution, in which
information is transmitted on single-photons called qubits and any attempt by an
adversary to gain information on these qubits is limited by the laws of quantum
mechanics.
This thesis looks at three distinct different quantum information experiments. Two of
the systems describe the implementation of distributing quantum keys, in which the
presence of an eavesdropper introduces unavoidable errors by the laws of quantum
mechanics. The first scheme used a quantum dot in a micropillar cavity as a singlephoton
source. A polarisation encoding scheme was used for implementing the BB84,
quantum cryptographic protocol, which operated at a wavelength of 905 nm and a clock
frequency of 40 MHz. A second system implemented phase encoding using asymmetric
unbalanced Mach-Zehnder interferometers, with a weak coherent source, operating at a
wavelength of 850 nm and pulsed at a clock rate of 1 GHz. The system used
depolarised light propagating in the fibre quantum channel. This helps to eliminate the
random evolution of the state of polarisation of photons, as a result of stress induced
changes in the intrinsic birefringence of the fibre. The system operated completely
autonomously, using custom software to compensate for path length fluctuations in the
arms of the interferometer and used a variety of different single-photon detector
technologies. The final quantum information scheme looked at quantum digital
signatures, which allows a sender, Alice, to distribute quantum signatures to two parties,
Bob and Charlie, such that they are able to authenticate that the message originated
from Alice and that the message was not altered in transmission
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